Repair Briefs - Guitar Amplifiers, Band/Stage Gear, L to O
The following are repair briefs for various
equipment.The infomation is directed
to technically competant repair engineers.Generic terms have
been used to make this info less model specific,eg terms like
replace transistor Q123 have not been used.
The equipment is Guitar Amplifiers, Audio Amplifers, Stage Gear.
I would be interested in finding
any other repair listings on the internet structured as i have
done ie intended to be less model specific. For convenience using search-engines,
use keyword divdevrep to target these files.
There is no point in contacting me about any of the following, the
repair job may have been done 15 years ago .
I cannot clarify or enlarge on any of the following.
In the following V ac means RMS DVM AC volts
unless stated pk-pk. Mains is 240V, UK
Should the location of this file change please use the keyword "divdev7" in
a search engine to find it again
A number of the pictures are now apparently not downloadable, because the hosts have disallowed
remote linking although not saying so. To view them , you have to remove the picture file name
from the picture URL and put this .htm file name in its place
and scroll down to the relevant pic.
Band Amps and other stage gear , L to O
Lab Gruppen amps, Lab Gruppen, pro series of amps
Check whether 2 ch amps are run with antiphase outputs , ie swapped ground and live terminals, inverter/
inversion within one channel somewhere.
AB Landola semi-acoustic guitar electrics ,c 1960s
I worked out how to remove the electrics through the frettedwork, all sorts of
minor problems in the wiring etc but main one is no signal from one of the
pickups.
One pickup measures 7.7K and the other megohms
There is some useful dating info on
http://www.landola.fi/dating_your_guitar.html
but to get it tighter the pots are 4 off 250K marked Prem (looks like) and
a 4, along with the 250K stamped into the monkey metal is the number 437.
Unfortunately 4 off the same pots so don't know if a type number or week 37
of 1964 . This one has serial number in the 109 thousands.
caps are marked ERD FOL and 2 vertical lines like mark 2
I trod carefully and ground through the solder on the rear of the pickup
with a Dremmel. Just as well as the magnets are directly over the brass.
Chromed cover plate removed.
The output screened lead goes into the tissue paper, lower left
http://home.graffiti.net/diverse:graffiti.net/landola_pu1.jpg
looks as though no varnish /laquer and and just wrapped in tissue paper but
light hooking under does not shift the coil. Would it be glued underneath ,
unseen? Surely it would not be loosely laid in there with just compressed
tissue paper holding it in place. Turned out it was lacquered in and
so defeated counting off turns. Very thin bakelite (the pinkish colour
trough) so must be incredibly fragile 45 years on.
The paper and coil was lightly laquered in, not as obvious as magneto coil.
With child's toy wooden clothes peg, one wedge of, and small plectrum managed
to ease out the coil with only minor collateral damage to the wire and no
damage to the bakelite (will have to chemically clean oput the glued in
paper). Taken dimensions and weight to 10mg so should be able to rewind
another.
Looks like bad assembly, in that in the process of wrapping the tissue paper
strip around the coil , the lay had been seriously disturbed and then
probably vibration/thermal changes/chaffing enough to make a break
somewhere. From the owner the odd woodscrew is for a now missing
finger/scratch plate.
This is a 12 string version
http://www.hagstrom.org.uk/Other/Landola12/P1000606.jpg
of the same guitar, the one I have here is a 6 string, deep cherry colour
version and tremolo arm.
After 1961, before 1973, the serial number 109,000s could put it in 1964 ,
according to "437" on the pots and roughly mid 60s via the hagstrom dating
file.
Any idea of the pickup make? owner thinks Ibanez. No name/numbers found on /in them, Landola own
?, the ones here look identical to the ones on that 12 string version,
offset slots, chrome cover, black bakelite base, screw positions etc.
Exactly the same fretwork , so quite a chinese puzzle removing the 2 off
paired up pots and brasswork out through the slot. The same "crackalure"
evident on the top face of the body in that pic
pic I took , before tying back the internal wiring
http://home.graffiti.net/diverse:graffiti.net/landola2.jpg
http://home.graffiti.net/diverse:graffiti.net/landola3.jpg
With some Pekalit red bakelite and brass knobs I have a supply of
, far more in keeping than
the "original" ? aluminium Japanese ones.
Trough for the winding hank is 56.5x3mm to 70x14 x 6.4mm deep.
The rewinding former has to be demountable.
A plastic booklet binder spine warmed up and opened out to a flat
bottomed slight V and then gripped with small square rod and
heated again to form a steeper V section. Round all exposed
edges. Doubled up 60mm long, end over end, and 2 cuts per side deep into the V sections , so can easily
cut the remainder after winding. A small piece of metal tube
pushed through the binder spine to mount in the coil winder.
Otherwise fine wire coilwinding dealt with on my tips pages.
Some thick PTFE wound around to decrease
the width a bit to match the trough dimension, some thin elastic laid across , so under
the wiring, to tie together in loops after winding. Then some thin PTFE
over the sides so nothing to catch the wire. To join 0.05mm wire
to intermediary 0.5mm wire (will work for 0.05/0.05 mm join), strip varnish with lightest of
touch with Dremmel grinding disc. Grab the ends with a toy wooden clothes
peg and twist. Coat with solder paste to solder, and a small dab
of hotmelt string for more mechanical strength.
Another not so obvious tip for winding such fine wire,
cut your fingernails and sand paper , so nothing to catch , and good lighting.
More "ghost cocoon" elastic spiralled through/round the hank
before setting in the trough.
Lacquer in place , including the elastic.
125W soldering iron to remake 6 solder
points of the brasswork, such indirect heating of the wiring made
the coil resistance increase 500R. Beware of the signal screened
cable comeing out between brass sections, not through the hole underneath or
the pickup position will not be adjustable due to fouling under.
The original one probably failed because in the process of wrapping with
tissue paper and adjusting to fit into the trough , the layup was seriously
disturbed/ stressed, before lacquering.
Removing the brasswork ,holding the pots.
Undo the 3.5mm sockets , but leave pots in place.
Turn so pot shafts poke through the large hole and end circle,
then angle so one pot comes through the large
central hole, then angle down the slot to remove the second one
1, 250K
2 250K
3, 470R 250K pot
4 47K, 250K pot
2 C 0.022/10/400 150V, 50Hz
If re-using the original steel woodscrews, grind off the rust
as turning to undo broke the flimsy small
edge of the black bakelite pickup surround, used hotmelt
string with copier toner included to "repair"
Using a 390uH wireended axial choke for injector
in place of guitar string and an AF generator
and comparing roughly the frequency response.
The rewind was about the same at 100Hz , less
at 1KHz and more at 8 KHz
Laney AH100, 2006
Victim of RoHS / PbF, excellent customer symptom observation
"The amp would often hum, and when the volume is half way up, any
keyboard played through it would crackle very loudly. Also if you rock
the amp gently the crackle would appear, also if you jump it would
make a crackling sound. "
2 year old amplifier built into a
vibrating box (combo amp and speaker). It has 2 failed solder joints and
about 10 visibly and tug-test near to failure joints and perhaps 20 that
will fail in the next 5 years perhaps. Where is there a non technical
article on the WWW that explains the problems of unforgiving hard brittle
solder/ tin pest, for customers . I can find plenty of stuff on tin whiskers which really
only applies to fine geometry components , computers mainly.
PA LN2 chassis grounding screw dropped out , despite lacquer, and the other one poor contact
due to paired wires compressing into the pcb. Tightened all and added star washers on the
underside screws as well as lacquer on all. To remove the front knobs
wooden wedge from a clothes peg.
Mains tr 24R//1.2R
Plenty of PbF and RoHS statements
4.6mm diameter and 4.3mm high lump of PbF solder on a wire joint , I've never seen the like.
1/4 inch spade connector blades loose enough to loose contact at high current/temp.
Redid all PA solder joints and all major PreA joints
General observation on this range of amps , for stable storage/ transport , because of that
rear projection , lay on a side.
Laney CD630M, 2008
Cracks and bangs
One of the orange wires easily pulled out of the "crimp" to the +60V line.
Removing totaly means relay drop out so presumably intermittant contact.
To gain access remove 4 screws on the top and 2 under
Laney CD630M
bad crackling reported but no problem found on receipt
top handle split , see tips to recover
bad spade cons on mains sw
checked underside of pa and redid usual suspect solderings
Laney CD850S
1ch failed to shorts and blowing mains fuse
1 emitter resistor failed leading to unbalanced loading at high throughput , then those remaining 2 failed to short
and taking out one of the 3 of its complement
Replaced the 2SC5200 and 2SA1943 with NJW21194G and NJW2193G
Bend pins to match removed ones before soldering in place
Laney CD850S, 2002
2x 200W mixer amp
Problem in protection (falsely triggering occassionally), both amps dropping
out.
Of course I have not been able to induce activation.
Remove 4 feet screws and 3 screws from each side to
remove the full metal case interior.
2 separate power amps otherwise apparently the same , both carying output DC
protect and overheat protect output relay drive ccts. But only one normally
open thermal switch going to one amp only so only dropping out that
relay and amp only with no interconnect to the other amp.
More likely a problem with the thermal sw or 12V supply to both protection
cct and the fan , rather than a fan problem as it did occur once at sound
check and once at switch on. The fan does stop when this happens so unlikely
a send/return bypass sw problem, the monitor outputs still continue to work
so not a mains failure problem.
There is also a thin low current , signal level earth wire from the ps that
had come adrift loose in the case , broken at some pcb solder point
presumably, somewhere indeterminate from the schema.
Yet again bits of hardware, 2 bolts that hold the heatsink to chassis loose
and wandering around inside the case, but probably just incidental to the
main problem.
I checked the switch in a can of water and it goes s/c at 86 degrees C and
reverts to normaly closed at 71 deg C and no amount of knocking will
disrupt it.
Logo - C followed by 2 square wave pulses
KSD301
K85 probably (smudged)
So the 85 means 85 deg C and perhaps K means NC
Bit low for a 2x 200W amp even if fan assisted cooling but as nc operation means
its immune to false triggering from contact corrosion I will leave that as is.
The unusual mustard yellow items that look like disc ceramic caps in
the ps are polyswitch fuses, marked T60 090 are 0.5 amp and 2 amp rating
according to the schematic .
I added a 90 deg n/o thermal sw to the
empty socket of the other channel bolted to the
underside of the heatsink.
Just a signal diode connecting the existing thermal sw to the
same pin on the other amp , empty socket, would have coupled both together
but I added a higher temp switch instead to allow half-cock continued but
still protected use on one amp should the other fail.
The rest of the protection is to protect from DC at the output, functional
in both amps. I accidently activated this by powering up with
one of the wires from the main bolt down bridge rectifier
disconnected.
The stray low current wire would seem to bridge back one side of the ps to
the other , on the same board, when they are both connected to main
reservoir cap common via large traces anyway - there was a lone socket pin
in the housing with matching frayed wire taking power to one amp , the other
end was with the power connector for the other amp.
I also replaced the 12V fan, with a 0.1A (
original unnecessarily overworked one 0.2A) as worn and wobbly and more to the point,
fully cut the casing open to give 5 sq ins vent area
at the fan vent and covered with a wire
grill. There was just 14 small slots with a combined area of only 1.5 sq
inches, let alone vortexing, so overloading the 3 inch diameter fan
with through ducted area of about 6 sq ins and so
losing cooling efficiency. Replaced the 12V
regulator just in case.
For the protect ccts, when in protect mode
the voltge across the base resistor of the relay driver pair
was 0.02V and .64V at the base and 0.76 V on the 12K resistor
In normal operation 3.6V across base resistor,
1.26V on base . Long term problem in one amp leaving
one Re o/c so on that power tranny the B-E "resistance"
was 109 ohm instead of 94 ohm measurement on
all the other 11 trannies.
Running lower amp (right) only and 8V , 400Hz (16W ) into 4 ohm
load with thermometer on the heatsink.
Stabilised to plus 17 deg C over anmmbient (with
this .1amp fan) after 20 minutes and .02V ac
drop in output. Star washers and
high temp glue on all internal bolts and
hotmelt glue on the connectors, especially
the small ones associated with fan and protect
ccts as little friction keeps them in.
Laney CD850S, 2002
Same as above plus broken effects 16 way Hex codeswitch, all plastic
Replaced with a proper metal one but greycode
so 1 to 16 became 1,2,4,3, 7,8,6,5, 13,14,16,15, 11,12,10,9
Laney CD850S
R ch intermittant "farty noise" and low level. Other times sometimes
low through one of the mixer channels L &R
4V pk -pk output and twizzling unseen section of the pa
then would drop clipped to 0.5V unipolar peak sections only.
The first splitter TO220 in the pa had a neat cold solder ring
around the base. As base , not current carrying then redid solder on all
tr on both channels.
With effects off and all knobs in mid position and 11mV, 400Hz
sine in each of the channels then -10dB bar graph LED just about
to light and L &R then op over 4 R
in range 3.4V to 5V ac (not as definitive posistion as all at maximum)
Por mixer channel was duff pad switch , surprising as doubled
up switch , so 2 chances to go wrong. Put a set on each central pin
to use different section of contacts. Not necessary
to remove bottom ps board to remove any of the mixer ch pcb.
Laney CK165 , probably 2003 combo
Buzz reported as pitched at a G an octave and a fourth below middle
so 100Hz. Both ps caps (2x 4700uF,63V) had oscillated to the point of breaking
the glue bonds. One had broken the trace and the other had
an internal fault. As could not find a sizewise replacement
and as very cramped anyway plus would have to tie them together
to (maybe) avoid a repeat. Replaced each with a pair
of 10,000uF, 35V with 12K balancing Rs, bolted to the
chassis between prea and pa, so 4 in total, and wired back to the pa/ps.
Uses SAP15 PO and NO, +/-49V
2x 560R, 3x 3.3K, 2x 10R, 2x 0.22R
ribbon 15,-15,0,sig,0,49V
10x 072
No name elbow speaker 1/4 jack had a loose barrel.
Undo the 2 screws , find a large nut that the tip
will sit in comfortably and squash , firmly held from
slipping, between tip and the central connection
to squash the barrel back to the flange.
Another time o/p fade
Speaker line measured 7k varying , bad spade connection , .5mm thick
spades. Or so I thought , amp bounced back.
Under the speaker dome, where the tails join the voice coil wire , under the black
lacquer, about 5mm diameter lump of nasty pastey solder broken into 2 parts ,
one bit on the tail and other on the coil wire end.
With scalpel cut half way round the dome, marking mid-cut point first at tails posistion.
Don't try cutting the join between cone and dome. Fold back the dome and cover the
voice coil section with a clean cover, held in place. Before melting back laquer with soldering
iron and scalpel blade. Refixed with tack-dabs of hotmelt string and then a good fillet run of hot melt.
Toned down with black felt tip pen.
Horn greater than 30Meg
Celestion truvox 1520 , 15 inch 8 ohm , 6.5R dvm
1kHz LCR 9.95 ohm and .728mH
Removed preamp and bad lead cropping disc at manufacture.
Ends of leads part cut through and bent over so easily move and wing and a prayer not touch
neaighbouring pins. Speaker screws are domed, cab ones are countersunk heads.
Laney GH50L, 1994
noise problems, crackly (pots) and rustling (valves)
4 presumably ECC83 (not originals) all test bad C/H leakage and
bad/ low or marginally good gain. Not a trace of any marking , as low power
valves, presumably no marking originally. They look like any other ECC83, no
bad cut metal/ broken mica or any other indication of bad manufacture.
5 controls needed seeing to gain,drive , master, bass and rear FX
pot, and seized knob grub screw dealt with
Laney GH100L
noisy
replaced one ECC83 and 2 gain controls
Laney HCM160B, 2003?
sp r/bk 5.8R
be/bn o/c , not used in this amp , the blue lead internally is connected to nothing on the prea
Return bypass cuts the amp
Bad HD2, maybe HD1
I/P so. , cain and enhance pots bad
B4K7 vol pot had been replaced badly by B47K , functioned ok though.
Graphic board retaining screws loose in nylon standoffs
10mV , 400Hz in , all controls mid and sw out
.88V ac over 8R load
Laney KB 30, 1993
Bad sound and loss of reverb on most of reverb level control
3x.47, 2x270R, 470, 2x BD909, 3x 072
Accutronics springline reverb SBB2C1b 192R/27R
zeners probably 2x 15V and 12V
Mains tr 76/2.1R
Splined pots 20K lin and 5k lin both worn out
marked HH 10.35-G8
speaker 6.1R
4BA top cab screws , slacken front grill screws a bit before inserting amp back
in cab
Laney L20H, 2007, PbF, valve amp
Intermittent loss of output and crackles.
Side-issue on polyswitches/ resetting fuses
Mustard yellow about 20 x 15mm , looks like a silver mica cap,
but round leads.
In line with about 2.5 amp valve heater line. Measures less than 0.1 ohm ,
apparently invariant to nearby soldering iron. .Letters China, 30, UF 600,
GL WE, polyswitch resettable fuse , like
http://www.datasheetarchive.com/download/?url=http%3A%2F%2Fwww.datasheetarchive.com%2Fpdf%2FDatasheet-052%2FDSA0059269.pdf
previous one I saw was marked UF250 and was about 8 x 8mm so not definite
indicator of rating, presumably that one had a 20V rating , on a 16V supply
30V rating and that Raychem series then package size goes with hold current
UF250 about 11x18mm, hold 2.5amp, long term trip current 4 amp
UF600 about 15x20mm , hold 6 amp, long term trip current 8 amp
UF900 ,the highest in that table 22x28mm , 9 amp hold, long term trip about
12 amp.
Some other polyswitch details
19.5mm marked logo of V over upturned V ( probably Tyco) 72, x250
HIQE China or EVAE Mexico
2.5 amp hold current , opens after 80 second with 4.5 amp,
> 3 min at 3 amp
7.5mm , logo B for maker and part BRN MF-R110
marked R110 5078S
1.1 amp hold current
Actually extensive PbF problems and poor 1/4 spade connections,
particularly at the choke.
Access - remove 2 rear pannels, 2 top screws, invert and then 4
side screws. Chassis not fully baxed so can tip over.
3 non pointed screws on rear cover
To get to the reverse side of the main pcb
which has the sm hidden TL072 opamps etc
leave fuse holder and remove the speaker outlet board.
Angle the pcb over the fuse holder ,
then pot array past the chassis rim, leave wiring in place.
10K, 56, 470R
2x 100R 1K
reverb measures 220 and 30R
+- 20V over 100R
264V,255V over 470R
255,220 over 10K
8.5V on 56R
Handle needed attention and mod, leather over cloth . If the metal
sections open out then the cloth can slip through the gap
and the leather stitching fail , so handle collapses.
Open out the metal to slide off, slide on a nylon tube
about 3/4 the whole gap length , then the end of the handle and then
close up. The metal would have to open to a 1/4 gap before
the nylon could slide off.
Laney LC15-110 , 2010 , owned from new for 1.5 years but no dating info found in amp
or on valves
N15039, RoHS etc , zener solder failing, all usual siolder suspect delt with.
Main problem was Hi input socket, jack needed to be pulled out slightly and
unreliably to use . This socket was also loose and earth continuity is via
the front panel for this socket. Socket was NA type enlarged on fault on tips files.
Low ip ground via thick black wire to amp, grounds via the ring not sleeves of jacks.
2x 10K, 470R 5W, 4x100R 2W, 6x 100K .5W
polysw 2x .9A, JK60,090
UF600, 6 amp
3x SMD TL072C
220R on o.p pcb
ewsolder D17,D18 scraping back traces
sp Celestion G10N-40 , 6.6R
Tank TPSB2BB3C1B R 208R, W 30R
Mains Tx 53R// Gy .1, or 28R, R 311R
op 107R/119R
Only the copious dollops of green lacquer were keeping the valve base pk in place.
Replaced with next gauge up in siize, restraining the metal from bending with plates
inserted through vent slots, and rotating screwdriver with minimum of insertion force.
Laney LC15R, 2002
Captive nut loose in the chassis blowing fuses etc
Blew one of the HT diodes and mains fuse
Some DVM resistance readings
speaker 5.7R
mains primary , 240V, 52.5R
secondary 206/19/19/188R
heater secondary 0.2R without valves
o/p transformer 104, 114R/ 0.5R
Laney LV100, 2010
intermittant output
Have to tilt the chassis so that the top of front panel clears the screws through
the cabinet corner brace plates, to remove chassis, just enough space
Speaker Celestion G12E-50 T5606A , 6R9 dc.
Fx return bypass sw cuts amp but HD3 connector had intermittant
on one of the IDC points. Removed closure , pared back each side every other one
wire sleeve and soldered to the IDC forks, hotmelted in closure for handling purposes
42V ac supply Tx 15.5R// .7R
2x 270, 150, .47R 3W
470 1W, 10R 2W
prea 10R 3W, 7805 4069 4x 072C
All mid , rev 0, sw out) 400Hz 0.096V in ,2.96V over 8R
Laney LV100 intermittant drop in power an no power LED
In clean ch with reverb up and 400Hz signal there is rythmic patterning
to the output, assumed to be normal, not springline
sp 7.0R
phones R sw carries sp current
.5V over power LED , touching brought
2.9V over and lit up, no obvious solder problem so replaced the LED
Canot see any clearance on tip sw contact of input socket and only a few
onces of pressure there will close the contact to ground. Replaced .
Laney R4, 2003
Bass Amp combo, 32 Kg, distorted breaking/muffled output, the distinctive sound of
complementary output failure of one waveform component, the positive
or the negative going one.
First thing to say is anyone finding one of these, put some fine mesh under
the top grill which lies directly over the power amp.
Kids like posting coins into slots, even TVs of 40 years ago
had such mesh under the ventilation slots. Perhaps
block off totally and add a vent or 2 at the
sides as there is no sides or top to the amp chassis.
A small piece of copper wire had dropped in this one
touching a couple of MPSA92, and half blown
the amp.
Uses 2 pairs of 5 pin SAP15NY and SAP15PY output devices
according to Sanken datasheet , in English,
h1-o03ea0-TR.pdf
150W, 15A, 160V bipolar with temp compensation.
There is another major flaw with the production of this amp.
The 4, 0.22 ohm ,emitter resistors are on end and one end soldered right
down to the board. Not failed soldering so 5W must be the right rating but
vibration is causing the resistor lead to progressively fail at the
juncture of the component side of the pcb and the flaring , over the lead,
of the ceramic covering of the resistor.
Replaced each with a pair of 0.1 ohm with a pair of ceramic beads
flat side against PCB and temperature resistant glue
holding in place.
As well as a mesh under the grill , cut an aluminium
sheet to form a sloping cover over the amp (so you can
tilt up the whole amp to slide in and out of the
wooden housing). Extended the 2 long stand-offs , leaving
a 38mm gap to the aluminium , and made brackets
to fix to the heatsink screws. Covered the leads to the thermal
switch. All nuts and bolts glued
in place.
Laney R4, 2002
Came in for replacing one of the input jack sockets.
Used a chassis mount,gold plated, wired tag one upside down
and cross-wired in.
2 of the output emitter resistors were
neatly loose, one for the N and one for the P
sections so output halved if he'd realised it.
Used 4 pairs of .1R and soldered eyelets to beef up the
standoffs and plaited some silicone sleeving to
make a rope to tie all the twisted lead joined Rs together tied
down to the board.
Laney R4 , 2003
No output
Failure of 2 transverse set emitter Rs so one
pair of devices still operational, not blown
due to overloading.
Bad solder on one of the main dropper Rs
Laney R4 , 2003
No output,
Failure of 2 transverse set emitter Rs so one
pair of devices still operational, not blown
due to overloading.
Bad solder on one of the main dropper Rs
exactly as the one above
The pair of emitter droppers width-ways across amp had failed.
Replaced with series pair of 0.1R with loop at top and
twisted rope of twisted triple of PTFE
as restraint.
Tx 3.9R // .5,.5 / .35,.35
Bad i/p socket solder joints
Laney RB6, 2005 or 2006
Farty noises, reported but not found on arrival or induced.
Poor central pin wiper contact inside the
"enhance" pot so intermittantly no ground connection.
Due to the bent pair of wipers not making good contact
with the conductive track.
Uses prea ,CA3080 , 5x 072 (SMD)m 2x 680R
PA, 2x 10R, 2x 0.22, 2 x SAP16
3 standoff + nuts on the pa board.
Beware of misplaced LEDs before refitting.
Pull the amp casing rearwards to give
enough room to disconnect the speaker connector.
Laney TF300, 2001
Phones output but no speaker, no hiss or sw on /off pops, blown speaker.
Drop in output , due to bad bypass switch/s, owner had compensated by upping the volume then fault "cured" itself
and surge blew the speaker. Getting into VC area mechanical failure of the wire , a break
in the middle turn of wire , furthest from pig tails. .23mm wire, 10mm wide 2 layers
probably. About 20mm of wire had parted from the former , still in place but forced
a break in the wire, from electromagnetic force or compounded by 3 of the speaker
mounting nuts were slack. No sign of any overheating, presumably the final straw that
broke the camel's back. Removed one turn , scraped tails with a scalpel, twisted together,
squashed with small pliers, soldered and cut excess with .5mm grinding disc
HH Invader 1001 41216, 6.3R
2 layers, 10mm wide VC, .23mm wire
All speaker current goes through phones bypass sw. Replaced that one and RET with inverted
and crossed tagged so.
SMD codes also see tips files for the ASCII 172 symbol
TS1 /2 , topcode 2D, SO682
TS5, 9BB, BC857B
I've never seen it before but seems quite sensible now I have
a likely treason.
5 amp rated TO3 mounted through heatsink and pcb. One C terminal just bolt
and nut , no electrical connection. The other is bolt , solder tag, star
washer and nut and the solder tag fully swathed in solder ,bolt hole to
wiring hole , merging with thick pcb trace, but only requiring to pass 5amp.
I can see that star washer could punch through the thin copper on the pcb so
this method avoids that potential problem, and would constitute good
practice assembly
Curiouser and curioser. There is a black "washer" between tag and pcb pad.
Undoing a bolt this was a standard black nylon TO3 mounting insulated washer
but on the underside. So instead of bolt head, insulator washer, TO3 flange,
mica, heatsink, pcb it is bolt head, flange , mica, heatsink, pcb, pcb and
trace, TO3 insulator upside down, solder tag, star washer, nut. Flange is
same thickness as pcb and nylon insulator is only long enough to half
penetrate the pcb so what advantage ? or cock-up?
But an insulator ? I reckon cockup , myself included. I should have said
plain cylinder insulator set solely in the heatsink hole rather than necked
washer under the head, or there would be no electrical connection to the TO3
flange .
ISTM the main problem with this arrangement of bolting through pcb is
compression of the polyester/glass of the pcb. Another amp in yesterday had
a nut bouncing around inside causing mayhem. Just a 3mm nut with star washer
for holding pcb via standoff spacer to chassis. Or was, until pcb
compression and vibration. Personally ,in non hot areas, I prefer star
washer and nut with nail varnish , or a nylock nut. I'm not convinced that
the radial edges of spring washers is enough to stop vibration induced
undoing , combined with plastic pcb material.
Tightened the TO3 fixings, leaving the solder tag arrangement in place.
Bad valve seating in socket. Cut away the heatshrink, as no dimple etc on the socket ,
not doing anything. Silicone sleeve tied off through pcb hole and chassis hole with
a loop around the pip of the valve, in direction to self-lock in place
Springline 25.5R, 207R
Laney VC30 , later than 2004 probably 2007, ser no in 1200s
But seemingly not PbF
Usual suspects, even though only 2 years old probably. But final straw was
mains fuse blowing at switch on, no major problems on previous use.
Consumption max 100mA rating plate says and 1.6A antisurge for 115V use and
630mA antisurge for here , 230V use , toroidal transformer. Owner did not
chuck the fuse and it is only just blown , ie just a small patch of slight
spray of white dust/smoke on the glass at the break so little more than
mechanical failure. Assuming nothing else found after taking the amp to bits
, replace with 630mA and advise the owner to be prepared to change the fuse
every year or so ? , or uprate to 800mA antisurge.
Methinking 500mA to 630mA is not enough margin for toroidal and normal
switch on surge, no thermistor in schematic or actual, schematic that I have
shows 830mA for the 1995 version. Changed to 800mA with note on plate
Incidentally the loud thumping noise in these , on movement , is the
springlines knocking the cardboard closure and the cardboard acts as a
speaker cone. They do not bang against the metal side. Placed a couple of
daisy chained large cable ties around the middle so bowing outwards,
with some silicone sleeving over
as soft then cardboard cover, Coils 215R and 16R.
The reverb tank , as usual, is made to be screwed to a cab with soft rubber
grommets. I suppose someone decades ago realised that putting them in a
cloth bag acoustically decoupled better, hence having to close off the open
side with whatever was at hand.
Nasty sharp metal guillotined corners need filing back.
Mains tr primary 20R
Bad exit elbow jack, bent up central tag a bit and a twist of
nichrome wire around and under and tightened while the pin
is squashed axially , over half cap and tip, in an engineer's cramp.
Bad spade connectors
on IEC and elsewhere. Poor fuse contacts on 20mm holders,
Usual suspect solder points under main
board, remove the rocker switches to angle
up this board for access. 8R speaker
EL84 s despite measuring CH/R of 25 to 35 Meg were giving
a noticible amount of flutter/rustle (with all controls ACW)
Laney World Series WS100SC, 1993
Could hardly use from various crackles and bangs.
Loose speaker wire , one source.
Treble controls on both ch take signal throughput via wiper so when worn and broken then so signal passes.
Many Alpha pot switches for gain/vol pots worn needed reconditioning as per tips files.
Bad input so solder
For chorus on both outputs , need a patch lead between both Slave/DI sockets apparently
BR1 heatsink can turn to touch fuse holders
Speakers 2.7 and 3.1R different printing on labels both HH one 12 60 64 the other 2 60 64 and 1993 datecode
Tank 8BB2C1B 27R, red 205R when repaired , broken lead at bend around the former of the coil
not at the phono socket unusually
Tx 13.6R // /6R
LD Systems DJ200 Wild Thang (sic) WildThang ?, 2007
Just out of warranty - distortion on one channel and crackles. One sense
trace (unipolar) excursions only on that channel, expecting blown o/p transistors but
all now check out ok. Output undistorted until about 0.8V pk-pk ,
there was about 0.4V DC on those 5W resistors. They are all buried under the heatsink , so needs
taking apart to monitor.
Expecting bad solder, RoHS, as solder joints looking like 20 yearold leaded
solder joints.
No bad solder found - bad layout design. The end of a low power +B wire link
ends exactly under a 3.3K 1/4W resistor laying right over it, so touching
the bend of the wire. Nothing visibly wrong when received but maybe
overheating of a 470R R19 resistor at a TO92 Q7 emitter. Expecting bad
solder I started tapping things and phut this insignificant 3.3K , R5 at the
collector of a TO92 Q1 burns up. I'm assuming its 3.3K as that was remnant
measurement and corresponding channel B is 3.3K. Both these separated
resistors are electrically connected in the low power section of the amp and
it was the final straw.
According to the owner the amp had been overdriven for too long , outdoors,
but no sign of that but perhaps enough general heat to flex something.
So for these amps bend any resistor away from the ends of any wire links.
2x 470, 4x 4.7R, 8x .25R, NE5532
2SC2073, 2SA940 / 2SA1943, 2SC5200
+/-55V , +/_14.6V
2 x PROT light when protection th sw activated
No threadlocking on any pcb screws
Fan action questionable, failed tapping test so replaced
both pcb plugs and sockets with soldering
Fan disconnected , 400Hz , 0.15V in and max vol, gave on one channel
nearest fan sw,
5.64V ac over 4R, 23 minutes to raise 34 deg C over ambient,
still rising 0.5 deg per min when cancelled test no change in o/p level
over test period.
With fan reconnected 0.2V, 400Hz in , 1/2 vol
and 3.54V over 4R, fan cut in at 33 degree C monitoring
with thermometer laying over fins with end and top covers removed.
With no I/P , or speaker and 1/2 "vol"
On one channel , bank of Rs at fuse end of pcb, approx Vs
-57,0,20,0,-20,0
at 0.25Rs ends of other bank
-56,0,-55,-55,0,55,0,56
Thermal switches marked VDE KSD 301
2 of this make and type? on power amp heatsink with no other markings other
than moulded numbers on the black housing, so unlikely to indicate temp etc.
One marked 23 is n/o , to activate fan but seems rather high click over temp
(soldering iron activation), temp not actually measured yet.
The other is n/c marked 14, overall cutout
Anyone know how to decode these mould marks assuming they do relate to
temp/type or any other ideas?
If I was designing amps ~ I would only use normaly closed switches as
failure mode is usually o/c or high impedance plus each of these use 2 pairs
of connectors in line back to solder points I would choose fails safe mode.
Fan one tested higher than I would have thought but as usually only used at
low power , will leave unchanged
Fan one cuts in at 68 degree C and out at 45 degree, checked up and down
twice for reduced "hysteresis"
overall cutout one goes o/c at 90 C and s/c at 60 C
LEEM KA1210, 1998
Bad sockets
sp 6R6
Tx 12.2/.8 r-r
No name 1/4 inch jack sockets
First time I've come across non-standard pinning. Moving contact and static
contacts swapped over. Came in because the bushes were breaking off at the
body .
Replaced all 6 and then had to wire them in reversed. Anyone know other
makes where there are such booby-traps , so can be forewarned about
Maybe company CHS/CH5? the phones outlet with double isolated C/O switching
style had the same failing, that one marked with that logo.
pinning is
1
8745
6326
1 gnd, 3 ring, 2 tip
5c,4 n/c, 6 n/o
8 c, 7 n/c, 6 n/o
(maybe confused with Wave W500 amp done at the same time)
Used the standard 1/4 in socket to isolated sw conversion, ITF
Tank R out 202R, W 2,6R
16-2.2K
Line 6 Spider 3 amp with RoHS and PbF markings all over, date only 2008
no abusive use/speaker/lead problem. The boards are obviously PbF , white
deposit as though been in a damp shed for 10 years. That is except for the
interboard ribbon soldering. Boards populated and soldered in China with PbF
solder and assembled in USA with leaded-solder or 2 flavours of PbF solder,
one goes white easily and the other stays shiney?
TDA7293 failed , going by burnt off lacquer on the minor trace between
power - supply and signal - supply , then failure in signal half of the amp.
Final failure was sub-ohm connection between +,- and output pin and about 40
ohm to ground. If there had been intermittant contact to a pin due to PBf ,
could that knock out a hybrid? Tugging on dropper Rs etc has not shown any
so-elucidated poor joints on the rest of the board and no PbF part-ring
cracks seen.
Unlikely joint failure at the pins as they are set in ring-barb hank bushes.
Monolithic, not hybrid, I decided to crack this one open , not much to see
other than smoke staining and strong smell of smoke.
I reckon it was probably slack h/s clamp. Although not noticably loose on
undoing, there is no permanent deformation of the silipad on this one
(unlike its companion TDA). Clamp is 3:1 ratio cantilever U section steel,
ratio the wrong way and no star washer or equivalent under the retaining
bolt heads
Rotate to remove chassis from top slot of cab , careful of the proud and vulnerable
lower plastic lip then and in general handling.
2A mains fuse black and absent remnant of wire.
Tx 6.5R//0.6R,6.5R/ red .4R / Blue .5,/5R
In broken state about 1R between +&- mrails at the TDA7293
40R gnd to +&- on U2
40R gnd to +&- and o/p on U1
U1 op about 1R to + &- rails
LM1806, 7805, LM317T
4x .47R, 2x 2.2R, 1.2K on ps
2x multi 20K DIP R CTS? as 4 x 10K R2 and R10
R1,R9 1693 marking
R14,R15 103 marking
+/-47V , 5.3V ac ,34-0-34V ac
Beware 1mm ring barb hank bush pcb seatings for the TDA pins ,
probably best to cut the pins before removing the IC
Beware T slotted nuts for heatsink clamps and centre anchor.
In reassembly tighten nut and bolt and clamp at top of slot holding with
bolt screwed tight to rear of slot and then when in posistion mover the clamps
in true place and tighten. Remove the heatsink from the chassis for this and disassembly.
Burnt varnish over trace between pb and p15 of TDA but no burnt traces
Replaced with new , low variac powering there was -rail voltage at op.
Under the DIL R2(p13,p14) package there must have been a burnt trace had to bridge with wire
from pins to nearby SM C3. Lack of feedback from o/p to ip pin , compare
with the good TDA. Should be 10K between p2 and p12
400Hz .1V ac in Clean , low,mid,mid,mid,off
off , off , mid, master mid
B ch , 1 &2 op 8.4V ac with no speaker loads
4&5 .12V ac , 7,8 .12V, 6 3.2V, 9 -47V, 12 +48V on ribbon
Line6 amp repair, Spider 111 30, 2006, or even spide 3 30
Speaker hiss so the TDA2050 ok, +/-20V. +/-9V and 3.3V for the digital all there. No front LEDs lit
There was some throughput of hum when I first connected a jack to the input but nothing since , nor feeding test signal direct into the 2 lines from the 072 first opamp , conveniently discretely isolated on that end of the board. I've been bench testing without the connection to the front panel click switches+LEDs, to avoid taking all that part. Next thing to try, but anyone know if a break in that ribbon to the front panel , or my full disconnection, can cause the Philips system uC to stop functioning, by lack of load or continuity?
probably something to do with 3 very iffy looking chassis ground contacts at the 3 front panel sockets, will wire between them and see how things pan out. May even need a footswitch connected to the amp to do anything.
3 ground contacts bridged, no difference.
Probably like Roland Cube pot problems. All pots except the master , are used as digital controls, 0 and 3.3V dc on the ends. Amazingly only one of the 7 "digital" pots you can turn down to a few ohms , all others many DVM-R ,Ks to megs and wavering. As there is polling signals on the front panel switches the main uC must be ok , for that anyway, and I assume there must be a control logic that locks out the whole system if the ADC voltages are wavering about , beyond some set minimum for the user doing an adjustment of one perhaps at a time
Replaced the worst 2 pots with fairly stable minimum few 100s of ohms settings of the rest, no LEDs.
I'm now assuming the inbuilt flash memory of the
P89LPC936F is corrupted as distinct from the RAMs. There is a vacant header for in-cct programming with RST on the overlay. This line goes to the INV-RST pin of the uC and according to the datasheet a LOW on there will reset the uC, but no change still no LEDs. It looks as though to erase the flash , needs a Chip Erase command via in-cct programming, so that looks like the end of this usual digital farting about. One more effort ,Cannot find "factory reset" for Line6 spider stuff, will try 5 seconds on each at power-up and then 2/3/4 of the adjascent ones.
Factory reset
Hold Clean channel button and power on.
, still dead so some other problem perhaps. I can see why no audio throughput. The AK4552 audio ADC\DAC is held off at p13 by the big DSP which presumably is held dead by the system uC. Its times like this that I feel there is something dead simple, for just a bit of inside gen. I think I'll rassemble in the chassis , perhaps there is some hidden ground plane that connects to one of the fixing points.
As there was some audio for half a second on first connecting an input there cannot be something permanently failed
Wasted too much time on this. Annoying as the datasheets are available for all chippery, including the DSP and a serial flash memory so 2 distributed memory and 2or 3 on the uC.
What I thought was polling of the front switches was floating lines to the uC, they never get committed to an input or output state, oscillator is fine .
If there is a strong signal on the input then at powerup or powerdown some low output for half a second, explains the initial hum signal heard.
There is a mute line, to pin91 , GPIO(0) overlay labelled "guitar sense" grounded if no jack inserted
TDA2050. Red 6.3Vac , blue wires 31V ac
With TDA undone add a heatsink for testing purposes.
Remove bush nuts, slide pcb 1 inch to release
power conn. Beware of small ribbon to front sw/LED panel
+/-9V on marked pads via Q1 and Q2
SMD marked k2T and k2X
pass Qs via SMR droppers 100R R54/R61
from HI+ and HI- rails
C31/C32 caps
HI rails +/-20V
+/-9V and 3.3V ok
3.3V on U6 74HC and p89lpc936f
HCU04
74HC14
DSPB56364af100 j25d
No polling of sw panel, just floating voltages
SDA,SCL go to D3&D12 on front so not I2C
AK4552 p6 DEM0 0
p7 DEM1 1
p15 Lout
p16 Rout
p13 H for normal operation
Guitar sense/mute? is from the 1/4 in ground sw
Italic T that looks like a 7
SST27VF512
Varying signals on front panel ribbon but no 0V and no sc connection to gnd
Footsw control lines go to U6 p5 and p12
RJ45 p1 and p3 gnd, p5 to 6.9V
VL+ and 3.3VR supply
U9 p5 to signal to TDA2050
RST on U3 goes to front PCB D6 and p6 of uC and open J2
RXD/TXD at H3 go to uC p17 and p6 is not-RST
Line6 amp repair, Spider 3 30, 2006
Speaker hiss so the TDA2050 ok, +/-20V. +/-9V and 3.3V for the digital all there. No front LEDs lit
There was some throughput of hum when I first connected a jack to the input but nothing since , nor feeding test signal direct into the 2 lines from the 072 first opamp , conveniently discretely isolated on that end of the board. I've been bench testing without the connection to the front panel click switches+LEDs, to avoid taking all that part. Next thing to try, but anyone know if a break in that ribbon to the front panel , or my full disconnection, can cause the Philips system uC to stop functioning, by lack of load or continuity?
probably something to do with 3 very iffy looking chassis ground contacts at the 3 front panel sockets, will wire between them and see how things pan out. May even need a footswitch connected to the amp to do anything.
3 ground contacts bridged, no difference.
Probably like Roland Cube pot problems. All pots except the master , are used as digital controls, 0 and 3.3V dc on the ends. Amazingly only one of the 7 "digital" pots you can turn down to a few ohms , all others many DVM-R ,Ks to megs and wavering. As there is polling signals on the front panel switches the main uC must be ok , for that anyway, and I assume there must be a control logic that locks out the whole system if the ADC voltages are wavering about , beyond some set minimum for the user doing an adjustment of one perhaps at a time
Replaced the worst 2 pots with fairly stable minimum few 100s of ohms settings of the rest, no LEDs.
I'm now assuming the inbuilt flash memory of the
P89LPC936F is corrupted as distinct from the RAMs. There is a vacant header for in-cct programming with RST on the overlay. This line goes to the INV-RST pin of the uC and according to the datasheet a LOW on there will reset the uC, but no change still no LEDs. It looks as though to erase the flash , needs a Chip Erase command via in-cct programming, so that looks like the end of this usual digital farting about. One more effort ,Cannot find "factory reset" for Line6 spider stuff, will try 5 seconds on each at power-up and then 2/3/4 of the adjascent ones.
Hold Clean channel button and power on, still dead so some other problem perhaps. I can see why no audio throughput. The AK4552 audio ADC\DAC is held off at p13 by the big DSP which presumably is held dead by the system uC. Its times like this that I feel there is something dead simple, for just a bit of inside gen. I think I'll rassemble in the chassis , perhaps there is some hidden ground plane that connects to one of the fixing points.
As there was some audio for half a second on first connecting an input there cannot be something permanently failed
Wasted too much time on this. Annoying as the datasheets are available for all chippery, including the DSP and a serial flash memory so 2 distributed memory and 2or 3 on the uC.
What I thought was polling of the front switches was floating lines to the uC, they never get committed to an input or output state, oscillator is fine .
If there is a strong signal on the input then at powerup or powerdown some low output for half a second, explains the initial hum signal heard.
There is a mute line, to pin91 , GPIO(0) overlay labelled "guitar sense" grounded if no jack inserted
Logic3 TX101 powered speaker, 2007 , RoHS
frayed mains lead, exposed wires, at cable entry.
Cut hole for IEC so, see tips
Tx 10-0-10/ 15-0-15
TP2804HPN ,7805, AMS117 4 pin SMD, ground off controller,
3x4558, 5340CZZ, CS8415A
pa F4558 5 pin op D2050 , D2030A devices
large 4R speaker 3.6R in cct
Powered speaker works fine with clean audio feed but get it connected to the
audio out of the owner's laptop and it drops into some undefined error mode
killing the speaker output and display/,switch off, restart and repeats.
The powered speaker has an unused MP3 connection and tuner and laptop has
wifi etc, unused for audio feed. I suspect some sort of RF is being
conducted down the audio leads. Other than passing 2 or 3 turns through a
ferrite ring .
Its a bouncing "repair". Just needed the mains cable replacing but as it is
transported in a box , cable frayed at fixed cable entry. Replaced with an
IEC socket which of course required the metal panel on the rear to be bonded
to ground. Since then this problem, no problem before. The earthed metal
plate is now acting as an RF collector/ reflector or something. I'll have to
also find out if he uses a long extension power lead to this , used in a
hall.
15 speakers. Front foam cover pulls off , 8 screw heads go into plastic cups.
Don't drop screws in the vent holes, mack off. Allen key to remove the 8 modified sc
All sp have foam suspension so perishable?
Pull glossy front panel away , pull ribbon from black gummy glue by the ribbon not at the
solder points
2x 4052 at aux i/p and co-ax
bad solder pin 11 via 4k7
1 aux i/p but via 47uF to p4 via 47K , both terminated by 47K
FM tuner YSJ939- F5U2-R 707071 00590
H/S is connected to main pcb standoff bracket connected via screws to back plate only
black paint holding off connection. Capacitive coupling of RF?
Disconnected the earth to the back plate back to its origional square in squre declared
double insulated status and amp stopped bouncing back
Luxtrack Tootsy 2 lighting sequencer
No function after being dropped.
The mains transformer for the logic is pcb mount type so
shock loading had snapped one of the primary wires near
the mounting pin.This equipment failed earth-bond safety test.
Only the top panel is bonded to mains earth and as it is black
anodised (hence insulated)and other panels are not separately bonded
so added bonding. Also safety-wise in use the angle Ali heatsink
is not firmly held and could flop into touching the chassis. Cover this
area of chassis with suitable insulating sheet material.
It is too easy just bending the Ali heatsink to get
at the drivers area - don't do so, as the pins of the triacs will fracture with
age hardening / vibration. Undo each screw mount to remove h/s.
For a tighter job remove each triac and push thru pcb pins soldered into
place and solder lengths of triac legs to these pins.
Mackie CR1604-VLZ 16 channel mixer , 1996
No tape insert inputs and had been used on 240V .
Tied the IEC line socket to the mixer IEC chassis plug
with a label with large letters saying 120V, The other end
of that lead is US plug for the 240V to 120V auto transformer.
Unusually, setup for rack mounting so the "back-plate"
has upside down and reversed legends.
Back plate has loads of active on it SM 4560 and trannies,
the 20 way ribbon probably relates to the tape/in + others.
The steel plate is held by 2 torx screws from the inside so you
have to remove all the bush-nuts and XLR screws.
ps has 2 x 5.6R, 2 x TIP29C, 317 and 337 set for +-15V via 130R.
ps outs -15,0,15,-15,0,15,47 and floating 18V on the spade connectors
presumably dropping to 12V on load for the lamp.
One +-15 for the 4560s and one for the 2601 bar-graph,
zener has 48V across it. Replaced the 317 as had overheated.
Problem with the 20 way ribbon cable. Once again a piece of
expensive kit that does not have shrouded indirect
"edge connector" headers so easy to place the socket out
of register with the header, especially one line connected
to wrong line and one line unconnected.
Ribbon leads' red is not a consistent identifier, Red on 40 ways is
pin 40,red on 20 and 26 way is pin 1 , where marked on board.
pins 18 and 20 of 20 way via 120 ohm to Main Outs
24 ,26 on 26 way via 120R to CR Outs
13,16 on 20 way to main fader top points
Middle 40 way +15V on 38,39 +37
40 Way nearest Tape in/outs -15V on 2,4,3 remaining odds tend to be grounds
Uses approx 15 off 4560 dual op-amps on rear panel
and about 75 on main board
plus 2 SIL 4560 for headphone amp and 8 2901 quad comparators for
bar graph. The 8 pole 2 way relay marked on the user manual
block diagram for SOLO LEDs and signal routing
is probably numerous 4560 as gates.
Using phones socket outside of chassis needs earth connection.
Push RL buttons on each channel to pass feed through to
main mixer. To reassemble rear section. Fix the pcb to the steel plate
and then connect that to the rear plate. Feed cables through the
plate with the long slot and screw through the ali of the ps into
the fixing boss on the middle of that plate. Then introduce
the 2 parts together and screw the power entry plate to
the backplate only at that stage. Machine screws for the
Al to Al casing and tapered screws for the XLR sockets.
Mackie ProFX12 , a couple of years old.
OK at soundcheck, but failed in first use proper. Owner retained one XLR feed and used a 1/4 inch line for the other channel and continued.
With me checks out fine. Now the double XLR boards has that style of soldering , pin and cup?, where the end of the pin is enveloped in solder. Then as 4 closely spaced pins for the XLR difficult to check by flexing. Will try tomorrow with proper continuity check on all pins. I've seen this failure before , but I don't think with proper solder. Does PbF expand on cooling and so the cup helps to break contact, more than just a ring of solder, or just cold-solder joint failuredue to thick + long pins so substantial heatsinking.
At the moment no sign of any solder sweated thru the presumably plated holes to the component side of the pcb, "nice" clean gold finish, suggestive of inadequate heating at soldering.
Hopefully a pbf problem on that rear board and not balanced line feed buffer amp failure , requires removing all the top panel hardware.
a pic of the "pin and cups"
http://www.diverse.4mg.com/mackie_pbf.jpg
I wonder if there is a significance to the sharp deliniation between the mirror finish of the cup part and the maculate finish of the sleeve part. Indicative of differential cold-shocking while cooling ?
I'd not thought about that, will have to test the bypass breaking force etc on the Inserts. So fixated on trying to prove a PbF touching contact. I'd liked to have seen movement or measured 10 ohm or more , consistently somewhere
The 2 break situation is consistent with the following sorry saga, perhaps, but I've concentrated on one "solder" joint, could be one regularly bad and sometimes its mate goes bad. A regular 3db could easily be masked by unmatched sliders or something.
Picked up the board this morning and first contact I went to measured 40 to 60 Kohms, tried the rest and .5R or so. Returned to the first and similar .5r now, so has the contact remade or was it oxidised/dirty contact related to my first DVM reading.
Felt-tipped the exposed pin/standoffs and flexed the pcb and no shifting seen .
Soldered a good contact away from the first suspect joint and fitted a proper XLR into the socket , to make good DVM monitoring points.
All measured .5R or so and tended to reduce a bit on heating the pcb to 50 deg C or so and increase to 1.5 ohm or so on freezer spraying the extender parts of the pins.
So suspicious but not conclusive . Tried the first contact with passing 3 amp through it , as no active stuff on this board. Dropped just 20mV at the contact. Returning to DVM-R and now it was .1R or so , but increasing to .5R or so on pcb low-level heating.
Decided to grind off the cups of the solder joints , bite by bite , to avoid melting solder. Again tried twisting the pcb and deflecting and no movement seen between the brass and the solder .
I desoldered the 2 ground pins. Then tried just finger pressure to pull out the remaining pins. I assume from my previous twisting, or maybe from being bashed in use at some time. The brass pins failed.
These are 1.6mm diameter and the pcb holes are for that size. But these Neutrik XLR would seem to be made for old-style hand-wiring then solder, not pcb use. There is a turned recess ring on each pin, down to 1mm diameter, to take a loop or twist of wire before soldering.
This recess is the thickness of the pcb. With the pins sheared off now and the remnant stubs still in the pcb , you can see that no solder at all has passed into the .3mm gap around the pins. So in effect the 3 main pins (not the frame ground pin) are only "surface mount" soldered , not through-board soldered, so mechanically weak joints regardless of use of PbF.
The shoulder length of the frame ground pin is right for pcb mounting, so are these recessed pins intended for pcb with eyelets , but not used here, or for handwiring?
I cannot find an exact image of them
http://www.mondospettacoli.it/shop/index.php?main_page=popup_image&pID=6854
is the nearest long standoffs, is the distant ends of the pins, in that image, eyelets near the ends
no bypass contacts on insert mode. They've skimped on having no MUTE reminder LEDs per channel and one under the bargraph that mutes the whole lot, unLEDed, just where you would unknowingly push it on handling the mixer, 10 minutes wasted there
Mackie SRM450, late 2005
Slight mild distortion on mid frequencies, really only noticable when comparing
with its fellow.
Line +40dB level LED on , increase level to NORMAL and LED goes out.
All 12 inch sp bolts were loose by about half a turn , except one , probably significantly
as al would have dropped out if all were loose.
Low Frequency and High Frequency amps are not identical so cannot be swapped over
for testing purposes
All main active had relatively loose retaining screws, 1/4 to 1/2 turn needed ,
added lacquer to them all , I know not high temp, but these cup sprung washers don't
have and edges like star or cut ring washers to stop them turning, may just be compression of the
insulated washers of course.
Mackie SRM450, year 2000
Horn output but no bass output.
Had intermittently broken output and then
one time of powering up, nothing
Acces the bass speaker through the front grill
not by separating the main body halves.
Cutting away the cone the break was at the point
where the round form of the voice coil was joined/
deformed to make the flat ribbon to go axial to join
up with the braids. Looks like a design flaw the copper
wire is pressed to form the axial tails so a stress point
there. Also the coarse grill on the magnet end would
allow degrading foam particles to pump in and
out, really needs a pair of large hemisphere
grills one inside the other with fine filter
between properly. VC dimensions of the Mackie M1263W
2x 90 turns covering 15mm length, 63.5mm ID of core,
thickness with 2x coilwire , 0.9mm
Device listings in order
power
IRFP9140, B817,B940a,C1567
D1264a,D1047,IRFP150N
677F070,B817,B940A,C1567,
D1264A,D1047,MJE295,MJE3055T
signal
c3788,A1478,JE340,JE350
loads of 4560, 1x 4566, LM339M,1x 2068
2x .22, 2x .12, 2x 2.2, 2x20, 2x .22
Mackie SRM450, year 2004
No abuse but failure of horn tweater
First problem how to part the 2 main sections
of the cab to get to the horn. P/N 0008093
Heated screwdriver as per tips file
Drilled out the screw holes a bit for easier
assembly/ next disassembly , (will add star washers under heads)
Caproic smell came off - what do Americans use as
glue or filler for construction plastic ?
I only smell it with USA equipment.
These Mackie screws, 17 of them, (2 slightly shorter either side of the bass
driver) , in my opinion , are bordering on the threshold of shearing without
such heating, they deliberately used undersized holes probably.
So the second of 2 Mackie SRM450 to have mechanically
broken tail at the voice coil. 25 turns of about 0.07 mm
silver wire over about 1.75 mm .
Previous , different unit the one above in this file, bass driver coil broken
where the coil wire is deformed to flat for the tail.
Not the slightest trace of overheating on that one.
This one, horn , nearly at this tail juncture , the break marked B
below, half turn vroken away from the resin core, and again so trace of
overheating anywhere.
http://home.graffiti.net/diverse:graffiti.net/mackie_horn1.jpg
4 engineering bolts hold the diaphragm to the magnet
but it is set in plastic frame, although engineering plastic, presumably
can deform enough to catch something.
As there is a milled out recess R already there I intend
trying to take the + and - tails through the same
side, not diametric. Grinding a slot in the
aluminium ring to take some 3x3 plaited 46 swg wire as tail.
Replacement driver 130 USD , diaphragm 70 USD
so worth trying as presumably swap USD for GBP and
add some for here. Very little diaphragm movement
so should not foul anything.
http://home.graffiti.net/diverse:graffiti.net/mackie_horn2.jpg
http://home.graffiti.net/diverse:graffiti.net/mackie_horn3.jpg
http://home.graffiti.net/diverse:graffiti.net/mackie_horn4.jpg
Cone thing presumably just stuck to the metal,
fell away on removing the horn part.
So it may be an effect of work hardening , relative increase in the effect
of imperfections/micro fractures or some other metallurgical effect.
Mackie speaker voice coil failures due to this flattening/ribboning process
to make the tails to the outside world.
Previous failure at the juncture of round to flat (0.07mm round to about
0.02 x 0.2mm) so at the peak stress point.
This one along the length of the ribbon section, but the whole 50mm or so
run was brittleised and disintegrated on touch, not the slightest sign of
overheating on the remaining 25 turns of round wire.
broken end marked B on this pic
Cannot expore the metallurgy as that curve of "wire" as totally
disintegrated to dust.
Thought I could solder to remnant and lead in
and lead out on the same point, not diametric
opposite. But required grinding a slot in the aluminium
disc. Doing it in situ with the burr action the
wrong way and scudded into the voice coil.
Had to replace with an APT horn 85W (6.2R), as much cheaper
than Mackie and those are proven suspect anyway.
Mounted the APT80 bodged with spacer and washers etc as
holes don't line up with Mackie horn section.
Added 1 12V, 21W bulb in series as a bit under-rated
Threadlock on the horn bolts so heat well before
undoing. Bass speaker , yellow leads /
horn blue.
Tx 5.1R // 0.5,0.5 / 1.0,1.0R
2x 0.22R, 2x 20R, 2x .22 5W
2 x .22 , 2x 2.2K
With normal gain set, low cut in and contour out.
17mV input , for 400 Hz, .49V ac over bass and 0.001 V ac over horn
for 4 Khz, 17 mV, 0.012 mV over bass and .2V over horn
Assuming same power devices and postions as the SRM450 above,
not confirmed.
for the 4KHz input and voltages left to right along "horn" strip
14.4,0 / -.56,-43, 0 / 0, -43, -.56 dc
-1.2,1.2,-.55 / 0,43, .55 / .55 , 43, 0
-15.1,-43,-14.6, 15.2, 42, 14.6
for 400 Hz and "bass" strip dc
-42, -88, -42.8 / -.56, 43, 0
-1.2, -42.8, -.55 / -1.2,1.2, -.55
1.2,42, .57 / .57, 42,0 / 41, 87, 42
It may be possible to swap output devices from horn
side to bass side and replace the horn ones with lower
spec devices, if pushed.
Bass amp is Class G,
the higher voltages are switched in with the power Fets.
Before wrapping up a Mackie SRM450 powered speaker I took some
representative DC voltages on the complementary pair power devices of the
bass driver amp, for me and all else, future reference.
-42, -88, -42.8
41.2, 88, 42
in comparison for horn side amp, same devices
0, -43, -.55
.55 , 43, 0
Probably class G.
I don't have the schematic or even saw the track-side of the Mackie board
but that explains the presence of power FETs
Manacor miniature 8 channel mixer.
No output on either output
There is no reverse 9V protection so it is easy to change battery
with unit on ,touching battery terminals the wrong way and knocking
out both LA3210 SIL op-amps so replaced
also add 1N4001 in supply line to on-off switch.
Mark Bass Combo Head, CMD 121H, of 2005
Little Mark II on the prea pcb
After half an hour of use a loud consistent pitch , low frequency buzz
Proper solder, from what I've tested .
Mark Bass/ UK have "repaired" this before, changing the tweeter. Even the
owner knows this is bollocks as he has a recording of the buzz from the main
speaker, before and after that "repair" .
I've heard it and if it was a conventional power supply I would have said it
was a loose main rail electrolytic or bridge rect and consequental 150 Hz
buzz (uk mains of 50 Hz).
I've heard this recording but have not been able to measure the frequency ,
so may not be 150 Hz.
Of course now its out of the cab and opened out on the bench, no problem
with it, with dummy load, directed hot air over PS/PA and PREA and
"twizzling"/ targetted wrenching. Not brought out the big-gun yet, engraving
tool with nylon active end , and headphones (because of horrendous noise)
monitoring of output.
But as a thought experiment. What sort of fault in a SMPS amp could produce
such a 150 Hz buzz? Anyone ever known a problem with the HV DC to the SMPS
producing interference on the PA rails?
When its occured with the owner , no amount of kicking the cab would make it
stop or even change character. I will have to check with him if the buzz is
total or buzz over the guitar output as recording by owner was obviously not
playing at the time. And try and get a sound file / copy of his recording to
measure the f
ps
the ident of the SMPS driver is ground off , as per usual , it would seem
Attacked with engraver and from that , can't imagine the G-forces involved,
passed A1. Whenever I do this with other amps there is always some
microphony showing up with one or more capacitors, but not with this amp.
But...
some things that are not right, if not actually wrong.
The main ps heatsink that carries the switching transistors, has two VR 7812
and 7815 with uninsulated tabs. The second pin of each is taken to ps ground
but also via the tabs and one Allen bolt fixing to the ps ground. Well it
would if not loosened to finger tight , requiring 1.5 turns to tighten. The
other fixing bolt is not bonded. Could some high frequency be induced in the
h/s just by proximity/miniscule leakage of those transistors and affect the
regulator/s ?
The 2 mains caps 200V, 1000uF are 105 deg C Kendeil and measure excellent ESR and C
cold and hot, but one is slightly domed in comparison to the other. Waving hot air
around introduced a reverse image of Mercedes 3-legged logo, somehow, ie raised
reflecting weakened slots underneath presumably. These
caps have ant-vibration mechanical cross bonding to each other with hightemp
hot melt but also fixed and so thermally connected to this heatsink. I can
see that bridge being cut away . Could a problem in one of those caps cause
the owner-observed fault. Removed the hotmelt to the ps h/s and desoldered/resoldered
with a lean so more of a gap from the h/s
The PA is grounded to chassis , but not the PREA, umbilical ribbon
connection only, input is plastic with no grounding ring.
With all the guts of the amp removed from the case then touching the Master
vol pot stem induces a lot of hum. There is no scraping away of paint on the
case for this pot , so could be making and breaking contact .
Needless to say have not been able
to induce any noise like this.
Further info from the owner
" It's whenever there isn't a signal that the buzz persists. I first noticed
it when i stopped playing in the middle if a song and i heard this murmur"
140K MP3 , 5 second file, is (theoretically ) now on/off this host site
http://www.diverse.4mg.com/amp_buzz.htm
(minimal htm page to get round "forbidden" remote linking stuff )
When I've a bit of time , will add a few more sound snippets to be able to
direct owners to
Any more to add to list of , simulated or actual , faults ?
"static" excessive amp hiss noise
howl-round / squeel
simple mains hum
mains buzz from failure of bridge rectifer
clipped signal
one polarity only of push-pull output
"motorboating" of open-looped amplifier
compression/ lack of compression
another one is the ting-ting noise introduced by an audio valve/tube with
C/H leakage and then highly susceptible to vibration, can be self-induced
via combo speaker vibration, giving those tings
I don't know how fidele this recording is, phone -> email -> MP3
player ->DSO
but I make that a principal repeat of 103 Hz and next most observable repeat
of 475 Hz.
So is it mains initiated ?
103<>100 , I will assume that is twice mains frequency as principal
component
With this amp and the Return Effects bypass switch to ground,
not noted whether serial or parallel mode. If it breaks
it does not kill the amp but is highly sussceptible to injecting hum into
the amp. There are 6 chances of a break in that line.
That switch
a simple .1 in space 2 of 3 pin jumper in series with it
4x IDC ribbon headers, on two ribbons, links to the PA
Although , as received , the headers and ribbons were made, there was very
little force required to separate them (as well as no glue across them). I
will go with opening of this line somewhere as the fault and something to do
with none of the PREA is directly grounded to chassis, with or withoud
Ground-Lift
Perhaps just replacing input and EFF-Ret socket and a set to these header
pins plus glue spots.
Will try a heavy throughput with amp in the chassis this afternoon , in case
a more electronic type fault.
I don't like the way its consistenetly half-hour in and no amount of kicking
or tugging will change the buxx once it starts/
It seems the ps h/s is heated by the internal air as it is near the fan,
rather than cooled, but presumably within allowable parameters, cannot see
any retrofit way around that.
So with the top removed and replaced with a large book, a thermometer over
the PA hs and another over the ps hs and one in the fan exhaust, ambient 20
deg C
All controls at mid and 4R dummy load
Initially 12.04V ac out for 6 minutes and then reduced to .1V input/ 400 Hz,
and 7.47V ac out,
reducing input to 1/10 while removing top and reading the thermometers for
that 30 seconds or so and loss of internal heat
6 minutes , 11.93 Vac, pa 72 deg C, ps 33 , exhaust not yet monitored
input reduced
15 m (6+9), 7.37V, 72, 45, 33 deg C
23m, 7.34, 72, 47, 36
30m , 7.33, 69,50,36
40m,7.32,77,52,37
50m,7.32,76,53,37
55m , 7.32,75,53,37
I reckon if the ps hs was not being heated by the internal air it would have
been only 35 to 40 deg C
No sound distortion emerging . So will just make those socket changes and
few paliatives like removing the paint on the chassis around the pot bushes
and resolder the usual suspects
I think I will try a baffle in this amp to keep the PA heat away from the
PREA and interboard headers etc . Those ribbons were surprisingly hot from
that high power test. Obviously if on repeating that high power test , the
PS h/s climbs excessively then my thinking is suspect and can easily revert
to as "designed". Incidently this amp , no load, SMPS runs at 380KHz , much
like the other Mark Bass that required serious work to a month or 2 back
I don't know what the extraction force should be , whether this is good or
bad.
Decided to pull out the PREA-PA 10 way ribbon IDC connector, when cold, one
took 550 grams , the other at least twice that. Going by how hot these
connectors got I would not be at all surprised one of the spring metal
contacts relaxed , either in this ribbon link with loss of a DC rail or the
front to back ribbon board carrying the EFF-RET
the weaker header conn was the one further into the heatflow from the PA
heatsinks
I think that fireproof card will stay in there. A long half-swastika one
along the front edge of the front PA H/S outside the vertical w/w
across the amp and to rear of the ps H/S
110+142+80 x 65mm cut down a bit to cross the pcb and a tapered top to
leave a gap over the ps h/s for a path to the fan, B/W wires taken inside th e80V
caps and hotmelted to the mains cap
and a smaller L-shaped one along the rear of the rear PA H/S
65x (40 +130)
. That
one removing the free path run straight to the fan, ie forcing air through
the h/s vanes.
The other one stopping short of the inlet grill to allow some unobstructed
cool air along the long run over the PREA and the ps to the fan
Todays results, adjusted down for an ambient today of 22 deg C, and starting
with similar 7.5 V ac over 4 ohm
5min , PA temp 64, PS temp 26 , exhaust 25 deg C
13 min, 74, 37, 35
fan running noticeably faster by now
20m, 74, 40, 37
30m , 74, 42,37
40m , 74, 44, 38
50m , 74, 45, 38
considering the stem of the ps hs thermometer I had to make a hole in the
card and the end of the stem was then in hotter air than the bulb end temp
maybe. The interboard connectors etc were noticeably not so hot. Makes
thermal runaway to destruction of the SMPS less likely if the amp is driven
excessively hard, hopefully. As far as I can tell with these amps , thermal
monitoring is only on the PA heatsink , not the ps one
yesterdays figures
15 m , 72, 45, 33 deg C
23m, 72, 47, 36
30m , 69,50,36
40m,77,52,37
50m,76,53,37
55m , 75,53,37
2 csk screw in front facia to remove
NE556 over-I and over-T
R84 47R, R74 K
1W 270K & 470K
7815 & 7812 tabs to h/s
Sp at jack 5.2R
Resoldered all caps and Qs
2.5mm bolts and nuts hotmelted in place as "caged nuts" on replacement XLR input
Returned a year kater with bad input socket ,Mark Bass Little Mark 2 amp (Italy) use no-name 0.25 inch input sockets (4 numeral molded
underneath and 3 pin holes each side of the body) . Eyeletted before
soldering but after desoldering with fresh solder, to aid pressed/eyeletted
removal , 2 of the pins have no wetting and dull finish other than solder on
the cut ends. One pin active , other pin just physical holding ,not
electrical, but eventually intermittant contact of the active one.
Are they just slid over the pins , relying on friction while
handling/placement and then at soldering it is assumed solder will get
between the lead and eyelet as well as between eyelet and pcb pad ?
I've never been in production but its easier to align eyelets singly onto
pins of an IC or in this case socket than try to align all 16 pins of an IC
into pin sized holes in eyelets already in an array in a pcb. IC socket pins
, turned or sprung, have location wells to assist this, but eyelets don't
Release 6 sc for amp and ps but keep others in place because of the card
baffle added before.
Slide out of the way to remove prea. Wire in the a replacement socket , bend in one
tag to clear the XLR. No name i/p socket , mould mark 4 underneath
Mark Bass Minimark , 2008 PbF
Owner only used the line out to house PA, with sp off , but crackle problems on that line
but switching to internal sp no problem it would seem, and touching the conn would
affect it.
6 large sc at rear to release amp, at least good fan air path in this Mark amp.
sp 5.4R
As usual SMPS IC ground off
+/-54V main rails
odd pins on umbilical (evens are gnd)
.7V,15V,-15V, 0, n/c
mid controls .1V 400Hz in , mid controls, .045V ac on p7
, 16mV on line out
if orange wire connection to sp sw is disconnected then sp off
p7 via R29 100R and R50 220R to p1 of the optoH11AA1
Alternate sets on all header pins and then tried engraver and nylon bolt
while monitoring line out with a test amp and phones to block engraver noise.
C9,C11,C12 and C8 resoldered as microphonic . Engraver bashing didn't show
up anything else. Ratling those C did not affect headphone op
250W amp - Parsek Mark Bass , Little Mark 250, of 2008, Italy
Mains fuse blew in the middle of normal use.
No mention of PbF anywhere but it is. Unlikely the problem though. Seems bad
thermal design as audio-out vaned heatsink has cooling air through it but
the non-vaned SMPS one does not have, as that intended? air will go through
the path of least resistance over the uncluttered preamp . I can see a
baffle going in here to direct air over this plain block heatsink. Anyone
experience of these little amps?
Both SMPS powerFETs s/c all round. Each has a discoloured patch on the
mounting-plate where the die overlies. No burning/blow-holes of these
powerFET encapsulations or 10R SMD gate droppers or anything else found
suspect from cold testing/close inspection, nor suspect looking PbF. The
SMPS supervisor IC ident is ground off and a schematic for a similar amp
has no ident. I could find details of any 8 pin 0.1 inch pitch package with
push/pull drive in 1991 DATA linear colated listing- any suggestions for
this sort of search?
p1 supply low side
p3 probably Enable
p4 Vcc
p5 and p7 hi/lo outputs
p6 mid connection to both output powerFET
Does not seem to be any thermal shutdown for the SMPS section
From digeykey filter search , these are 8 pin SMPS ICs , now to see if dual
drive
LTC1041
NJM2103
TDA4605
FAN7680
SG6203
Will jury-rig with a couple of IRF740 in there at 70 percent mains to check
if the supervisor is working.
Can "totem pole" types be used as dual drive? A TDA8130 would go in there
pinning-wise, with 6 of the 8 pins rewired, no idea if correct operational
parameters though. Before trying a pair of 20 amp/600V powerFETs.
Is there any point in roughing the surface of a flat shiney aluminium block
heatsink or painting black for better heat transfer, not really space to add
vanes to the block
The SG6203 in that list is totem-pole but the source/sink split is not
available at the output unlike the TDA8130, so none suitable from that
sub-set.
I checked the pcb traces and pins 1 and 4 are swapped over on that schematic
, the 270K dropper agrees but ground and supply are swapped so pinning
agreement with those IR... ones
Zeroed in on IR2153
different powerFET pair but overlay device numbers/types etc correcpond in
the SMPS area otherwise
http://www.eserviceinfo.com/download.php?fileid=51892
Different heatsink types and different layout to the pics shown in that pdf
Would you trust amp repair to a company where they pull knobs away with
carpenter's pliers?
I assume that is the reason for the ground off ident, to lock into their
repair shop
With 2x IRF740 in there and 60 percent mains there is high current draw,
some smps type oscillator start up noise and mains draw current drops right
back with 180V over the main bridge rect , switch off and that 180V takes a
long time dropping to 150V with some low level audible osc type noise . No
led or fan tries turning , perhaps needs more than 60 percent for this or
something else wrong, will have to try monitoring SMPS output before
venturing higher
I will try a 72V zener over one of the Brown-out?
zener chain of 220/200V zeners, while srill trying with 60 percent mains (2
x200V caps across the main DC - reminder to myself to find a workaday
formula for "Vz" of zeners at 1/10 to 1/10000 of rated current )
That 470K must put the current into the uA regime
I doubt the Ebers-Moll sort of stuff applies in this sort of illegitimate
area of operation.
Tried a 6.2V 1W zener
Vz 6.22V (initially then rising) @ 78mA
96 percent of Vz @ 7.4mA
95% @ 810uA
92% @ 102uA
77% @ 9.6uA
66% @ 2.6uA (4.12V)
I'd forgotten to at least try the PA and its ok up to +/-25V dc on a bench
PS , 63V rated caps, so less than the 80V of that schematic.
The PA is certainly different to that schematic, pair of those 5 pin SAP
devices with intimate thermally connected sensing diodes
I thought startup was a bit quiet, somewhere along the way I've managed to
short G-S on the high side IRF740. The other one changes state on DVM
"diode" test. Shorted turns on the switch mode transformer ? Change C68,
perhaps punch through ?
A dropper will go in with changed 1uF and new sacrificial IRF740 tomorrow
1KHz RLC testing of the Tx
feedback coil .039mH
240V tap 2.37mH to gnd
230V tap 2.22mH
100V 1.8mH looks reasonable
Along the way that Zener3 in the 200+220V zener chain is probably 6.2V (at
low uA level) and the 2N7002 (SMD topcode mark 782 R) functions as it should
There is no jumper configuration
in that area for 100/120V countries so must be completely inoperative , in
mormal operation, in those countries
I've acquired a new IR2153 and desoldered the original unkown driver and as
the Tx primaries are some distance from the driver IC, soldered in a turned
pin socket. The old one has Thailand and R3 mould marks on the underside and
perhaps the second line on the top starts with a 7 and the third line ends
with a 5 . I'm assuming there was a top line that is well ground out.
Will power up with a couple of droppers in there with 60 percent mains ,
still set on 240V jumper.
I can now compare old and putative replacement
A bit further forward I suppose. Exactly the same, for 2153 and original,
audible low level oscillator noise , 10 seconds or so after switch off
presumably coming down from ultrasonic and dropping in pitch over a couple
of minutes while there is HV in the main caps. And +/-0.5V on the main rail
caps transfered across the Tx from the startup pulses, instead of the +/-60V
or so . But no sustained drive. Next is some monitor of the Tx primary
feedback route to the driver and somehow monitor the osc f, perhaps change
the SM cap is easier, the SMRs measure ok. Any tricks for fooling the driver
into thinking there is more feedback than actual, a battery wired-in?
I am getting very inconsistent poor to bad ESR with electroC69 so will
change that and C70.
The 2153 has Thailand in a dimple on the rear of the package and an empty
dimple on the diagonal, this structure the same as the ground off one, minus
the R 3 .
I wonder how many IR 8pin , that pinning packages , were available in 2008
and a year or two before. Unfortunately I don't like using isolation
transformers and scopes on SMPS to narrow down a bit more, if I regularly
dealt with SMPS failures then perhaps it would be different. If this one
wasn't a lot of difficult to probe SM around the DIP8 SMPS driiver ,hemmed
in by heatsinks and large caps then may have been different
So that 220/220V zener chain is perhaps more for the possibility of someone
jumpering JP1 to 100V and plugging in to 240V and instead of 350V dc trying
to get to 700V dc
I now see someone else has been here before and ground off IC5
music-electronics-forum.com/t10881/
What is the difference between IR2153 and IR21531?
The original has a diode between Vcc and VB so perhaps whether 2153 or 21531
or any other IR it should be the D variant or adding a high voltage diode
externally. Just checked again
The polarity pip of the original was not ground off and p1 is connected to
the dropper from the + of the HV dc caps , ie Vcc and p4 is connected to the
zero/negative of the HV caps (not ground of course) . So someone getting his
pin convention wrong I think, overlay "pip" is obscured by the chip and
agrees with the original orientation of the chip
I'll sling a 4007 under the board beefore powering up again. As my 2153
started pumping out some pulses and oscillated , at least in audible range
with low Vcc, then I can assume pins 1 and 4 are not as in that Mark Bass
schematic.
Something else I've noticed on SMPS generally before but not thought about
why. Around the elevated mains voltage area a line of slotted perforations
in the pcb material. This must be more expensive to produce than a hatched
wide line of white ink at the overlay stage. I cannot see ventilation or a
paliative to possible developement of conductive pcb material as being the
reason
Thinking back to the original failure mode. Solder joints all looked ok ,
but this is definitely PbF although absolutely no mention anywhere. The
holes in the pcb, for the powerfets , although plated through, are 3 times
the required diameter of the width of the powerFET pins and no eyelets
padding out. If bias to a gate failed then that could easily short circuit
that mosfet, would the other one fail soon after, if the amp is in use at
the time.
With the IR2153 and 1N4007 and 10R dropper (actually 24V 240W halogen lamps)
at hot
side of hottest mosFET and in line with the 1uF coupler to the tx and 57 percent of mains there is life
Blue power LED on, SMD LED D20 on, fan on, +/- 31.6V on main rails , 7.7V on
12V 7812, -9.6V on 9812 and 9.2V on 7814.
Then hot side , 12V on new 10uF C67 and 13.5V on new 100uF C69.
But a minute in and that 4007 smokes and mains current draw rises from
nothing readable on variac AC analogue meter to about .15 amp and I switch
off. 4007 survives as does the IRF740.
Is this a result of me trying to run on too low a HV dc and removing
droppers and taking mains to 75 percent or so will remove this or something
else wrong. I cannot believe that bootstrap diode would be more than 1 amp
inside a D suffix 2153 DIP8 package.
I have the fall-back option of refitting the original driver chip but think
I'll carry on with the replaceable 2153 for the moment, monitoring the
voltage on the R78 Vcc dropper , first I think, in htat first minute
Where can that power be coming from to heat the bootstrap diode? Not the Vcc
dropper , far too ohmic, the 4148 D40, 150mA or so is fine . I will
disconnect my added 1N4007 and see what happens to those main rail voltages
A bootstrap diode is required, without it and its back to no output and that
low level descending pitch audio at switch off
Must be passing too much HV ac , ie too much leakage. Tried 2x 1N4007 in
series and no problem over 2 minutes, and no heat to finger touch soon after
switch off. Enough time to put a sniffer coil next to the SMPS Tx and
stable operating f of 430 KHz.
For 330pF and 18K the IR2153 shows expected about 120KHz, influence of T24
or low Vcc perhaps, 11.5 and climbing above 11.6V at switch off
So do you need a high frequency , and high voltage diode, here if only a few
tens of mA of DC required to pass but need to block 100s of hf V ac in
reverse. Or just low leakage and high voltage silicon diode here?
From IR application notes it looks as though the internal bootstrap diode is
actually a gated powerFET in recent manifestations of that IR215. series.
The accepted external diode for a IR2153 seems to be MUR160 so placed a
BYV96E in there and it is comfortable. Removed the droppers
Raised supply to 66 percent mains and voltages coming up to +/- 36V,
presumably between 50 and 55 V main rails with 100 percent (this amp is 250W
rated, that schematic is 500W)
Same oscillator frequency
Time has come to replace the IRF740s with pair of 20 amp /600V powerFETs
Split down the middle a TO3 heatsink with 2 lines of vanes, bolted both to the top
of the existing Al block PowerFET h/s
3 white SMD diodes D16,D?, D20
Had it running under load, osc f 380 KHz, taking temp readings of both
heatsinks until stabilised without fan cooling, top cover removed , but
monitoring the fan DC .
Can mosfets go ohmic with age as I cannot see that ps heatsink getting all
that hot. Did a single powerFET going D-S randomly short then drive too much
power into those 2 caps to make them fail and knock out the second FET?
Could there be a flaw around the design that with bad ESR caps , instead of
going into protect mode could the driver IC go into a fast cycling
restart/protect mode and somehow overdrive the powerFETs to knock them out.
Both shorted original powerFETs had a discoloured area on thge heatsink face
as though overheating,
Infuriating having so few clues, and having to conjecture failure
mechanisms. Shorted mains fuse from 2 D-S shorted powerFETs and 2 bad caps
and no other obvious overheated Rs etc
Used SMD D2PAK STB20NM60 modified to fit TOP3
low mains
+/-29.8V
7.4V,-7.9V,8.9V
159V mains, 2.6 uS osc period
+/-36.2V
9.4V,-11.9V, 10.9
relay clicks over after 2 sec
200V, 80 percent mains, no load
+/-46V, 11.9V,-15.3V,14.4V
and IR2153 Vcc of 11.8V
100 percent mains, no load
+/-53V
8R load added, i/p voltage not noted, 10V ac over 8R, no cover over amp
so fan ineffective
osc 2.6uS/ 380 KHz
Thermometer over mosfet h/s reached 7 degrees over ambient
and switched off as SAF H/s too hot to keep fingers on, fan speeding up
Coled down
all controls mid, 400 Hz, .11V (maybe 0.011V in )
O/p over 8R V taken,Fan voltage, mosfet and SAF h's temp and times noted
SAF temp stabilised after 20 minutes with amp cover removed
O/p dropped from 6.38V ac to 6.34V
Fan up from cold 5.9V to 11.6V
Mosfet H/s rose 7 deg C
SAF h/s rose 33 deg C
ps
Got word back on this and its survived a number of gigs including one where it was pushed hard.
So a pair of footprint-converted SMD STB20NM60 and that IR smps driver + diode are an adequate replacement.
Thinking back about it the owner reckons it may have been a song sheet sloppily laid next to the air inlet was its downfall.
Marshall limpet knobs
Seized on ones as used on combination pot and switch so grub screw
anchored. With luck the grub is screwed into plastic and not
a captive nut. Wrap some plumbers PTFE around the tip of a soldering
iron and apply for 20 seconds before attempting to unscrew. Maybe
softens enough to release knob by turning. If when removed and further
10 seconds of heat does not turn, then heat further and push the grub into the
core. Retap for a larger grub.
Marshall 1987X from 2006 and probably other recent models.
Traditional chassis mounted pots ie with loose wiring, not loomed, not pcb
mount ones.
To save cutting small holes in the front fascia, to take the pot
ant-rotation lugs, they've cut them off and then not even secured the pots
with star washers under the bush nuts or fascia. So even in careful useage
the nuts work loose in a couple of years which is fine inside an electric
quitar , just a rat's nest of knotted signal wires, no elf 'n safety issue
there. But not for valve amps - needs a modification to stop each of the
pots rotating and then bare connections touching.
The 1mm tinned copper wire earth strap soldered to and across each pot is
not enough to stop, wire breaking and the pots rotating.
If in an electric guitar I replace the wire with flat copper strip, soldered
to each pot case, the sort of enamelled high current wire used in some power
transformers, with the enamelling stripped off.
In these sorts of cases, not wishing to add to any electrical hazard, 1/8
plastic rod , bridging the back of each pot,
and then paired 1/8 inch cable ties around each pot and the rod.
Make sure the tie is lodged overe the aluminium fixing
points and not the paxolin.
These amps have a printed plastic finnish covering over the fascia metal.
With a thread lock chemical approach the plastic can still compress under
the bush nuts ,microscopically, plus metal creep and soon the pots will
turn if the knob is rotated to either endstop.
The anti-rotation lugs are there for chassis mount ring tagged and wired
pots precisely to stop any chance of rotation - up until the point is
reached when the the pot has fallen off , that is.
If the wiring was loomed and laced tight it would be a reasonably
satisfactory alternative .
"Repair" job, that awkward type of one where no fault found.
I can understand lager chillers or lighting triacs causing clicks and bangs
and noises off but blowing fuses on 2 Marshall valve amps at the same time
and no other pub mains problem showing itself.
This 1987X kept blowing 500mA HT fuses after the
initial failure. Not doing so now its in front of me. Mains fuse always
ok , just the HT one repeatedly failing after 4
seconds or so. At the same time as this HT one failed the mains fuse failed
on another Marshall connected to the same supply - that one just required a
change of mains fuse and is still ok.
Could a fault causing failure of HT fuse on one amp cause the failure of
mains fuse on another amp , with no pub wiring problem at all, even problem
local to the power ring/spur to the stage.
Owner didn't notice anything else wrong in the room at the gig and
confronting the landlord he said he'd had no problems.
Checked the valves and transformers , caps etc and everything seems hunky
dory , no wavering of HT of about 440V on dummy load. I looks as though it
will have to be replacement 500V, twin 50uF electrolytics although no
suspicious heating or bulges /weeping, unless an indisputable reason can be
found. Fuses blew to black interior, ie not soft blown.
SS diodes in this one.
Amp is in pristine condition and owner never goes above 3 .
5 off 500mA (T) fuses blew black before but no problem while here
According to Regulation 27 of ESQC Regs 2002, UK mains should be
230V +10% - 6%, which gives a range of 216V to 253V.
I variaced up to 250V , switching on and off a few times, giving HT1 of 464
, nicely stable with amp under load.
A thorough inspection of all components only revealed slightly loose nuts
holding the iron laminations on the filter choke, which I cannot see as a
problem. Otherwise inside and out it looks brand new, only some of the large
binding post (lead-free of course everywhere ) solder joints looked grey but
otherwise sound.
On the assumption that the one of the 2x 22nF, 400V DC decouplers to the o/p
valves could have failed and self-healed, I replaced those.
Marshall 2266
Intermittant buzz then all the time with all controls at min, take vol/master to max and the buzz reduces.
Reduce mains by varaic and the frrequency of buzz pulses reduces, mains amperage fluctuates in sympathy
with the buzz. White or blue ch.
Disconnect conn 9 and in blue, stays same
Same with conn8 and conn `2, conn5 and conn7
Problem inside a KT66.
On testing C.H/R and C/H near enough 0
VLVE00039, WK25/08
DVM resistance and pins 7-8 measure 0 , but changing orientation and you can make it vary all the way to above 30M
but no noises heard from anything loose inside
Marshall 2555, JCM25/50, Silver Jubilee 1988
Gain fades right down after an hour and sometimes intermittant drops
Mains Tx primary 13R
o/p primary 14.3/15.7R to HT fuse
pin1,V1 metal spring of valve base gone soft so breaks
contact to first amp aode after an hour of warming and bad solder to wiper of first switch+pot
giving the intermittant, mainly
Another bad solder joint and a number showing part circle impending failures,
not just the pots but those probably helped along by poor
posistioning/locking of bush back nuts. Requires 3 nuts or deep collar and
front nut for integrity.
Marshall 3310
low output in clean ch
All mid pots
55mV 400Hz in , 1.6V out in boost
.13V out in clan mode
with all 3 volumes at max , same input .9V out
Tank bk 32E, R 197R
Tx 9.1R//.9R
2x .33R resistors
Owner had used too much switch cleaner for "scratchy" pots , built into
insulation under wiper of VR5. With needle probe , so insulated handle touching VR5 wiper
terminal injected a lot of sinal into the output
Bypass on both send and receive so
10mV 400 Hz in all mid pots , no reverb connected
.48V boost ch and 1.14 V clean (log pots)
JCM800 , 4210 STD, 1986
poor controls clean ch ok but boost low level and poor
Celestion 16 ohm, measured 12.2R, G12M-70
Tank Accutronic 4DB3C1D R 202R, Bk 33.1R
Most pots bad, twisted pins before soldering so force out through pcb , loose rivets on some
needed squashing and wipers moving. Double pot renovation see tips files
Tank Tx 287R, 3.4K
Mains Tx 9.8//78R HT
uses 3046 , note overlay "IC1" not at pin 1/p14 end, replaced with turned pin socket and new one to cure boost ch problem
but may have been bad solder at boost vol pot or C9 soldering
TR2 , BC184 , to reverb pot and 1K to footsw
TR1, BC184 to LED
4100/JCM 900
This on a 4100/JCM 900 but presumably found on other wide cab valve amps.
Front panel replaced with translucent smoked brown plexi-glass and Marxhall
white 3D
logo over it, reflective "silver" lining to the rear panel and running
without screens or
retainers on the valves , for visible effect. But heavyish plexiglass sheet
only relying on a few glue spots onto the rexine covering, itself glued to
not much woodwork. So nothing much holding it in place, now a few glue spots
have failed . Any ideas on how to make a firmer fixing without drilling
holes through the material. There is white trim around top and sides of the
plexiglass , bonded to it, that could perhaps hide fittings
The owner was aware of it being loose (1.2Kg) and he is going to sort it out
by gluing back, apparently he's done it before, so not my pidgeon.
He reported that over time whereas he was comfortable with 1/3 vol clean ch
setting , he reckons that imperseptibly over years he now needs 1/2 vol
setting.
3x ECC83 , generic recommended gain 1.6
these measure
v1 / 1.3,1.4
v2/ 1.0,1.2
v3/ 1.2,1.1
av 1.2 over 6 triodes would
account for that gain drop?
4x EL34 all fine at 13 to 14 at 59 to 66mA
Whatever the glue is , it is fine on the plexiglass. What has failed is the
surface , only, of the rexine has sheared off. So perhaps baring back to the
underlying wood is all that is needed. On the other hand there is a
noticeable bowing in the plexiglass , perhaps 1/4 inch over the length,
presumably due to heat, helping to shear any bonds on the sides
reverb 33R/198R
tr 4.6R// 13.9R w/p, 0.68R r/bk
prea pcb retainig screws need lacquering
spacers on 1/4 in so
loose IEC bolts
Marshall 4140 valve amp, 1975
Been in a shed for years and no known history so treading cautiously.
Measuring the DC resistance of each side to centre tap of this Marshall amp,
shows only about 15 ohm each way for o/p matcher.
Amp is 100W o/p using 4 EL34 , two paralleled anodes going to each side of this impedance matcher.
Output resistance of about 2.5 and 4.5 for 4 and 8 ohm settings seems fine.
I put a 1KHz AC LCR meter on the coils and it comes out to 32 Henries for
each half.
Amp is 1975 , from electrolytics, and uses Si rectifiers,
choke is (in circuit) 105 ohms DC.
Charred/burnt 1.5K grid resistors and blown HT fuses.
All valves ( all marked Marshall) checked out good on Avo CT160 - I'd
forgotten how problematic , with high current valves, to get the initial
zero on the meter before rotating the SET mA/V.
I always power up kit left idle for a long term with a variac + current
meter + thermal trip.
Perceived wisdom in such circumstances to power up valve amps
with full speaker load on output with all valves in place and to power up
transistor amps intitially without load.
On the slow variac power up, I usually power up to about 80 per cent mains
with no valves in and then add the valves and then go low to 100 percent
Replaced the burnt stuff and its back working.
Unfortunately after about 10 minutes hum makes an appearance and after half
an hour becomes excessive.
I stuck a piece of 20 to 35 degree C thermochromic paper to each of the 4
can electrolytics and one is heating up.
Its normal for each of the 4 EL34 to have a blue glow observable
through some of the holes in the internal metal-work as well as normal
orange heater glow.
Replaced that dual cap and runs cool and no hum after 10 minutes.
But after an hour a hum develops, intrusive but not as bad as before and at
the same time a serious glow forms on the zinc coloured metalwork of one
pair of the EL34s.
All 4 EL34s tested good , otherwise just 2 off 1.5K resistors to the grids
of each EL34, correct values cold.
The push and the pull from the preamp are AC coupled,
replaced all 4 22nF, 400V caps in that area.
Not a problem with the DC blocking caps at final push-pull separator stage.
Replaced and still hum after 3/4 hour.
No DC on the ganged volume pots.
Monitoring the negative bias for the output EL34s.
10 minutes in, the -ps voltage at smoothing cap is -52V.
The voltage to the (schematic marked) B pair is -39.2V before going to 1.5K
then g1 of each EL34
For C pair -39.2V also
25 minutes in B = -37.8, C=-34
45 minutes in B= -36.9 , C=-32.5
hum is getting quite noticable and -ps rail is still -52
Increasing bias pot from its original of 8K to max of 22K
brings the -ps down to -53.5
now B=-39 and C=-33 less hum but still going more positive over time and hum
increasing.
I stopped before the B pair started glowing like before.
I was expecting from these voltage readings that it would be the C pair that
would start complaining.
Switching off the amp, not just to standby, for a couple of minutes ,
brought things back to original cold situation and another 3/4 hour
presumably before hum gets too much.
One thing that concerns me is each of these 1.5K g1 resistors has one end to
the valve base pin and the other floating in space , not soldered to an
insulated pin just the wire connecting through
Tip from "Arfa Daily"
"However, before rushing out and buying new ones, you can
start by removing both the C valves ( these are the ones that glow
ultimately - yes ? ), then removing one of the ( likely ) OK B valves and
putting it in the C side. The amp will run quite happily with just one valve
in each side ( it's a trick that I teach owners to allow them to finish a
gig if they have a serious valve failure ).
You will then be running it with two valves that have performed OK when they
were both in the B side, so if it now works ok, next put them into the two
unoccupied sockets instead. If it still continues to work ok, then the
chances are that it is a valve problem. If it doesn't, then it must be a
bias issue. This assumes of course, that it's nothing to do with the output
tranny, which could suffer a partial insulation breakdown, resulting in
shorted turns, when it has been running a while. Again, this could be
checked by swapping the winding ends betwen anode pairs, and seeing if the
bad behaviour swaps sides."
Swapped pairs of valves with much less hum noise and
better sustained negative bias
but assumed a new set of valves would be the answer or
having to switch off for a couple of minutes each hour of use.
Marshall 5210, 1988
left in a shed for years
50W Tx 30.6// .9R
speaker Celestion G12 M-70 , 2R9
4x .33R between H/s
270R headphone
2x NJ2501, 2x MJ3001
2x 072, 2 x MC1458
Pot shafts seized up as corroded, removed and rubber collar placed over bush and oven cleaner over night.
Pins of pots are bent over before soldering so matter of graunching through the pcb with a 5mm
flat screwdriver under the elbow of an outer pin while desoldering it and centre one.
Pots Alpha Taiwan
B22K x 2, A1M, B22K, B220K, A1M, B22K, A1M, B220K, B22K
Tank R 189R, Bk 30.5R
Needs ground screw on pcb for testing.
Bad return bypass sw and bad footsw socket sw as would power up in Boost ch , not clean.
Replaced those and input socket.
Without reverb tank, keep its control off as will lead to distortion.
All controls mid, clean ch, 400 Hz , .1V in , 2.4V ac over 8R.
Pu
Pk
Bn, R
Y, Gnd, Br wire colours along rear sockets
Marshall 6101, 1992 combo, 29Kg
Crackles and bangs except at low volume
and tinging output with fingernail scraping across
the turned metal covers of the knobs..
How to remove the digital board to get to the valve bases hidden under it.
The Switchcraft XLR socket is introduced from the outside and soldered to
the board with the track side of the board inaccessible.
A cunning latch in the XLR socket that releases the internal part that is
soldered separatable from the XLR housing. With a
jeweller's screwdriver turn the slot at the end
of the socket housing to release the latch.
No need to undo the 2 mounting screws.
Shame about the "dp" pots used as they were well soldered in ,
double sided, requiring "soldering" first before desoldering.
Poor swage contacts between pot tracks and pins.
Removed and squashed in with parallel jaw pliers, treating all
vol and gain pots but perhaps should treat all of them.
5.6K 5881 grid resistors were charred but functional as was large
10K on preamp board , replaced with same wattage replacements.
As were the 47Rs in the +/-15V ps but replaced with 1W.
So problems on all boards. Remove the exposed screw heads to
release the boards , hopefully leaving the nylon parts
held by the nylock nuts. One ECC83, second from non-transformer
end replaced as C/H leakage of
4M, giving tinging. Number 4 was also on way out at 10M.
Punched out 5mm diameter bits of cycle inner-tube rubber with
a paper punch to pack out the each knob spline recess
to raise away from the fascia plate.
Speaker 5.4 ohm DC
All LEDs lit - release the speaker/line switch
No output - use outlet nearest mains inlet.
The earth point at the XLR is required for normal function.
No ch1 if conn1 lead is disconnected
Dummy load test, set for 4 ohm, 2.5V ac 400 Hz cont. sine in load.
Ali plate 3.25x7.25 ins resting over 2 large O rings
on the 4 6L6 and thermometer on that. Temp stabilised at plus 46 deg C
after 25 minutes.
Cutting HT then drops to plus 15 deg C, over, on heaters only.
Marshall 6101, loss of valve filaments and funtion.
Made in China 6L6GC have getter around base section of glass, not the top
CN418 1/4 spade discoloured red to partly black. Scraping back still showed black, not red.
Also the heatshrink had shrunk more than its fellows but otherwise no
signs of arcing or smoke until cutting away the red, crimping seemed fine , prabably
had welded itself, but replaced with a soldered blade
op tr Y-Br <>.1R, W-Bn 16.3R, W-? 16.1R
mains tr 4.9R// W-W 7.9R, W-Br 14.3R, R-Gn 9.9R
To reassemble use a 16mm spacer between chassis and cab to get mounting screw alignment
In for a problem in heater wiring, corrected and working fine on the bench.
Reassemble in cab and no output now. I'm loathe to have to now take the main
board apart unnecessarily if I'm doing somrthing silly as there are a number
of awkward quirks about this model.
Feed signal in the "Return" and it outputs to the speaker. Normal signal to
the front input and output at "Send". There is 0R across all 4 un-inserted
"return" socket contacts as per schematic. ch select switches and status
LEDs work but pressing the muting switch does not mean the 3 LEDs come on
together now as a reminder indicator (this function not mentioned in the
user handbook). I've removed the digital board and nothing seems amiss with
that (secret lock within the XLR). Relay click at initialisation at power
up.
Something awry with the series/parallel sw. I noted the 3 LED on, if mute
on, function with another 6101 but it is not the case here, makes perfect
sense in the absence of a mute lamp on the front, anyone any knowledge? This
one wrong or the other one wrong or just variants? or does it require jacks
in place or something as well
I'm wondering if the 3 LED lit thing is only at power up, I remember from
the other one it also locks out ch selection and maybe use at all via the
front input until de-muted.
Amp not open at the moment, looking at schema if SW301 is the mute switch
then no logic connection to the 8031A / LEDs. The ch sw lines go through the
8031A to the HC574 to the LEDs so I suspect electro C301 of the p9 reset for
random power-up problems
Marshall 6101LM, 1998
Smoke billowing out of the line in and out sockets
between sound check and use proper, so set in stasndby so
low mains current. All fuses fine. But 5A plug fuse replaced with 3A, 2A T
in rear chasis housing and 5A Q internal. Line cord replaced
as not only burnt hole but melted IEC socket partially
and heat transfered to the line cord plug which had part melted also.
Flexing of pins from the IEC socket over 10 years of
insertion/removal of line cord had broken the solder joints
at the pcb, but not the ground pin which is 0.5 inch longer.
Maybe compounded by mounting screws being too small a gauge
and brass (to match facia).
half inch radius burnt hole in the pcb so only the glass matt
remained in place.
Cut away burnt, cleaned off smoke staining all over chassis panels, and
wired in replacement IEC socket so mechanically decoupled
from the pcb, but surround re-rivetted to the pcb.
Presumably if HT was on at the time and arcing
at the bad solder then a fusing action may have occured before
heat build up could take place.
Also added high temp insulation sheet between transformer and
the ps pcb as close.
Speaker 6.2R
Relays click over at about 60 percent mains
Mains Tr 4.7R//14.1R, 0.1R
o/p tr 15.8,15.5?? 0.2R,0.1R set to 8 ohm , no speaker
If channel change+ LEDs fail to respond , switch off at mains and on
White connector -15V,15V, 23V
over 10K , R58 313V,445V
at pa black wire 227V, 6L6 480V
There was also bad solder on a heater wire from one of the fuses,
so only mechanically connected.
Marshall 8040 Valvestate V40, 1993
Intolerable hum/buzz, with or without the valve.
100 Hz amplitude modulating the test tone and beats if tone is 100 x N.
And if close to beats f then interesting "Jacobs ladder" noise of slow rising and fast
drop in buzz f
Bad first gain pot and bad PA-In bypass sw.
Unbalanced DC rails , % of mains not noted
+10.7V , -13.1V for op amps
14.8, -22V for the TDA1514A
Preamp out signal is ok
Mains Tx 40R/W-W .6R
Tank in cct 198 , 32.4R
Discharge pin1 of the valve base before removing the pcb.
Replaced both main rail caps , with higher ratigs, as one had totally failed to o/c.
Required removing the block-type polyester caps and fitting one over the other as
the replacement electros were wider.
If the input side ground wire is broken then excessive mains hum
Marshall 8040, 1992
valvestate 40V
bad pots from being in a loft for years, lubricant gummed up the
tracks. Speaker 3.1R Celestion G12L
Run a steel rule between top of chassis and cab top to free
stuck mounts.
TDA1514A, ECC83
100R,2x180R, 2x68R
.1R, 10R next to it
reverb 32/202R in cct
spacers on 1/4 in so
Marshall 8100, 100V, 1994
No reverb, broken coil, 7.2m of 0.07mm wire, 31R and 200R
for the other one. o/p coil is grounded only.
Decided to slightly bend the brass retaining bracket
to release the iron lamina but difficult sliding
back in (very soft and thin iron) so drilling out
rivets is probably best.
Solder the tails to the phono sockets
with hotmelt linking the sleeving to the tags for strength.
Mains transformer 17.5R, .4R, .4R
HT transf 5.6K, 21.5R
Output T64,T65 darlingtons are 1.7V & 1.2V
diode checks.
Marshall 9200 (9100 on fascia), 1995
Bad output sp so , waggling jack affects it.
Make a hole in the centre of the underlying insulation sheet to introduce a hook to pull
outwards then a ruler along the side to lever out the sheet.
bush nuts 2R,2R,2W , 4Bk
Disconnected nylon pillars on 8x400V cap board to move enough to remove the
output board. Beware of the fibre washers falling off
Soldering seemed ok but the impedance sw seemed dodgey with a meter across it.
Twisted outer pins before soldering so a slog to desolder
Mark subparts before dismantling
Make C7K 121 USA V-series again. Cleaned out all the grease and reassembled dry
as the sw is never changed. Did both ch sw while at it
A plectrum either side then a dart point to flip the nibs , to release
Only .5mm clearance between 2 of th e20mm fuse holders so added paxolin between
both pairs.
2 x ECC81 valves unusually
Check the rear pcb tracks for breaks from brutish sw desoldering
nail varnish on fibre washers over the 1/4in so, before reassembly to avoid them
dropping off. Don't forget to reconnect the fan
One green LED needed resoldering
Mains Tx hum one ch , perhaps not noticeable over fan noise, tightened the 4 bolts
Quick and dirty check with dummy load (no speaker) ea ch
strong 1KHz input to pickup on Xtal earpiece noticeable on all grids ECC and 6L6 ,
Marshall AS50R, 2001
low level , 1/10 normal reverb, not didtorted
Reverb tank 214/34R
Bad solder on minor ps rail droippers, bad phono socket soldfer also
horrible foam strip on rear colosure, pulled off and replaced by 4 small rubber bumpons
Owner thought connecting phantom powered mic lead into DI socket caused problem ,
coincidence. But checksd, 2x2K2 and 22uF caps to p2 and p3 of IC1, 072
Marshall AS50R, 2003
Very low level of output
TX 33R//.8,.8R
speakers 2.7R
-31V, 29V supplies to +/-regs
+/- 35V power rails
With controls mid position 0.1V ac, 400Hz in an aux i/p
0.015V at line out
at conn 2 pin 1 .065V and pin 3 .049V
Putting 0.01V on pin 9 of the LM3886T
gave .44V over 8R
Only 5 years old and the Alps 20K lin master vol pot
had failed, either a build up of something
insulating on the resistive wiper or one finger of the conductive
wiper moved to inside the track and the other outside.
Marshall , AS50R, 2003 (earliest date, so far, for Marshall PbF)
Just found 4 PbF faults , no mention of RoHS/PbF on the pcb
as pre-2006. Distortion after an hour of normal use
Appearance probably but not definitively PbF, shallow cones rather than
domes but no pastey/crackle-finish or white blotchiness. Anyone have any
precise knowledge about their first using date?
Usual suspects, tie the 2 stand off Rs together with silicone rubber and
ceramic spacer, 1/4 inch socket pcb solder points . also the treble pot had
been knocked so rear nibs bend slightly
Replace the 2 plastic 1/4 so spacers with fibre washers
Marshall AS100D, of 2008
No output unless in echo effects mode. Owner put away for 2 years. Covered
in PbF & Rohs stickers.
Now I find no problem . Send/Return/footsw sockets are not active bypass
configuration. Anti-feedback on/off switch is iffy but I doubt would kill
throughput .
Any known URL for a schematic out there?
Then how to reassemble the 4-off speaker wire routing, rod fed thru pcb hole
and chassis hole and load a speaker crimp connector on the end of the rod to
pull back through, crossing fingers that it will not dislodge? I'm not
skilled in chopstick use.
The mute lines of the 2x LM3886 pin 8 go to the ps, so only sw on/off muting.
no analogue sw ICs
Now the 3 sections of the amp are out of the chassis on the bench, to
explore the FX on/off line and the horrible white PbF solder "joints". The
designed-as skew-whiff digital FX board looks my sort of bodged
professionalism
A straight rod cannot pass through both pcb hole and chassis hole, so
probably chamfer off the edges of the crudely made pcb holes and then 4
pre-laid cords/wires to twist/temp fix through and to the sp wire crimps for
final re-assembly
As the FX board is only held on by 1 nylon screw on the other side from the
header , so eminently loosable, I tried running with the pcb removed , but
normal amp action , sans-FX with FX sw in either position
if the mixed 1 and 2 signal fails to get to the output amps then there is a
second route via the effects board, but that route is fixed , ie no header
connectors , switches or pot wipers, leaving dodgy pbf.
I cannot see how failing switches for the anti-feedback notch filters could
pulldown the ch1+ch2 mixer opamp.
Probably resolder all in that area
Textbook logical fault-finding , shame PbF is not logical. If I make a
leaded component / wire link mechanical tester, anyone know what force you
should be able to apply without the lead pulling through the solder.
(for "leaded component " read components with wire leads, not components with
lead/tin solder)
I use thin nose pliers and some undefined , but attempted consistency, amount of
finger applied force at the moment.
Wire link failed this pull test on one end and now that end is pulled
through the PbF, the other end rotates in its "joint" .
So mixed ch1 +ch2 from IC201p1 to the FX switch and FX board , including a
wire link, is ok (for now) and this failing link from there on towards yhe
other end of the pcb and the 68K/68K split out to the routes to the 2
output amps. So with failed link, signal through the FX board only
Only another 100 or more of these wire links in this amp .
To release front grille , slacken bolts for amp to slide back and grip top of frame
and pull off the velcro.
Pull speaker wires from cab gives only just enough room to undo th espades and
joggle thru the pcb slots, made larger for reassembly, and also untwisted the wires
Sp 2.8R each
Will function without digital board in place. Remove to replace lower pcb
, then top one . Fit PA in place with 2 loose 1/4 in bush nuts , align the easy
nylon spacer then the 2 more difficult .
Lead 4 pieces of waxed lacing cord of thickness that will pass
through the terminal pin and tie off. Pass through cab and the 2 x pcb holes and
pull back through , tieing off temp. Pass an end through a few mm of sleeving
that will go through a terminal , tie to speaker wire and cover with and fair off
with upholstery tape and pull through.
Repeat for all 4 , leave strings in place put remove sllevings and interlock and cover
with cloth tape to avoid pulling back through the pcb holes as inadequate length.
I reassembled with the amp out the front of the cab, passed transversally though the top
to the back for final assembly. The wiring is biased towards the front, probably gives more room
to play with for wire pulling but for turning the amp to enter the cab is only just enough speaker
wire length.
Beware of wires catching in th eaxial slot of the protective gland.
Marshall AVT 50, 2001
drops in volume
replaced IC2 072bde with TI 072
R81 , 470R, upped to 0.6W
A number of bad solder points, icluding the
usual Marshall pillar rather than 1/4 inch spade connectors
120R 7W, 2x270, 0.22,270, 2R2
gain pot had been replaced with A100K
then B20k,a1m,b200k
a1m,a500k,a1m,a100k
b200k,b5k
Marshall AVT50 , 2007
No more than 2 years old and failed springing / closure of input socket
and because of leadfree solder all sockets had poor soldering that would have failed in a couple
more years and dropper Rs that would have failed sooner than that.
Transformer disconnected, 20R// 0.6,0.6R
2x270, .22, 10R 0.5W, 270 7W
HT monitor point on R44 nearest C17, 113V
+/- 34 "white" supply
-4V pin 5 of blue "ribbon"
CN4 0,-34V
LM317T on o/p board. Thermistor for controlling the 24V fan near but
not touching the heatsink. As very quiet fan, bent nearer the
heatsink and added white goo . No trace of any goo but slightly
puffy silipad under the hybrid o/p so probably overheating
as fan (13 V at switch on) was only responding to air/ bourd temperature
Marshall AVT100X,2004
input pcb colapsed inside from loss of bush nut
Replaced with new nut and a 2.2 inch long piece of hotmelt glue rod
fixed to socket barrel at one end and edge of main pcb at the other
Marshall AVT 150H, 2002
both tda7293 blown (neg to 0) due to o/p connected to
another amp o/p .
blown mains fuse
mains primary 6R, sec (Yellow) 1.3R, (blue) .8R
2x 2R2, 2x 68R (in circuit), 2x22K
.22, 2x 10R, 7805, NJM072, 4056, 2x 4011
one 68R solder joint soon to be iffy
+/-49V, +/-24V, +/-15V
24V fans, 145V at D112, ECC83 A1,A2 81V
Dummy load test with both fans disconnected and
aluminium "heatsink" unbolted from chassis and
thermometer laying on top with alongside the TDAs
3mm Al 270x 50mm plus about 270x100 mm under of the rest of the
folded sheet. 3V ac into 4R, 400Hz, 20 minutes to reach
stability of 45 deg C over ambient and drop to 2.95 V ac
Marshall AVT 275
Replacement and beefing up of input socket
Added filter cloth , glued into top vent, to stop any
small bits of wire, staples falling directly into the amp
The overdriven / bad bearing noise on the fans is usual for these.
Marshall AVT 275
No control of depth of digital effects, ADJ at maximum on one ch
Wiper of lower ADJ pot to red line and P1 of CON10.
4.2V on all that pot pins as 0 trace had a break.
Marshall AVT275, 2005
Wavering volume
Bad adj pot with mixer pot high and master pot
The front controls board is held to the chassis with standoffs held by push
fit ends into holes in the pcb. Then bush nut free pcb mounted pots and push
on knobs. Has anyone experienced the board dropping away inside. If the
limpet knobs work loose and then a bit of heavy handidness or knocking, the
pcb board will pop off.
Clouting knobless pots on this would guarantee the board dropping away
inside.
All that holds the board ,then, is 8 quartered pips into the 8 pcb holes ,
easy finger force to release .
Does make it a doddle to remove the pcb for repair, none of those awkwardly
placed triangular catch pieces or screws etc
this pcb not having been dislodged even
partially. I've never seen this approach used anywhere else. I could not
decide whether it was a neat idea or an accident waiting to happen. Just
measured one of these "anchors" , about 5 pounds to dislodge one stand off ,
so x8 for the whole 15 x 3 inch board, once the knobs were loosened/shifting
along the spindles.
2x 6.2R speakers
2x 10, 2x 22K, .22R 5W, .22R 10W
R213 & R201 68R in cct
7915CT (+ 7815 ? not seen)
2x TDA7293
Tx 5.8// .9,.7, (32V x 2, 18x2)
con 1 to con 3
1 scoop in , 2 bright out
mode sw as flats on mid posistion pots
con5 1.8,0,4.8,5,0,0,5,0,0,5
con7 5,0,0,5,5,0,0,5,0,0
con8 all 0
con9 0,4.2,0,2,4.2, 0,0,0,0,0
con next to C230 to op TDA
0,0,0,5.8,0,0,16.3,.5 with or without load
400Hz in .21V , 2.04V out over 8R
with mid pots, FX mix off, othe rsw off
400Hz .17V in , 4.7V over 8R
If no control on effects adj pot, on maximum, if all pot pins are at 4.2V dc or so
then the 0V line is disconnected somewhere.
Marshall AVT 2000, year 2005
Yanked guitar lead and weakened socket, replaced and
beefed up as per tips.
Removed the top plastic grill and glued in some
pan scourer filter cloth as I don't like
being able to see main power devices (staples etc ingress)
.22 10W, .22 5W, 2 x 10R, 2x 22K 1W,
R209, 211 4.7K
4x 3K3
speakers 6.4R
CCOP5, 7915,
primary 5.8R, secondaries 2x .3, 2x .5R
Marshal DSL JCM2000, 2005
clean ch ok, loss of distortion on other ch
Whether red or green channel , on rare occassions the output will go clean,
ie not distorted. Of course I cannot induce that at will. As the LED stays
on ok unlikely a sw problem, often seen with those yellow shaft push push
switches. An FET or relay contact problem ? but which one would be common to
both red and green channels? Valves all test out fine for gain and CH/R but
again which section would be common to red and green, a problem in the
splitter driver would increase distortion
Could well be that, Jalco white and black isolated sw 1/4 in sockets,
problems with those switches I've seen plenty of times before. I sent myself
on a bum steer with Sw1 and the wrong proxy probe points for the
inaccessible sw points, SW1 actions are ok.
Putting a pot over the open ch change footswitch socket then around 55 to 59
ohms you can get tone change with no change of LED and slightly different
resistance to dim LED and then a bit more change then both LED on situation
is just possible.
With very light touching of a rod in the enclosed Jalco Return socket ,of
the effects loop, I can easily get 2 or 3 ohms remaining on either of the
switches, 0.1 and 0.6ohm as found,so with amp heat that could easily upset
things but I've not worked out whether all or any of those 3 situations
could lead to the observed symptom of dirty channels becoming clean
Owner did not use footsw or S/R
Exploring the Jalco switches, the one nearest the send so. if non grounded
would only induce stray pick up from the Return opamp (assuming bare amp
with no use of S/R). The one furthest from the Send so. cleanly switches
Relay 3 with a transistion point of about 280 ohms. Despite being able to
get about 7Kohm by slightly pushing the switch, and holding there, all it
would do would mute the amp, not attenuate the throughput to the PA. I
cannot get an intermediary ohmage on the other switch above a few ohms
I don't know what I call my tool - engraver with nylon bolt in place of
steel point and bashing hell out of the pcb on max oomph, monitoring output via attenuated headphones
(because of the engraver din) , but looks as
though Relay 2 has a dodgey contact. Initial whanging finds approximate area
of pcb then turn down the oomph dial and bash components. Not had time to
check /substitute yet. But as in ultra gain area would make more sense than
footsw S/R area .
Also engraver susceptible IDC con 7, links 8,10.11 and R23 &R24
Replaced relay, soldered IDC , resoldered all else in that area
tank 210R red/ 25.8R black
V1 VLVE 00063 , V2,3,4 VLVE00055
Sharp points to the pins and easily bent metal.
To remove valve pcb 4 pk on EL34 and 6 long m/s on pcb
CON ? > CON ? numbering do not agree with the DSL or JCM 2000 schema that I have
push-push sw are .1 x .125 pitch , 2x6 pin 4p c/o
Marshall JCM2000
Marshall BS30 , 1995? Bass State
Intermittant cut out.
Leave back panel in place and remove amp.
Cloth tape over the front spire nuts , to keep in place when reassembling.
sp 3.6R
Compress and release strain relief and cut sp wires, make breakable
union .
Tx 48//.3/.3
TDA2050, 072
1R, .5W / 470K,4K7, 10, 680R
All bypass sw bad, replaced with wired-in upside down 4 replacements, i/p,send.ret, and
phones (switched ground)
Tank 2 sc at rear and the bag opens up
Marshal DSL50 (JCM 2000) 2002
Came in as suspect low channel A throughput as
compared to channel B, but this would seem to
be normal. Valves tested fine, no switch problems or
any other problems found. For equal output
the channel B knobs set about half the number setting
of channel A.
To release valve pcb only, unclip yellow wire,release 6 screws around
upper metalwork to release the long pcb standoff
screws. R23 270R soldering bad on rear pannel board ,
supplies the ICs rails with its fellow 270R
Marshall G50R CD,
Noise from the speaker ,in use, like normal mains switch off pop.
1A mains fuse , wire evaporated and black stain
Mole grip sto squash and pull out the sp lead clamp first using a large blade
screwdrivve rbetween gland shoulder and chassis.
Leave Tx end earth point, remove sc under, knobs and nuts and the pillar
at the Tx end, rear so, cable ties on the 4 mains wires and top of Tz
LM3886, sp 7.2R
-ve rail / AC1 short at the bridge rectifier, still there on cuttting the C65 ceramic cap lead.
Bridge marked
LT820 / PBC1003, presumably 100V, 3amp , replaced with 200V 5A
Tx 13.8R//0.6R (28-0-28V)
Marshall G50R CD , practise amp, 1999
Should be simple 1/4 inch so. S/R bypass sw. fixing, but for removing the
main board.
I ended up graunching off the speaker cable clamp as it is inserted from the
inside , not the outside and simple mole-grip compression job to remove it.
(note to myself, next time confronted with this situation, try a small
driver between black plastic retaining tongue and the hole in the steel and
push inwards on plastic bulk, may work but not tried)
A plain grommet will be going back there as wires are loop-through anchored
plus solder to the pcb only 1.5 inches away anyway.
How on earth did someone assemble as no clearance space, you cannot even see
that area as surrounded by transformer and heatsink and casing. Just
referring to the heatsink, made me realise they probably assemble board
without LM3886T h/s and that goes in last. But then I would expect a couple
of holes in the rear of the casing to facilitate screwing on , would need
some sort of miniature flexible shaft or right-angle-drive screwdriver to
tighten
Maybe the mains transformer goes in last, but very short wiring loom to it
and still you cannot see the speaker thru-hole area and awkward bent finger
tip insertion.
. I don't remember
coming across a situation of having to push one inwards to release, rather
than compressing with mole-grips and pulling from the outside.
As for installation tools , maybe useable as extraction tools but
doubtfully for the "blind" side extraction. No way they could be used at
manufacture of these Marshalls even with absent heatsink and transformer
,without a serious bend in the shanks and probably longer shanks to clear
the case metalwork
Someone has taken a pic
http://www.chambonino.com/routework/routewk12d.jpg
The speaker leads enter between number 2 and 3 white pillared W/W resistors,
calling number 1 at the foreground. The underside metalwork is 1/2 inch
below the pcb but somehow the strain relief clamp is inserted in that gap
surrounded by the h/s and Tx underside metal etc
And just to clarify. Before you can remove the pcb you have to remove the
speaker wire clamp as the wire has no slack between clamp and pcb loop
anchor.
Another manufacturing possibility is that foreground end face of the casing
is not bent right-angled into shape until completing the speaker wiring, it
is not fixed/spot welded at the corners, then you could use a standard
insertion tool.
Poor gain pot marked RE-AN
Bad send bypass sw, just touching vol control would return it sometimes.
LM3886T tr 14.2R//.4R , .4R
.33R, 2x 270R
3 spring tank 32R, 195R
R35 slight discolour 10K
R36,R38 probably 2K7
Loose IEC earth crimp
one white w/w not glued to pcb
As per tips files cordage stretched over the bypass switches, either side of the upward protruding
conductor parts
Marshall Guv'nor , 1989 foot pedal
Bad pots
Marshall JCM900, 4100, of 2006
Set as LOW and 4/16 switches
Dead amp. nothing on sp if test signal applied to RETURN.
1V 400Hz in , .34V at SEND
Broken 220R end of tank. Scraped back tail laquer and broken at
solder . Cut the tail and bend away from plastic to tin. Tinned
copper wire to pin and bent and tinned to join the open tail.
fingernail scraping over repaired reverb tank, 2V or so over 8R speaker
All fuses ok including pico and whitman.
o/p tx 16.8/17.1R
1/4 so. contacts ok. Normal mains current draw
2x290V HT on V3, cathodes come up to 42V.
It never looks right,to me, to use 1/3W anode dropper resistors, even if high voltage type. Did Marshall stop using HV types, these are light green body if suggestive of anything?
100K open circuit one to V2p1. 2x seriesed 47K 0.5W will go back in there and its mate.
No discolouration to the coating, scraped back coating and normal under the axial sampling I scraped off ,dark grey MO spiral, failed at one end. To last but 2 turn measured 63K, to last turn before end measured 110K. Presumably failure by gradual oxide breakdown by micro-arcing and thinning and resistance increase.
Another problem waiting to happen, especially if rough handled/knocked on front. There is a sub-front panel in these , rivetted to the pcb. Unnecessarily long landing tongues protrude across the pcb and their edges are about 1mm average gap to component leads, gap to one resistor about half a mm.
for comparison the other 100k measured a normal 100.5K
EL34 bias -47V
after repairing 100K and all pots at mid
chA .1V 400Hz in , 2.4V over 8R and .18V on SEND and
0.42V on RED test point
chB 0.01V , 400Hz in 3.2V over 8R,
.23V on SEND and .55 at RED
Marshall JCM900 , 1989
Bad vol and distortion
Broken i/p socket and ret bypass sw bad
no neon
Release bass and sensitivity nuts to release sub-front
made up replacement handle cover as per tips
100R chassis ground to speaker
C&K (2) USA V-series 5A,250V / 10A 125AC
maybe C&K 121
Squash cover section with vice jaws on long side until small screwdriver in join , nothing springs out.
The retaining lips are on the long sides of the cover pointing outwards. Internal part of the cover
is about 3 times the exposed width
4 (16) 8 impedance select
Don't forget 1/4 in so washers reassembling
Tx 5.4R// R-Bu 14.5/ R -Bk .1R
Marshall JCM 2000, 1998 ? (also see DSL50)
Latching switch types ok for VCRs etc, with tight clearances but not here. 2
DPDT worn , leading to problems unless you hold the knob in
or out. There is about 2mm of play between the knobs and the holes in the
metal of the front/rear panels. Replace those 2 plus 2 more with same
3.5mm pin spacing switches but ALPS make.
The 2 off 4PDT switches maybe more resilient to off axis loading so will
leave as is , unless anyone knows better.
yellow stem "angle with an F" logo, found 4 ALPS marked
ones, blue stem replacements and some slightly larger diameter knobs.
Required slightly opening out the "gold" fascia holes but not the underlying
panel and unfortunately red in colour. Permanent black felt marker over them
, cooked in with hot air and repeated again sorted out that aesthetic
problem.
The easy fudge would be peripheral cut a 5mm LED clip or 8mm with a section
removed fitted in the gap , but enlarging the fascia hole a bit, and
gluing-in the clips internally. The other problem is the black knobs seem to
be pushed on the shafts, hot, rather than gummy glued on , so do not come
off easily. To remove knobs squash diagonally in
a flat jawed vice. They always seem to split , once, a disguised seam,
looks more likely ?
Definitely mark all cables and wires before disconnecting from the boards.
springline 198R/25R
2x 4.7K,1K, 2x 10K, 2x 4.7K 0.5W, 2x 1K, 3x 270R, 3x 100, 2x 1R
rear 100R, 1K
mains tx , no valves
p 6.5R // purp .1, /blu 1.5,1.5 / o,r 23
o/p R.O .2 / gn bk .4/w 79 pur 40 bk
Marshall JCM 2000, 1998 dual super lead
mains fuse black and sputtered
Blown primary of the mains Tx, isolated removed from chassis, draws 1.2 amp
at 20V variac "mains" and temp climbs 20 deg C in 4 minutes or so.
Secondaries measure l27V, 16.3V and 2V so that side presumably ok.
DC of primaries measure 1.2R and 2.2R // secondaries .1R, 4.9R, HT 13.6
Pr Bn,R1 (failed section) R2, Be
Sec P, W1, Y, W2, Bk, R1,R2, N/C (heater centre join)
Normal single filament winding. Normal failure mode , for slapdash wound Tx
these days. Slipped turn at one end of a layer dropping into a lower layer,
then presumably chaffing of lacquer to marginally spot weld. Not at all
obvious "weld" point , about 80 turns from lead out of outer primary. 195
turns in all of .75mm wire for one 120V primary. Not a problem here as 240 V
use, but would be for this Tx used in USA . There is tape covering the inner
primary but not extended at the leadout point of the inner primary so first
turn of the outer primary directly crosses that point so a full short is
very likely there with a bit of normal in service vibration/ chaffing. For
240V use those 2 points are at near enough same mid-mains potential (2 tails
to options bridging point on pcb)
Marshall replacement £46
For balance I got a quote from proper tx winders Majestic , just down the
road
http://www.transformers.uk.com/brochure.pdf
for a one off , custom/semicustom build from scratch , to specified V & A of
the 3 secondaries. Somewhere between 50 and 70 GBP plus VAT plus carriage,
about 2 week turn around
Added a 12V 1.5 inch fan at the Tx. Using the unused heater tag for main
mount of the fan to solder a solder tag then that bolted to the fan.
Setting fan at 20 degrees to the horizontal and cutting and fitting a
shroud from that red impregnated cardboard stuff to direct the flow into one
side , up, over top and back out the other side between windings and bobbin.
As secondary side gets hotter than primary , fan positioned mainly on that
side
Air flow checked using a joss stick. Perhaps next time using some DC from
the amp rather than bridge rect and cap off the heater supply as light
current drops in the diodes bring it down to less than 9V . Retained the
template for the shroud for the next one of these to attend to.
Decided to power from 26V on 270R R22 via 200W 2W and 470uF
Tank 235R , 89R 4BB BC1D
o/p tx 14.8,15.2// <> .1,.1
20mm heater fuses Littlefuse 6.3AE250V helical wound wire approx 50 milli-ohm
so can use to check millivolt drop comparisons
Marshall JCM2000, DSL50 of 2002
Owner rarely uses anything other than green clean ch.
It dropped in output so instead of his usual 2.5 on the dial , needed 8.
Found the usual sort of problems on input socket and output speaker current switching ground contact and a switch but nothing that will bring the gain up in clean, from the output it was giving whan I received it.
All valves test good and balanced, same set for 6 years of use.
Some test results with 0.05V rms 400Hz in (600R SG)
with all pots at mid and all switches out (except the clean/crunch etc where necessary) and grids of V1 and V2
........... Clean ........... Crunch
o/p 8R 0.5V 7V
send socket 0.01 0.16V
V1(p2) <>0 <>0 (comes up to 0.2V on red and 0.4V red +ultra gain)
V1(p7) 0.05 , 0.05
V2(p2) 0.046 , 0.74
V2(p7) 0.01 , 0.18V
Anyone see anything awry there, seems ballpark to me?
I suspect a problem has occured in his Marshall 1936 cab , that I've not seen. 2x 16R AFAIK. He's using 8R on amp output and cab input.
If problem with input diverter contacts or wiring or one speaker and now running one speaker only and so 16R from 8R then a 1/3 constant volume drop makes sense.
Any test an owner can do without lending him a meter?
1.2V or 1.5V battery contacting the speaker lead jack, could you tell whether 2 sound sources under the grill cloth , by listening?
I would push a thin rod through the grill to touch the cones , in turn, but not something I could advise someone else trying
I asked if he'd tried his guitar and lead on another amp+speaker, and no. Would not failed wiring/pickup show itself as a change of sound issue? as well as level, especially with someone using the same guitar for more than 6 years .
Signal pin of input so. shifts under small blade twisting under, replaced with wired in . Corrossion on 1 way of the clean/crunch sw and as one
unused way, jumpered across to that.
Marshall JCM 2000, DSL of 2003
JCM2-00-06
Hum particularly on clean channel builds up from nothing ,over half an hour,
and very intrusive 0.3V rms of hum over 8R speaker load and still rising.
Putting a signal in Return, for PA only, is fine but opening guitar input
hum returns.
Owner had replaced all the valves and exactly the same hum.
Hum is negligible on the downstream HTs from HT1. What sort of grounding
problem increases with warmth?
C13 100V 1uF at V1(A) cathode , of all things, is highly sensitive to hot
air.
Monitoring the hum over the output load. Once force warmed and hum level
risen it is reluctant to go down again from natural cooling or from freezer
spray - what process is going on with in it?
pots at half
after 20 mins 130mV of hum over 8R load and 900mV after 30 mins, simple DVM acV
measurement, still increasing
Allowing the whole amp to cool for 1/4 hour obviously resets the effect
It would be nice to find a schematic for this specific variant , but only
one Google Ref for the number on the end face label
JCM2-20-06
I'm wondering if there is any significance in the bodged 1/3 W R
replacements
R70 of 5K6
R7 of 5K6
R48 of 100K
unfortunately none of these numbers agree with any JCM2000/ DSL schemas that
I have.
The valve set that are in here are all 2009 , he took out the new ones and
replaced these used ones. They look brand new except for simple dragon's
teeth marks, ie not repeatedly moved around.
The Russian markings are quite visible and there is no sign of overheating
of the bases , still light brown , and the pcb around looks as new.
But the first thing I will do is check for o/p bias drift, then heating the
pcb with hot air and a 2Gohm megger and then remove V1 and see if hum
returns then replace and monitor DCs around V1 on heating ,
http://www.lynx.bc.ca/~jc/TSL122.html
No mention of that Marshall Forum page about hum but it could be these pcb
problems around V1 the immediate problem
main bias results
monitoring every 5 minutes for the first 15 minutes
rate of increase is falling
passing 10 to 15 minutes in
one side rising 1.0mV per 5 minutes and the other side 1.5mV per 5 minutes
starting from that 15 min reading of 76.9mV and 68.2mV should be about 90mV
over an hour .
locally heating with hot air (low setting) for 20 seconds the voltages shot
up 5 or so mV but soon dropped back to where they were , unlike the problem
around V1 it would seem.
No E number of board supplier found but I would say, by trying to press a
needle into the board, it is epoxy rather than polyester composite.
Megger showed nothing untoward
With no V1 in place , the grid socket pins measure about 10 or 20mV DC, wave
hot air over the valve base and the readings shoot up to 100 to 200mV, just
like applying a magic wand.
The cathode lines have 2/3 orders of magnitude lower resistance to ground so
any such effect not so obvious there
These are the small bottles not the hotter big bottles, something to do with
that metal shield plate for them? I'm assuming the effect is at the valve
base through board , hot pins rather than where the anode dropper leads pass
through the pcb, and passing through rather than along the surface . I will
explore this, as hard wiring the HTs to isolated valve bases ,only, is quite
different to hard-wiring all HT traces.
Now what is the physics /chemistry of all this ? I assume something
hygroscopic is grabbing moisture then forming a conductive salt that stays
within the micropores of the surface of the glass fibres, but why
temperature increasing the conductivity , what salt has highly temp
dependent conductivity, we're only talking 50 degree C or so
I'm just wondering if this particular board , only 1 google ref, that they
will not have a replacement
Why did the mod-bods choose to isolate the grid pins rather than the anode
pins?
I can see run away bias , less neagative grids with temperature rise being
caused by conductive epoxy. But as I say (for the moment) this amp PA seems
ok, but where is the hum coming from around V1? some conductive path from
the heaters?
Anyone know if they use mineral filler (cheaper) in the epoxy of epoxy pcb
manufacture. Like the use of calcium carbonate in the epoxy bulking/fixing
of toroidal transformers or even car body repair filler.
This morning I made a test cell of some calcium carbonate and water to thick
paste consistency in an inch wide plastic bottle cap. Resistance across a
diameter about 60K. Waft a low-setting hot air gun over it and resistance
drops to about 2K, now rising again.
So moisture/condensation can get into the edges and component holes of such
a pcb and the glass dutifully conduct it capilliary fashion.
Perhaps a cure might be a low oven bake of a day at 105 deg C of a populated
board , assuming nothing comes to grief at that temp and then some sprayed
on conformal coatinf along all edges and component leads, but that would not
get to the prime source of problems , inside /under the valve bases and
those pcb holes
For an owner who knows he has such an amp, this would be worth doing.
Obtaining or making an amp sized heavy duty polythene bag that can be
resealed easily and some sachets of activated silica gel crystals and a
large jam/pickled gherkin jar to keep the oven acivated ones in, until use.
After each use of the amp , place amp while still warm prefereably ,in the
bag with a fresh sachet from the storage jar.
A day on of drying out and my test cell showed 150K, warming easily brought
it down to 10K.
Tried a sample of calcium carbonate as it is , powder straight from the open
bag a decade old at least , and no response to a megger.
My chemistry failed. 30 percent HCl showed no fizzing with the powder.
Warming up and a lighted taper extinguished in the tube.
Ground off a sample from this Marshall board and the same.
But then tried a tube of HCl on its own and same extinguishing of taper.
I'll stick with the day job.
Long term left a cap with a small amount of common salt mixed into calcium carbonate
with 2 aligator clips eith side and left on a window sill. Every now and then I'd test it but
always >500M , then middle of damp winter the cap started overflowing as though it
was diecttly under a leaking roof. Low kilohms and dropped with warming.
Some op & V1 readings , no signal through, over about 15 minutes
o/p hum 3mV, V1 cathode 1.82V dc
18mV, 1.870V
45mV, 1.847V
80mV , 1.848V
143mV, 1.861V
R19 to R13 to V1p6 dropper chain
R28 (22K) to R22 (2K2) to V1p1
Large pk on steel plate under the valves needs spring washers
Reverb tank , black phono to front of amp
red wires W13 ? on the mains Tx somewhat loose
Started with 4 cuts with Dremmel and small .6mm disc around the grid pins of the
pcb but 3 cuts each are neater. But desided still looked horrible and made a hollow
cutting tool , see tips
Rewiring node plot and this 06 board variant
V1 p7, 68K and p2 to con3 , 10M
V2p7 33M , LDR1 here replaced with 470K and LDR2 again replaced with 470K ,/ p2 470K , 470K
V3 p7 100K, 47K, 47K / p2 to anode p8
V4 p7 1M , 22nF / p2 1M , 100nF
With modded pcb
With 60 percent mains , mid pots , sw out and no valves in place
V1 276,0,0,2.3,2.3,272,0.0.-2.3V dc
V2 276,0,0,2.3, 2.3,276,0,0,-2.3V
V3 279,276,0,0,0,276,0,0,0
V4 276,0,0,0,276,0,0,0
with those 4 valves and 60 percent mains
V1 244,0,.09,1.7,1.7,162,0,1.7,-1.7 V dc
V2 212,0,.8,1.7,1.7, 218,1.4, -1.7
V3 259,221, 39,0,0,221,0,.3,0
V4 180,16,25,0,0,187,16,25,0
With 4 x EL34 in place and 70 percent mains , mains draw was climbing to
1 amp so switched off
DON'T FORGET TO REPLACE THAT SILLY DOUBLE PRESET BIAS BOARD
Back to normal
To test the board in the Dexion cradle need to make 3 or 4 long standoffs
to hold the pcb in place, fitted to available holes in valve bases/ pcb and dexion
and suitable pad out washers, used daisy chained stud and hole hex pcb standoffs but
something more rigid and stronger would be better
Returned a year later, no return of hum problem but now a distortion of
higher f components when in "dirty" channels, fine on Clean.
When inside crackling induced touching R18 so replaced.
Completed isolating the grids of V1 and V2 lifting R29 and R30 off the board
R18 +X and cut trace at R15 + Y.
Some remnant pcb material remained around p2 and p7 from previous so ground back
with poiny "diamond" bit.
On reassembly and testing, large curren draw from mains, I'd trapped
a couple of wires between the biasing pcb , between the valve carrier panel and
chassis proper and punctured insulation on tightening the sc.
Swapped V1/V2 and V3/V4 JIC
Marshall JTM/1962 , of 1998, amp clipping
Output ok up to 1 watt out then output clips both sides of sine. All valves
test fine for gain and internal leakage. Signal is fine up to the wiper of
the treble, ie before the splitter/driver, that signal stays sine well into
clipping of the output. Changing the splitter is the same. Running at
clipping and dropping the HT via variac makes no difference , changing
output bias makes no difference to the clipping. The splitter valve cathodes
measure about 34V and the grids about 23V at point of clipping. All the
surrounding Rs measure ok. Output Tx primary measures 139R red to white.
Capacitor problem? amp was subjected to a knock that dropped the output of
the rectifier valve , since changed, a session before this problem emerged.
v3p1 anode is 220V and v3p6 anode is 168V so leaky .1uF letting through some
of the neg bias from the output bottles , I assume
I may as well try removing the output valves and trying on 80 percent mains
or so ,and check their cathode signals, but looks more and more like a turn
or few , shorted turns in the Tx
swapping output bottles did not swap the problem side.
Trying a 600 ohm sig gen backwards into "8 ohm" so about 50mV pk-pk there,
0.36V on the (from low V3 anodes) problem side "white anode" and 0.5V on the
red other . I assume they should be much closer than that. I suppose the
conclusive test is swapping red and white wires and see of the low splitter
V3 anode voltage swaps halves.
I forgot about the feedback and simply swapping white and red creates an
ultrasonic oscillator via the phase change. Changed that .1uF cap and same
clipping problem.
So nowhere else to go , I may try disconnecting the feedback , take some
readings with red and white in correct positions and then swap white and red
and see if the problem side changes.
I forget whether measured cold or warm but 61.3R and 66.4R, which seems
normal enough, will try again cold and also with a 1KHz RLC for "R" and L
of both
a corroded break rather than shorted turn/s? now taking Tx readings
DVM White 61.8R , Red 75.3R was 61.3/66.4
RLC(L) 20.9mH, 34.0mH
RLC(R) 215 imp, 338 imp
Things certainly not right but what is wrong inside? tugging the tails makes
no difference
paint stripper dabs on the pcb mounting nuts/studs
Bias voltage at 220K/220K junction, -37V
332V and 254V on R29
Marshall JTM "1962" from 1993
Working order but for bad pot, but some things are not pukkah.
Reconned existing pots
The main carying handles, presumably original as no other holes, are just
held with woodscrews into thin carcass wood, splintered away internally, as
no pilot holes drilled, - replace with nuts/washers and bolts?
The screws that hold the main lifting handles have very jagged exposed
head-slots as though the windy driver( or bad human) slipped on driving each
one, so replace with bolts for that reason alone.
Owner is in the habit of going around with switch cleaner for the jack
sockets so I will beef up the contact closing force on all those.
So did the rubber cord beefing up of all 7x 1/4 inch sockets
as described in the tips files. Bad soldering on one wire of the
input sockets
Finally there is the ridiculous system of casters on these sort of Marshall
cabs. It is quite possible for all 4 casters to end up pointing inwards so
the slightest of tugs on a guitar lead will pull the cab over. A 9 inch deep
cab is then relying on just a 4 inch wide wobbly footprint but still 26
inches high. Especially if used on a carpet.
Jacking up the innermost edge of each caster.
So the self weight should bias the casters to pointing outwards when at rest
, for maximum stability. For normal in line carriage then the change of
orientation , via the cant, would have to lift the cab and hopefully that
self weight at rest would return the casters to outwards position. To turn
inwards would mean itself, unassisted, increasing the height of the cab at
that corner so unlikely.
The canted casters work well.
They are not the original , part recessed ones, presumbly busted off years
ago and replaced with standard hardware store ones.
Canted casters
Propping up on one edge with doubled up rubber feet used for kit, so 4 to
each caster. Uncompressed feet stand off height 13mm .
Original gap between base of cab and floor of 69mm and still that with feet
pointing outwards and 83mm if both pointing inwards.
The action to get all 4 feet pointing outwards could not be easier.
Run the cab on all 4 casters in the longways sense of the cab , go 4 inches
further than required and pull back 4 inches.
The transporting action is worse, in the wayward supermarket trolley sense,
a mind of its own, so perhaps only one rubber foot per standoff rather than
2 or transport using 2 casters and one of the main lifting handles rather
than the top movement handle.
Another advantage is the casters then end up an inch or so ,
each side, further out for an even more secure "wheel base".
Uses J174 fet, 2x 160R, 2x 10k, 2x 470R.
Parallel 190 ohm speakers , 6R, DC.
Dummy load test with 3.25x7.25 ins plate resting directly
over the main bottle clamp rings
then temp took 35 minutes to go 44 degrees C over ambient
with 400 Hz, 4V ac into 8 ohm , dropping 0.5V ac over 35 min.
Marshall JTM , 1998
In conjunction with British weather/ garage storage.
Well I can't believe I'm unlucky enough to have 2 such repairs.
Earlier one Marshall 1962, year 2003 bluish-white flash from the HT area of
the mains Tx secondaries.
Small arc over just 1mm or so , moving the wires apart and cleaning and
telling the owner to store the amp properly, cured that (or at least did not
bounce back).
This time Marshall JTM Tremolo 50W , 1998.
1962-20-07
Joanne Betty QC tag inside
Generic problem with Marshall valve amp mains transformers?
The giveaway is that the HT fuse
failed at switch off to standby, mains sw on. Replacing fuse and running up
on a variac amp would work fine up to 95 percent mains and switching back to
standby but 100 percent and switch to standby and Tx saturation noise and
dramatic long bluish-white arc from near an HT(ac) terminal. As fuse is in
the ac line and the o/c voltage goes up on removing the load on the valve
rectifier at sw off.
Between the purple "o" s on this pic,
http://www.diverse.4mg.com/Marshall_jtm_tx.jpg
vertical black smudge presumably a carbon track. The wire removed from the
red tag by me, 2 wires to the black ground tag. The black mark and the 2
bare copper patches lie along the edge of the nylon , the o-o line , not
distinguishable in the pic. As the wire is .27mm diameter you can see the
"carbon arc" was 2.5mm or so long and colour white, not green or blue.
No obvious organic mold marks elsewhere on the amp or even abnormal rusting
of the steel bits.
Any opinions on the derivation of this problem. I assume marginal invisible
mold growth that carbonise over amp use, and chafing? and 500V or so pk-pk
then carbonising of the nylon or Tx lacquer.
Hopefully recoverable by cutting away/cleaning nylon and silicone sleeving
over the wire and exrending to rejoin the tag, to move it away from the
edge. Would there be some Marshall treatment/coating that may promote the
initiation of this problem? yes I know its due more to owners than
manufacturer
Whatever it is, spider piss/ mold or whatever, "chooses " this one edge position on the outside of the Tx,
or 2 out of 2 occassions , I don't like coincidences. Condensation/damp I
would have thought would make its presence felt well inside the windings.
There must be closer gaps inside to ground than this 2.5mm . I know high
voltages like to discharge from/to sharp points , is that what is coming
into play. Perhaps the nylon moulding should have rounded edges,
a/ to lessen scuffing of the wire covering,
b/ lessen HV discharge possibility.
2.5mm is an enormous distance to jump in normal circumstances for 500/550V
Basically what facilitates corona discharge, relevant to this particular
position
I think the edge is the key to it, it was that edge previously but the
wiring spacing was nearer 1mm than 2.5mm. As in that pic there is only 1mm
or so spacing between those 2 wires with the pd across, farther back to the
core, but its on the flat there.
I somehow don't think mold would go for edges, and similar I don;t see
spider piss would concentrate at edges. I once came across a failed scope
where the smps would not power up. The isolation of the opto-coupler had
failed because mold had grown on the glass sliver between each side and then
became conductive, scope stored in a shed.
Sleeved and moved/extended the wire away from the nylon and its now back
working without flashover/ blown fuses and advice to the owner not to store such
equipment in UK garages
Mains Tx 7.8R, sp 6.7R of both in parallel.
HT secondaries 38R and 41R
Owner dropped the amp on removing from the cab and knocked the DD tube.
Low HT1
With 2x4007 in there then 380V dc
with the Marshall marked GZ34/5U4? in there and 400Hz input,HT1 of 316V with
.05V ac over 8R, then drops to HT1 of 257V with .47V over 8R and clipping distortion
With good GZ34 in there HT1 drop sfrom 383V to 366V with the same change of input signal.
Testing on Avo tester the bad was D1 19%, D2 21% compared to 2x 75% for a good DD rectifier
Marshall 1962, 2003 as M2003 on the bar code labels, but owner reckoned earlier,
repaired by Marshall 2003?
Operator initialled internal labels by "Jena M" , Halson, Cruilshank
Looked more like 1970s as had been kept under a tarpaulin in an English garden for a year,
as they got fed up with it for blowing fuses in use. Arrived with me as dead, immediate reason
was someone must have turned the speaker ohmage setting to a nul posistion thinking it was
a fuse housing, both user fuses fine.
2 Celestion G12M, one had failed due to corrossion in the VC/magnet gap catching
the VC wire. 10mm run of .18mm wire, 2 layers,
Good speaker (so far?) 12.5R
Removed the cone and removed the last/middle 6 turns of wire at the open end. Stripped last 3mm
of wires , twisted, soldered and squashed in parallel jaw pliers and last turns run to former
and around the solder some RTV glue.
approx 840mm of wire removed , 45mm diam, so about 5.4 percent of VC removed so about
.67 ohms. Added .6R/5W vitreous resistor in line , solder to tag terminal and other
end through drilled hole in fibre board and other pigtail returned to that.
Choke 103R
o/p Tx 77/78.7R
Mains tx 7R3//.1,.1,40.2R-B-37.1R
Lower i.p so jumpered between I and II inputs
One of the 3mm pcb brass nuts and starwasher loose inside.
Release all pots and 4 ip as a string, label inputs JIC.
Desolder the black wire to the choke, to inspect solder of pcb
Considering all those personal names of testers/inspectors labelled inside.
a 1962 from 2003. A history of blowing fuses then would work for months then
blowing again. Is there a name for them , the little bits of wire of
cropped-off component leads. Anyway under the tremolo valve base , probably
sort of spot welded just the solder blob end , to one of the tags. A 5mm
long piece of cropped off lead from a 1W resistor or similar. It could swing
across, as only vaguely atached, and short the tags between a cathode and
anode of V6 tremolo valve. I assume it was loose somewhere inside the amp and then bounced into
just the wrong spot and current passing was just enough to just "solder" in
place on the first shorting excursion
Not really detective work. My repair methodology starts (after initial
powered up assessment if appropriate, then dismantling) with a full viewing
under a x5 illuminated inspection lamp+ bulbous lens. Noting unusual device
types, large R values if no schematic, state of solder joints, insulation,
discoloured areas etc. I just saw what initially looked like a non-cropped
off wiring-end ,through the valve base tag, ending too close to a pin 1 to
pin 7, bare cross-coupling wire. Up to then I was thinking mains transformer
interwinding fault.
1KHz ESR of main caps , in cct, .8/.8 and 1.3/1.3
With amp open one time noticed a small white-blue flash coming from the mains Tx, going from standby to on, in
area under the black and red HT wires near the neon. Hope it does not indicate why the DC ohmage
difference . With a needle, moved the exposed enamelled wires apart and never noticed a spark again
With all the pots strung together but not fully fixed into the chassis may result in low
treble through the amp.
Marshall JVM 410, 2006, PbF
Loss of volume , owner replaced all valves , cured that (? intimate contact with
valve bases probably temp made good ) then new problem
Reported as distortion on A of G-string on OD1 and OD2 not clean or fourth ch
Early and bad PbF but is it the problem here, most of the ECC83 socket
solderings were very iffy .
Volume dropped and owner changed the valves. Volume came up but a distortion
on the overdrive channels emerged soon after. Redoing those socket
solderings and usual suspects on front controls board has not cured the
distortion problem.
13.9R speakers combined
file down corners of Tx s
R81 touching R82
bad socket joints on V6,7,8,9
relieve screening can springs
schematic on elektrotanya
Harsh cut-off more like clipping and no sign of any smooth saturation,
rounding of the peak/s, just launches into cut off on the peaks (not
troughs). With all pots at mid posistion the signals ,clean and OD, are
sinusoidal and amplitude ratio of about 2:1 OD:Clean in the gain and tone
block. That preceeds the valve V7 which with mid pots and order 10mV amp
input 400 Hz has on pin2 , grid, about 100mV pk-pk for clean but 7 volt on
OD thence clipping.
All valves test fine, all R in relevant area are fine. A cap problem ? but
coinciding with valve changing? I've not inspected underside of that
wired-in board but I'm assuming a cap PbF solder problem. Vol drop could
even be the bad PbF at the input socket but problems appearing /
disappearing at "intimate" handling suggest PbF problems. There is loads of
relays in this design also .
I removed the main board and no obvious PbF problems found but treated all
the usual suspects, including S & R. I did note that the 1 1/4 inch fuse holders would have
failed solder in a short while.
not S/R loop problem
Just in case it was an odd batch of ECC83 , I tried with others and the
same.
Keeping same input and changing frequency
4KHz , 26V pk-pk on V7a grid , pin 7, and ok normal soft roll top "clipping"
2KHz, 48V pk-pk , bad trace hard clipping
1 K , 35V , bad
200, 15V bad
100 Hz, 5V, normal trace shape
so to find an errant cap that is involved in OD1 and OD2 channels
Tomorrow I think the 1uF on the cathode of the first triode needs exploring
as its output is upped in the 400 - 1000 Hz area. Of course a bit
exagerated, in that frequency domain in the clean channel, could well go
unnoticed.
V6p2 ok sine
V7p2 ok but V7p7 halve wave near enough
80 percent mains V7 dc
210.0.2.2,0,0,95,0,0.5,0
V8
251,95,94,0,0,250,20,75,0
26.3/24.8 con7
high signal side of R129 ok, low side distorted
Remove V8 still bad V7p7
330 to 210 via R75
R96 ok sine
R98 bad
R97 bad , all pots at mid
signal at con7(1&£) much the same od2 and crunch
150 and 350mV at CN7
1 1/4 in fuse holder problem
Pull on o/p Tx gnd of main pcb to release EL34 sockets, then 1/4 in sockets .
To reseat use dart point in EL34 mounting brass to lever each across in turn,
all a good way to mess up PbF solder points
For V6a grid of order 1nF added would supress gain in this f area but too little at 500 Hz
and too much at 2KHz
con7 gnd is GND-A connected via 100R .5W R107 to GND
Relay function matrix
1 2 4 3 (note order)
od2 H H H L
crunch H H H H
clean H L H L
od1 H H H L
low is on, H is off
201 202 203 204 205 206 207 208 209for same ch order
H L L L H H H L H
H H H H H H L H L
H H H H H L H H H
L H H L H H H L H
OD1 and OD2
Rel 3b on
rel2b off
rel4b off
rel203 L, od2 / H od1
rel 20? od1 and od2 low (on)
differences to elektrotanya schema
100R between GND-A and GND
R107 100R .5W
Marshall Master Lead combo, 1978
In for more basic problem, squeel on gain pot turning, but only a
Polish reference out there on this
All seems original in there and o/p devices TO3 Motorola, badged SCSP1 and
SCSN1.
http://www.drtube.com/schematics/marshall/2099u.gif
Darlington pairs, so they have much greater hFE than the
2N3055/MJ2955.
speakers T1632, B1, 21 // giving 3.1R
+/-24V , 9V over ZD1
18V over large electro, MO 8003
Bad pots treble, Normal and bright
Pulling the pot shafts tightens wiper contact but as curved , with corrossion
there then loss of contact.
Marshall MBC115 15 inch speaker lump
For 250 quid you'd expect some engineering. Just as well problem made itself known at practise power levels.
Large coil and 15W dropper on pcb which is only held to the mounting plate by the longish speakon and 1/4 inch socket pins. Bad enough with proper solder but a definite no-no with PbF, vibrating in a box.
Wired-in 0.25 socket will go back in there and punched pads of woven copper mesh in the other usual suspect remade-solder joints.
Could cut electrically isolated areas on the pcb and 2 little brackets but I think I'll give hot hot-melt a go. Rough,as possible, grind off the black paint and some undercut grind gouges into the steel as well . Then heat the plate prior to first run of hot-melt , gives very good keying that way. Then normal glooping of hot-melt to bind together to the pcb.
Next time remove the bar code label, its plastic , not paper like the RoHS and laughable QC ones.
Marked the exclusion area on the plate and pock-marked with a dozen undercut gouges with a diabolo ended cintride bit in a "dremmel", then ground off the paint in the relevant area. Hold the plate over a surface with 4 ptfe feed-through insulator/pins. Blob of water on the plate and heat with hot air until the blob has evaporated, then apply hotmelt.
You cannot pick it off with a fingernail, when cool, even picking off with a dart point is difficult. Fit the bits and hotmelt a bridge-over fillet. 2 more cable ties around the 1 looose cable tie.
Holes through the pcb and silicone rubber sleeving around the ceramic R, and reinforced resoldering on the usual suspects. And of course wired in a replacement quarter incher, before hotmelting . The archives are full of people annoyed by the lack of the "designed,engineered and quality conrolled by Marshall" printed on the plate of these and similar big boxes
3.8R bass
2.2uF 100V non-polar cap
mark and tie 4 wires so cannot drop into cab
Marshall MF350, Mode Four, 2003
Amp works on its own but no crunch channel via footswitches.
Failure of "D" connector pin, fine for intermittant pc use but not
repeated making/unmaking.
15 D pinning Bk common, Br OD1,-,R,O,Y,Gn,Bl
Vi,Gy,W,-,-,Bk OD2, Bn Rev
Hot melt over LED mounts and bare common switch wires near metal switch
bodies 4 momentary and 2 latching, and bare joint floating in space.
Replaced the solder bucket plug and swathed in hotmelt to
stop any pins moving rearwards, and checked the amp one
which is pcb mount.
Remove top section of rear panel, then top front panel
from inside, then 4 screws under and unstick the chassis.
Loads of dust in the gap between each pair of heatsinks.
Uses 4x tda7293, 3x 0.1R, green (I/C) 100R, 2x 10R, 2x 22K, 2x 2.2R near bridge rec.
transformer 2.1R // .9,.9 / .2..2R all I/C
15,-15,5V regs
power interconnects to prea
0,1.7,5,4.8,0 .1,.1,5,5,0
to valves -24,-24,15,0,0,-15 , 107V on link6 from stepup D array.
Bent inwards the flanges of the interconnect cable D
sockets for better screwdown.
Marshall MG 10CD, 2003
Bad input so. , tip grounding while inserted and bad dirty vol pot
Marshall MG10CD, 2003
Intermittant cutting out - fuse holder problem
Uses TDA2030 , TL072,BA4560
0.1 and 220 large Rs
26V ac , +-16V
Marshall MG15CD, 2002
Mains lead broken at gland. Mole grips to compress old one to remove.
Replacement ground back part of the interior intrusions so not so deforming.
Mole grip compression to reinsert.
sp 6.3R
4 flat "point" sc for chassis fixing ,pointed for wood fixing
Marshall MG15CDR, 2004
Volume intermittently going to maximum
Due to the bush nut for the input socket falling off any
plug pushed in strained the pcb with result that ground side
connection to the volume pot failed.
Also a plastic cover over the springline suspension plate
had fallen off and laying over the springs , needed putting
back and held in place with cable ties wrapped around.
Uses LM1875T , small w/w is 0.1R
Marshall MG15DFX , 2002
mains lead broken at gland
open up the inner surface of the replacement a bit before replacing , so the cable is
nmot so squashed and also easier to unsert, but still holds cable from rotating and pulling out.
sp 6R3
pointed sc rear panel, othe r4 for fixing chassis
Marshall MG30DFX, 2003
Bad effects gain control, maybe spindle
grease migrating and off centre wiper action.
Bad speaker crimps.
0.1R, 2x 100, 2x150, 33
Marshall MG30DFX, 2004
Intermittently drop in volume.
The spring clip had failed at a bend
that retained the 7805 to
the heatsink shared with the TDA2050.
Replaced 7805 just in case.
At some point the heatsnk had seriously overheated as
the hot formulation hot-melt glue that bound adjascent cap
to the board had remelted and spread under the heatsink.
speaker 3.6 ohm dc
Input switch weak so reinforced with silone cord and Hama.
the line out socket has the ground line switched and this
was dodgy from grime.
With 400Hz in giving 2.5V ac
into 4 ohm dummy then heatink gained
and settled at plus 46 degrees C in 20 minutes
and dropped 0.05V
Marshall MG50DFX ,2002
Cuts out intermittently
Tx 26.2-0-26.2 / 10.2-0-10.2
speaker 6.8R
22R// 1.2R , R-R, 9R4 bl-bl
Tip sw on footsw bad, 50 to 100 R
Marshall MG50DFX ,2002
CD ip fine but guitar ip cuts out
rear f/s and ret bypass sw corroded , also ch select sw but unused contacts bad
DSP pcb nuts loose
remove pillar near Tx to remove main pcb
Replace 1/4 so with proper so wired in upside down
Marshall MG 50 DFX
repeated loud bangs on switch on
Only about 2 years old, solid state.
Series of loud bangs , about 2 a second, for a variable number of seconds
but about 10 or 20 seconds calms down to normal.
Only at switch on from cold, off and on , minutes or even an hour later ,
there is no bangs.
I originally thought it was due to broken input socket so the input not
shorting with no guitar lead connected, was open circuit, meant the input
was unterminated.
Replaced the socket with a more robust one with functioning switches but
because powering up quite soon after initial powering, with me, this symptom
did not appear on soak testing. Returned it to owner and of course a few
days later and they powering up and bang,bang.....
It certainly sounds more like DC surges.
Its annoying having to wait so long for electrolytes or whatever to reform,
degrade or "plates" deform to be too close. With these amps its possible to
disconnect all lines to the output decice and associated comps. After
leaving overnight and powering up, this morning, monitoring the line out
there was nothing wrong at power up, so preamp opamps probably OK.
I Let the DC rails fall to <02V after switching off, Reconnected the output
stage and switched on and bang/bang....
Suggests a problem at the output.
Replace the small 47uF,63V secondary DC rail electrolytics on this
output board and left a few hours before powering up again.
I cannot see what chemical ? problem there could be inside the TDA7293 that
would take hours to reform.
One of those very enigmatic faults.
The 3 caps are on main +- rails and the bootstrap facility
Changed all 3 caps and now a continuous high level buzz for always , no
normal function however long amp is switched off.
Put a higher ohmage speaker on output for a bit of leeway. Monitoring the
stand-by line there was high amplitude oscillation during the buzzing.
Cutting that connection allowing standby control i/p to go low then muted
the o/p, as should be. Taking it high via a 3V battery and normal service
resumed but whether the original fault is still there plus some feedback
low-f oscillating loop involving the stand-by control ?
Ther's no oscillation on the downstream side of the cut standby connection.
Put 47uF on the standby line and it gradually ramps up to about 6V which is
presumably as it should but no oscilllation.
Tracing the circuitry back down the standby line and hopefully find a duff cap there.
It seems as though there was a very small soot jet on the pcb tracing back
to the collector of the little MPSA06 buffering the switch-on hold-off of
the standby control. Otherwise cold "diode" checked out ok. Uprated that
and associated 6.8V zener and 50V, 220uF cap.
Marshall MG 50DFX, 2004, 17Kg
Nasty noises due to failure of input switches in
1/4 socket, lost spring action to close.
Replaced with a metal barelled socket upside down,
wired in.
The earthing ring removed , hole punched larger
and used on the replacement as a complex grounding scheme.
Hot melted into place against the board after placement
in the front panel, for anti-rotation reason.
Uses TDA7293 with fan, 7815,7915,7805
resistors 10, 0.1, 2x4K7
Marshall MG 50DFX, 2003
Autumnal musty fruity smell
Bad buzz, sometimes no output, clicks and bangs and
sometimes works properly.
Someone must have thrown a pint of cider into the
fan vent, inwards blowing fan. Heatsink protected the TDA7293 from being
spattered but 6 faults found (so far), dotted around the amp.
Washed boards with meths, redid solder points where there was sediment etc
Problem on the "ribbons" cleared, put alternating set
on the headers and reversed end-to-end the cables.
The heatsink is isolated from the chassis but
something must have been slightly conducting as
-38V (on TDA mounting plate) would go to -28V )38V +rail)
when the buzz was present. Placed mica and insulating
mount to this tab.
C80 loose
bad master vol pot, gunge under the wipers
Tx 21.5R// 1R,9R
2x 3.3K, 2x 4K7, 220,10 2x 3R2, 2x 470
digital power devices
marked 32AB N12A and 27BL N05A
pots A20K,a5k, b20k
a1m,a20k,c100k,b20k,b100k
C type is reverse log so replace with upside down b type ,
wired in straight rather than crossed.
b5k,b5k,b5k,b5k
The heatsink is held by cup covered-head screws.
low vol FX return bypass sw intermittant and way5 of rear board umbilical connector bad.
Marshal MG100DFX, 2003
Loss of digital effects, probably a stock fault.
Small square digital board held by 3 plastic standoffs
but the "permanent" through main board anchors are made for
a thicker board and 2 of three were loose and of that one one of two
tabs only working. Pulled all tabs out with a needle-point
and hotmelted in place.
One wire link bent so only a few thou from its neighbour
Probably PbF from LTSIT (Low Temperature Soldering Iron Test) and coned appearance
Solder for the mains fuses would have failed in a few more months time .
Input socket tip would have soon caused problems.
mains tr 9.7//.7 (30-0-30)/1 ohm (10.2-0-10.2)
2x 2k2, 2x 4k7, r1,10R, 2 x 2k2, 180k
TDA7293,7805,7815,7915
Digital board marked 694V SMD tr topcodes 27AE/N05A and 32AH/ N124
TMS320VC5401
in circuit Fluke DVM diode readngs to ground along connector
0,.67,.91,.97,.67,.32,.67,0,0,1.83,1.83,.54
powered DC, 0,3.1,5,3.3,3.3,3.3,0,0,0,0,0 controls at max
pots A1M,A20K,A5,B20,A1M,A20,A5,B20,C100,B100,B5,B5,B10,B5
Marshall MG250, 2006, RoHS
Vaporised fuse from beer thrown into the rear , so in fan vent and over the PA heatsink
which is otherwise isolated by the plastic fan , at main neg rail voltage ( beware of testing
one amp etc while dismonted)
Replaced fuse at at 30 percent mains >2 amp draw and buss in speaker
With both PA unplugged normal mains draw at 100 % mains, shorted (well low ohm)
outputs of both TDA7293
These are eyeletted so .5 mm disc grind through the pin bank and desolder singly.
As blown tracks on one , replaced other amp and tried it singly in both headers to check
the preA etc, swapping speaker outlets. On DVM diode testing the other before powering up, lack of diode reading betwen main rails,
solder break to the track at p15 topside of board.
Locked the 2 o/p pcbs together with a short length of hotmelt rod so
they cannot rotate if single fixings loosened
Tx 10.6R // 0.5 r-r, 1.1R b-b+/-35V rails
sp6R4 and 6R7
Marshall MG250DFX ,2002
sp 6.7R and 6.8R
After 10 mins cuts out, sometimes nothing at sw on and headphone o/p ok.
Bad bypass sw on rear
Hot Rs 470R and 680K ok
replaced 2x return 1/4 inch on rear.
Bad ground to input as bush nut tight but buggered , wired in with star washer to
gnd of replacement wired in socket
4 wires to ip so, as switched gnd and tip and fixed star washer gnd.
Remove grill (4 plastic washers under) and clean fan blades and under fan , in situ.
Could see small white arcs at mains fuse not appearing on the sound out, on twizzling test of main board, weak
fuse holder.
Marshall MG250DFX, 2008 PbF
I'm not geting a consistent story from the recording studio where these 2 Marshall MG250DFX came from, with
Eminence 2x12 in each. One amp , one of the headers was partially disconnected for the power and signal to one
TDA7293 PA. Would this be a possible scenario. TDA o/p driven to DC with loss of one rail and burns out one of
the speakers but as music still coming from the other, not much thought about it at the time, perhaps reporting
smoke/loss of power to someone at the studio. Then someone with the studio jumpers back-to-back that amp to
the speakers of an exactly similar amp, and blows the mirror-handedness speaker of that combo.?
First one seriously burnt up including part of the spider, but the second one barely had time to get warm before
the wiring of the VC fused o/c so not even any scorching on the VC former , but a neat split. The first blown
speaker due to intermittant DC and then the second full on DC drive?
I deconed the second speaker and the magnetic/DC current force was so great it axially split the former of the
VC, beyond the inertia of the cone, tearing the VC tails and so fast that not the slightest trace of any heating
anywhere
I wonder if there was no real bang if the cone had no chance to move any air, and there was little more than a
ripping noise
Loose mains Tx swivelling on 1 bolt only , edge of Tx punctures plastic
insulation of 1/4 in spade to IEC and flash/bangs. Apparently a dispute with some band and someone removed the amp ,
removed the bolts of Tsx of one of these amps and fitted back in the cab. the other one just slightly removed a ribbon to a PA
and replaced amp in the cab.
loose h/s bolts
bad sp outlet so. soldering, looked good but with a flat blade between pcb
and protruding lump to housing , no force required to pull through
Eminence sp 8PKR-90011
all sp bolts loose, so add star washers
Blasted off VC 2 layers x32 turns 9mm wide,45mm diameter, ,2mm wire.
Lifting spider , paint brush and paint remover, stayed put but
removed the black enamel of the basket, next time allow to soak in over night
Charred R105 , 10R
Bad gain pot so excessive gain except at 0
Microphony problem probably due to loose PREA-PA ribbon.
Bad contour pot
LED3&LED4 usually on in overdrive
Contour pot C100K replaced with A100K and cut and crossedover traces
Marshall TSL100
reported fault same as switch problem on
JCM 2000 reported here
Marshall VS65R, 1998
the last time it was used was miked to a house pa as very low level
output.
By the time I powered it up just some low level
crackling whatever vol setting and no signal
throughput.
More a question of what solder points not o/c.
one pin of the bridge rectifier, input 1/4 inch
socket signal line, all the large W/W , 1 1W,
one axial cap.
Beefed up all the solder joints with added "washers"
of perforated zinc sheet - If i'd some copper
or brass wire mesh I'd have used that.
Remade all similar component jpoints.
Accutronics sprinline i/p 60R, o/p 220R
10 way connector, p10 = 8V
5 way , p4=-44V,p5 44V
preamp rails +/- 15.6V
T4 -43.4,-1.1,-44V
Marshall "Valvestate" VS65R, 1998
Reported as a nasty farty noise.
Yet again an amplifier that does not seem to know
that it will spend its working life on top of
a large speaker.
One tiny drape of hot-melt supposed to stop the
main ps caps waggling around - tied them together with
a cable tie , separated by a large nylon nut and
hot-melted into place and extra around bases. Beefed up
the solder points on the caps and W/W Rs with wire and extra solder.
Also the pre-amp caps treated similarly.
The pcb mount blade connectors will pull out
on removing the crimped wires to extact boards.
AC transformer supplies 33,0,33 / 300V / 13.6V
O/P devices badged Marshall T65 and its compliment T64A (curiously one suffixed A only),
Probably T64 = BDV64C, T65 = BDV65C
eg
Part Number = BDV65C Description = Darlington, Power Darlington
T65 NPN silicon darlington power transistor. Complementary epitaxial base
transistors in monolithic darlington circuit for audio output stages and
general amplifier and switching applications by Magnatec Inc
TIP31C, MJF122 (something like an oil film, only under the
central spine of the retaining clip that touched this Motorola device, don't
know what that means, original oil on sprung clip ?)
, 2x R33/5W + R33/7W and 2x 330 on preamp
also uses ECC83, 5201A, LM348, TL071, 072BDE
Marshall "Valvestate" VS65R, 1998
no reverb and then no audio
speaker 6.5R
broken wire on one tail of one coil
35R and 205R
mains transformer secondaries
13,225,30,0,30
For checking pa , conn1 , pin 6 or 7 .1V signal
uses 2x LM348, 74HC4316,,072,
4x 5201A mitsubishi, 4558,2x 180R
+/-12V reg, 071
pa 10R, 1W, 1.5K, 5x 0.33R, 4.7R .3W, TIP31C
Marshall Vintage Modern 2266,2007
No change of bad valve-type CH/R crackle, when tapping or pushing valves.
Putting bare plug into f/s so affected things but in retrospect was probablty
in white high gain mode and shorting of the socket changed mode to blue, unnoticed the LED or relay click.
Going to bad solder points on that socket but no use of the sw contacts.
Someone had been in there before and changed ECC83
V3 and V4
which function and tested fine. Impossible valve crackle
With bad noise pull V1 and noise carrieds on for 10 seconds so replaced V2
Much improved but still unnacceptable CH/R noise , pulling V1 and noise goes immediately , so changed V1
V1 and V2 are probably originals , at least 07 dates agree
V2 had a tested CH/R of 700K
marked VLVE 0066 and grey shields dated 02/07
V1 marginally acceptable (part of the valve sound) noise intrusion
VLVE 0067 and shiney shields, dated 04/07
with a tested CHR of 15M.
Now both measure 25M or better, driving heaters to 13V for a couple of
seconds and placed in my emergency- use pile of similar questionables
Is this just random failures or are there know bad batches listed
somewhere.?
From an amp retailer insider source BlackStar amps have been hit by complete
batches of amps with bad valves, did they take the same valve supplier they
were used to at Marshall?
In valve production is a routine final stage , over-driving the heaters to
push back the oxide coatings of the heaters , if they happen to be marginal
clearance.
I know this fudge , like for the 700K one above is only temporary in that it
will return after a few hundred hours of normal use, without vibration/abuse
op Tx 100.2R/102.5R
mains Tx 5R// Pu/Br 27.8R/34.4R to pins 1,2,3 & Be .9R to pins7,8
W/Y/Bk <.1R p4,6,29
Marshall 2266
Sometimes hum , sometimes buzz
Do musos know how shoddy their expensive kit is?
Another Marshall 2266 this time from 2009. The input guitar lead socket
soldering looks ok under x30 viewing but 3 of the 4 pins pull through the
solder with very little force, just that required to straighten the slight
bend placed there after insertion, the fourth pin pulled out with a bit more
force but still mush less than a proper traditional solder joint (that would
usually break the metal of the pin rather than break the solder joint).
Nasty grey appearance of where the solder blobs were and very little sign of
ever having been wetted. No mention of PbF on the overlays but solder
generally looks PbF and RoHS on the mains Tx.
N382 compliance? mark on the rear , coded speak for PbF ?
no pbf mention on overlays, RoHS on Tx and barcode label
Celestion 16R, SAD16 ACE, 7.5R in parallel
2x KT66 , VLVE 00039
prea
V1, 00066
V2,3,4 00055
Tugging on ip so was not too convincing but did produce a break in signal. Next time I
will try local heating as an upside down amp
valve can O rings as too thick to replace directly, remove the rings, place the cans and stretch
the rings over the cans and drrop into place.
Marshall VS100, 1998
"The amp suddenly started sounding very strange, playing
two separate frequencies when I played a couple of guitars through it,
before completely failing; it no longer makes any sound at all, other than a
mains hum. "
sp 7.8R
Tank 8DB2C1DR 33.7R / 215R out
broken 215R of tank
Cut one wire close to soldered pin, but break wwas the other end. Soldered some larger gauge
to the inner end to resolder and removed a turn of the outer end to solder back
mains Tx or-or 9.7R// Bn-Bn 4.7/Be-Be 9.7/r-r 0.6R
pull out both parts of the 3 PA snap rivets on the underside of chassis
Beware of bending the free to move and short terminations at the mains Tx, run a line of
hotmelt along them to lock together
Broken solder joint at a mains cap
Figure of 8 cable tie with plastic spacer in the middle , hotmelted together
before soldering
Marshall VS230 , 1996
Bad input socket
Also broken stem to the mains sw , push/push
No exact replacement, pcb mount made from 2 small eyed crimps, minus plastic.
Barrel cut down and pin of .15 inch header crimped into each. Eyes screwed to the sw body
and the pins soldered to the board , after wiring sw tags to the pcb pads.
Beware of losing the small function sw caps and breaking the solder joints to the
small electros at the board edge as only just enough jostle room to wangle prea pcb
out of the chasis , remove pot bushes with PreA pcb angled up then
rotate until under the PA pcb and slide a bit to release.
Amp will oscillate with no tasnl connected so short the red phono connector
sp 3.9R each, 4R specs
Spire nuts needed tightening at bends
Marshall , 8020, Valvestate 20, 1994
Kept in a garage. QC label inside Rita
Bad pots, bad input, bad phones socket bypass sw
fibre washer on each 1/4 inch so
tank 32/194R
Bad mains switch contacts
Comes apart quite easily , after banding back the wrap around bracing, MORS
molded under it. Otherwise APR France , IT 4100200
swivel latch to the A2 side with sw off position
Output started clipping at 10V ac over 8R which is probably reasonable for
16-0-16V ac and +/-18.5V dc
With no throughput , output heatsink is cool
Simulating a guitar pickup.
Find a 48 volt coil relay.
The one I use is 3.6K and 5.6H. If you've no tuning fork to twang close to it
then a set of steel feeler gauges. Ranging from 6 to 10 thou for bass notes
to 4 thou pinched close to the tip for high notes.
Matrix SR 4000 Guitar tuner
Nothing after being dropped.
All or most LEDs come on and stay on until switched off.
Replaced the 10M crystal.
Matrix SR 4000 auto chromatic guitar tuner, 1993?
Owner had connected an external 9V ps reversed
and knocked out the 78L05 as no reverse protection.
Replaced V Reg and cut trace to switch to put
a small 150mA diode in line
I was intrigued by another 3 pin TO92 device marked
8054
HN
3C31
Presumably working order - just wondered what it did.
Probably 8054HN not 8054 datecode , by Seiko,
activation voltage 3.8V to 4.2V, battery monitor.
One line is connected to INVERSE READ of the 80C51 micro
, I didn't trace any other lines.
Seems odd having this sophistication to hold
the micro from erroneous but not fatal operation
but no diode protection against battery or ext ps reversal,
especially in a product destined for musos.
MBOX MBOX
Told intermittant output so assumed mechanical socket failure. USB powered
SMD digital mixer thingy. Everything about this looks suspect except the
quality of assembly which is fine for China made, 2004
Make MBOX, model MBOX
Googling the "tick" compliance number "ACN 069 650 120" produces zilch.
Under a magnifier chippery such as Fairchild, TI, Philips , but under x30
they are blotchy printed bogus mock logos of F, the Texas state and
sonogram logo of Philips
and just numbers not likes of ABnnnn type numbers.
Without pc drivers etc I doubt this one is going anywhere , but just in case
anyone knows of a stock fault producing a hash output with no hint of signal
throughput.
with USB connected but no active pc. Hash on both channels of headphone
monitoring, cycling through on about 1.1 sec period. Worse when phantom is
on so maybe something with the 5 to 48V generator. Will try a few IC numbers
to check DC rails, check ESR of caps and disable unused 48V supply is about
as far as I will go.
XLR mic connections traced via 6.2K droppers back to
the rectifier diode of the buck converter. Looks as though the output is
gated rather than converter switched on and off for phantom. Will try
locating data on this dodgey looking labelled soic and cut its supply anyway
and hope it is not monitored by anything
There are threads out there on MBOX noise problems and caps.
Putting 2,000uF,10V across the USB supply seems to near enough cure it, is
that permissable, wrt USB spcifications? nonly a measly 10uF or so there as
far as I can see.
There are 4 LDO regs MIC5205B, topmarked LBAA, 3 hold their outputs but one
varies 30mV timed with the hash variation, Putting the cap there makes a
vast improvement but not quite up to the main supply smoothing. Will try
tracing all caps to that reg and replace them.
"417" IC on
3.1,3.1,3.2,0,0,0,1,1.2V
AK 43 93VF (U10) DAC pin 2 approx 7V pulse
Faux Philips 74HC08 and 74HC4094 on front panel,
transpired problems were numerous bad solder joints on the front
panel pots and headers. Noise diue to long USB lead and poor ground used
McGregor Raider , Bi-Amp bass amp, 1983
Farty noises and cuts out
Farty propbably from loose crimp to mains switch.
loose Brightness conn
poor phones T and Ring bypass sw
bad Hi out tip bypass sw
replaced all 1/4 inch so
Tx 15.5R// .9R 30-0-30
2x 6A fuses
3x LM348J, CA3094E
2SK133, 2SJ50, slack TO3 nuts
4x1K, 10R
speaker McKenzie Professional Series 4R GP15, measured 3.1R
To release grill sub frame 4 woodsc in corners
Sp o/p via phones bypass sw. Most 1/4 so are tagged but crudely used as pcb soldered
directly.
BC212, 2N5401 (marked TIP32C on overlay) BC182, BC182
30V ac on fuses
+/-18V secondary rails
no load TO3 .15,-.12,40V
-.4,-.12,-40
TO92
0, -17.6,.17
49.5,.15, 38.8
-.07, 38.8,-.7
-.25,39.5,-.87
Returned a year later after falling off a truck. Tx bent the front panel and the phones so broke
away from the pcb. Wired in inverted rather than relying on the contact solderings
Meridian KA-1510M, 2003, Korea
Cleanly cuts out totally after 10 min of use, and power LED flicjers
Phono and ext sp so will cut out amp, but plenty of spring contact
Speaker 6,5R stable
ext sp in series with int sp so no o/p on that with int disconnected
LED flicker solder problems at LED and nearby zener.
3x 100R 5W plus 1x 180R oddly
Bad solder on the 5W, tie together with silicone sleeving around and through tied off
PA screw loose so lacquer
Lower PREA pcb tip up to remove
B63?K (631?), D600K, 3x 072DE, 3x 072CN
Tank in 16R, 2.3K out
upper PREA
2x 4R7, 47R, 4x 072DE
PA 2x B817, 2x D1047
A1011, C2344,D600,2x D669, 2x B649
4x 0R3 5W, 2x 220R, 10K 3W, 4x 560R
Tx 9.5//0.9R
PA with 8R load and its input disconnected
TOP66 -.57V, -35.5V, 0 // .46,35.5,0
TO126 and 220 end to middle
0,-34.5, bridged // 0,-1.1,-34.5
-.57, -35.5, -1.1
-.53, 1.1,-1.1
.46, 35.5
34.1,8.2, 34.8 // 34.1, 1.0, 34.8
fit tank wires below upper prea
Test o/p with 8R load , 10mV 400 Hz in all mid controls
High .44 o/p , low .3V ac
Mic 2 1.2V ac
Left .13V , Rt .06V ac
Mesa Boogie Nomad 55, 30Kg
One output bottle dropped out of socket,
long term no reverb and problem pots and poor ch2 and ch3 , ch1 ok
input grounded at chassis, scrape back enamelling inside
tank accutronics 9bb2a1b 24R, o/c but repaired at 216R
Soldering iron , melt the glue on the hook anchors to the springs.
Ease back and tape all 3 together .
Release 2 suspension springs
32 to 35mm .5mm grind wheel cut off brass rivets and release brass clamp.
Mark diagonal line on soft iron laminations to keep the order when loose.
Break in wire was at the solder point to a pin , solder some fine tinned wire
as a bridge and hot melt glue in place .
Microphonics tapping anywhere on pcb in ch2 or ch3 but ch 1 ok , perhaps something to do
with both halves of V1 //ed in ch1 mode.
Swapped V1 with gains of 1.7,1.7 with V5 of 2.5,2.2 and microphonics went.
Doubled up star washers on all pots for spacing purposes.
Knobs all grub screw type
Mesa Boogie V Twin , 1997
This preamp must have been used in heavy rain, or something like , with the
previous owner. Had to drill out one of the casing screws to get inside.
Present owner has not had problems for the couple of years in his hands.
Vibration of drilling seemed to cure the fault so replaced internals
showing water staining
Working order , after vibrating , and could not reintroduce the problem,
but reported as a mains hum,
no output signal , but functioning LEDs.
Valves check out on tester fine, no change in any hum swapping them around. No
problems on any switches, pots or sockets. Soldering looks fine, No noise
on the HT line. Note insulated washer on power inlet
socket and beware of bending the red LED on refitting of case.
Worn legends are
Bypass, Clean, Blues, Solo
Gain,Bass, Middle, Treble, Presence
Monitoring on phones output some mains buzz at most
on minimum of gain pot and least on maximum. No effect on buzz , altering
the other pots, was due to having amp out of its case.
It transpired owner had used a 12V DC supply when the proper 12V
ac unit had cracked at lead outlet. Mesa transformer 1.5R / 250R 12V, 1A.
Beefed up with a halved
plastic knob glued around, made good wiring, and over a pair
cable ties. DC will power the SS and control but 12V ac needed
for the internal step up transformer for valves HT
Mesa Boogie V twin amp foot pedal , 1998
The bypass and solo LED are just where someone's thumb
would go when picking up the unit or a misplaced foot.
Ten yearold plastic bexel and glue around LED fails
and gets pushed inside.
Silver finish brass screw cup/eyelet from ironmongery.
Use the wrong way up. With a punch knock the
raised bit around the hole, flat. Grind
open the hole to take a standard LED bezel.
Instead of the ring at rear use a cable tie and
glue all together on rear.
The cup spreads any thumb / foot loading.
The bypass mode only works in normal foot pedal fashion
with "to guitar amp" output.
Uses 7812, 7812, 7805
2x 4N33, 74HC04, 4x 072, LM386 2x vactrol LED/LDR
Step up transformer measures in circuit 28.5 and 4000 ohm
With first 12AX7 in place and vacant second socket DC measured to case
243,0,0,14.5,0,243,0,0,0
second in place and first empty
254,248,0,14.4,0,248,0,0,0
With both valves in place and DC at the 4 rectifier diodes
236,95,102V
Confusingly, unless not original knobs, they go on
180 degrees from the natural flat positions.
Mesa Boogie V twin amp foot pedal , 1998
Bad power inlet socket.
Flimsey piece of deformed plastic under the
swaged surround of the bush. Interfering with
the outer contact which is then gripped by the plastic
and no electrical contact after that.
Cut away this plastic plus deformed plastic edges of the
barrel that are close against this contact so it can move freely.
Beefed up by cutting back a piece of small cable tie,
recessed over the contact, to pad out a bit and hot-melted onto the pcb.
Then 2 small "O" rings over to increase the spring/holding action.
Also plastic problems with Mesa , the transformer for UK
use, has very week plastic "earth" pin.
Mesa Nomad 55 ,1999
Distortion on clean channel and intermittant level drop
with external signal in at the "return".
Failure in the trace line to one of the o/p
valve heaters, making and breaking.
Tested the valves , all ok, returned the next day and
one of the 12AX7 now snow capped and a neat ring around the
top of the glass envelope. Obviously due to the bed-spring gauge of spring
inside the can. 2Kg to halve the spring length, probably 2/3 compression in
use.
No point in replacing without changing all the springs or something. How to
reform a weak straight compression spring (easily available) to conical or
otherwise fit inside the can and the glass touching end be centrally
posistioned. ?
Secondly there is no dedent to stop the cans rotating other than use of
heavy springs - catch 22. What to do, retrofit, without taking the amp apart
to get to the inside of the chassis. So far I've discovered a working , but
not elegant solution. One of those brass-eyelet hand pincer/dies pushing the
die pin outwards to deform a pip in the aluminium, outwards, 1/4 way round
so it locates in one of the 2 chassis cutaways. Needs some rubber padding on
the outside so the other anvil half does not excessively damage that local
area. Any other solutions anyone else has found, particularly forming or
re-forming spring metal to something like conical My attempts are very
wonky.
This is a work-around for the springs. May have gone too far the other way
200gm rather than 2Kg. Expanded aluminium mesh (for continued ventillation
through the central hole in the can) cut to a square to squash inside the
can. Straught 12mm diameter compression spring. One end , the last 2mm ,
bend to point axially. Thread that end through a suitable hole inthe mesh
and push around for a near circle and feed back through the mesh with the
return poking through the adjascent hole. Curl back the corners of the mesh
enough to push into the can. Use a din connector cover to go over the spring
and push the mesh into the can. Then with din cover in place , use a
screwdriver to push the mesh down to wedge into the can top. The spring then
stays centrally and axially located .
The eyelet pliers fudge works quite well for dedenting the cans, combined
with the existing "O" ring antivibration ring.
Uses 56K, 68R, 2x470R
220R, 5W
Bad pot marked 593739 0129 , 1M log, probably due to too
much grease and migrating onto the pot track.
Midiman, M-Audio Omni i/o audio processor for A/D, 2000
Owner plugged in a new microphone that blew one channel.
Pre-amp uses a Burr Brown INA103 very low noise instrumentation op-amp.
In this M-Audio Omni i/o preamp and an outline design application in the
Burr Brown book show much the same circuitry the 48Volt phantom
supply to the mike is protected by 6.8K limiter resistors.
But to block the 48V DC to the op-amp there is a 10uF/100V electrolytic in
each line directly to the inv & non-inv i/p of the op-amp and only 2K to ground.
If , as seems in this case, a balanced line microphone with a short to
ground is connected to such a system
then the +48V / 0V across the elecrolytic will instaneously go to 0V
/ -48V with -48V
directly connected to the op-amp i/p powered from +-15V rails and according
to the databook can be taken to only +-12V.
Added 2 back to back 6V,1W zeners plus 10R to ground for
each of the 2 inputs to each expensive IC.
For the blown one replaced with an OP27 very low noise opamp
glued over a 16 turned pin socket , with mods,
first original pin number and second is OP27
1 to 3 via 68R
7 to 3 via 3K
8 to 4
9 to 7
10 to 6
also on original (turned pin socket) only
6 to 16
10 to 15 via 3K
13 to 14 via 56R
Functional replacement for the INA103KP including the -20dB cut.
Unit also used NJM4560 SIP amps and a 7555 for 48V generation.
J2 DC voltages with all pots set low
1.6,1.6,0,0,0,0,15,0,-15,0,0,0,-13
lines 2 and 3 are the signal lines for the amplified 2 XLR inputs
Miditemp MP88 , 1994
MIOC processor
Just light on the display, no info
9R between +rail ? and display light anode, K to gnd
D connector
1 &2 Y & Gy
4 Gn (broken wire)
5 Blue + Bn
6 Pk
7 W
Internal header in R/C, no marking on overlay
1 Gnd Y + Gy
2 Gn
3 W
4 Pk
5 Bn + Blue
Green wire broken. Replaced D con and added cable protector at
cover and added similar under cable clamp on R/C.
Monaxor MPX 3400E , 2005 ? digital echo mixer
Breaking output connector problem
A lot of solder points on the rear board were suspect
although not seemingli dropped.uses 7805m the spring is for
earth connection to front panel
MM Electronics MP175 16 channel mixer
One master output board bad, output only for first quarter of slider except momentary
at sw off , if slider is advanced beyond 1/4.
IC3 p6 of good board .45V dc
bad p6 , 1.2V
IC2 good p6 0V
bad p6 .45V
.65V on bad slider pot
All Ds and Qs DVM diode test ok
replaced IC3 but same
Slice through bus wires as sharply diagonally as possible so some overlap when
resoldering. I tried removing a rotary pot with board in place and slackening neighbouring
pots but overall easier removing a board to work on.
-4/3V on p2 of middle 741
+12V orange wire to negative of meter
from left meter to right meter bad solder on a wire link
+/-14 main rails
bus +,*.*.**, -, 0
r ch board wiring colours
Y,P+Gn, W, P +Gn,G,-,0
l ch colours
O, bus all 7, Bk,P+Bk, Pk, P+Bk, Bn, Gn , O
L ch middle IC had a later IT 741 , all others RCA
As p6 of this on R ch bad replaced the same IC on the R ch
line 1 is +
left is bus line 2
right is bus line 3
for phones monitoring line 4 is foldback R
line 5 foldback L
lack of output on one chanel , testing with a single input line , if multiple then would
have masked this, broken ground wire at ch input
Motu 828 Mk2 FW, digital processor, 2004
Sizzle like noise sometimes and then no function
15,000uF 10V 105 deg Ccap had vented and medical clinic smell, 4x 0.47R , 2 charred and had
risen in value to about 1R.
220R, 2x 5.2R (?), 6K8
L<1117, 7906, BB 103FA-5
3 mains Tx measured at IEC 160R
1/ sec 308 365
3/ .9 +.9, 1.2R across
3/ 1.4R across outer terminals
reinforce front panel to pcb with hotmelt glue before removing from chisis
or handling. The underside screws just reinforce the pillars so leave in place.
Low mains , display only of opening logo and vertical bargraph under SPDIF.
9.6V input to BB and so 9.6V on 10V rated cap, replaced with 16V but 10,000uF
105 deg C. Maybe inadequate ventilation as along 19 inch width and 1U height.
Added 10mm hole over the 2 large Tx and over this cap to get some convection, noting the webbing
to the die cast case and height of C and 2x Tx blocking off any thru ventillation where it is needed
header 2 as powered up state
5V ?,3.2V, 1.6, 0,2.3, 3.7,10.6, 0
rear header
2.2,2.4, 0,2.4,2.4,0,0,0
.28,0,.45
0,-3.2/8x 3.5V/3.3, 5,0
-10.6V on 8906 HS
49V on LM317 HS
3.25V on LM1117 HS
Front display needed easing into case slot on reassembly
Nady TD 1, guitar tube distortion effect pedal, 2004
Anyone else been here before ?
End of line , being sold without the power adaptor, presumably ran out
before the units sold out.
Contains a valve so the wall-wart supply is 9-0-9 V ac and 3 wire for an
internal step up transformer ( presumably , not looked inside yet), no great
problem there to do that.
But the connector on the unit is a 3 pin locking din, like CB mike
connector, but the pin spacing is non standard, 5.5mm between pins rather
than 5 mm.
Normally, in such
situations, I would change both parts of the connector to something standard
or just wire in through a gland.
Had to get inside to check the wiring as cold testing not consistent with a
transformer and no confirmation anywhere other than anecdotal/verbally that
the supply is 9-0-9 ac, centre ground.
That feeds a bridge R and then 7806 and 7906, 4 4580D smd opamps and a
12AX7.
Where is the HT supply ? caps are 10V,16V or 50V, input socket contains 2
crudely epoxied small unlabeleed black lumps with 6 pins
one has pin-pin resistance readings of 13K,360R and 0.1R or less
the other 18K,360,720, 0.1R or less
So perhaps transformers there, but smps combined with input amp in a can? ?.
A smd 8pin device marked AD 741 and OP 275G and a few TO92 transistors but
nothing SMPS looking inside.
Then the final test, the wiring to the valve. Whether plugs are in or out of
the 1/4 inch sockets the anodes of the genuine looking , but no label valve,
are connected to one end of the heater chain. No viewing hole to let the
owner see the presence of a glowing valve for the psychological effect of
the valve sound. Only + an - 6V to the valve to power the heater, no HT.
No larger voltages on the valve than the -6 volt and +6 volt to the heaters
and unit worked perfectly normally when tested .
Incidently note the various casing screw lengths, on disassembly as the long
ones would touch the pcb if replaced wrongly
Don't forget to add the 2 large spacer rings to the footswitch
before fitting the board in the box.
NJD Spectre theatre stage light, 2003 date
Gives fully variable, total spectrum, floodlight output under remote control.
Or it would but nothing now. Full of dust and fluff in the control area and
a long term heat damaged , so presumably dramatically raised ohmage
resistor. First thing to beware is disconnect the lead to
the NTC thermistor for heat sensing it is very weak
at the epoxy glue point. IMO this should be
in a PTC circuit as the controller will work with it
disconnected. Also there should perhaps be an overall
thermal cutout connected to the lanmp mounting
plate. This NTC according to the schematic was 20K cold
but I measured at 25K. Fan would cut in at about 4K
but much higher than the design 50 degree C so added
12K in series. As R6 is very close to the lamp
mounting plate I suspect the whole unit had been
overheating before the fan was cutting in.
Schematic available on request via email to njd.co.uk, not the same as
this model.
The bands are only discoloured , 5 percent and 2W
size. Coluur bands look exactly like 100 ohm but
measuring gives 47K , the same as the R6 value in the
schematic. Replaced with 2 100K , 2W in parallel
surrounded with ceramic beads to allow positioning out
of the way of transformer and metal work.
The opto is 4 pin P620 Toshiba TLP620 , current going through
back to back parallel LEDs of 50mA rating with transistor receiver, presumably
passing phase info to the PIC controller.
LED side of the opto seems ok at 1V diode-test drop either way.
The fan would come on and the lamps only control was
on or off via the remote hand control and half
brightness setting. Bypassing the i/p side
of the mains side o/c then full lamp brightness
only. I convinced myself
that despite the LED going from red to "orange" signifying
correct control pulses being received I thought there
was a problem with the Tr/rec SN75176BP , i now know
unit will work with a SN75176A. Easy to flip the
DIP sw settings .
Seems to differ from the internet available operation
manual for the DIP Sw settings. For single remote
control then off/on/off .... , setting to that configuration
brought full control back. on/on off... or on/off ....
loses control function. The triac may that controls
the fan may have been malfunctioning so replaced
with a TO220 one
NJD SFC 1 , 2003 , lighting controller hand unit
no control
uses large PIC and SP483CS, data for which shows 0 and 5V pins
so connected 5V to the board.
Noticable corrossion on the PIC pins but not the socket.
Grubby 8 way FCC68 socket wires , cleaned and pulled back in case of loss
of contact. 0.5mm Cu wire bent to a loop and pushed around the 8 wires and
it and the return pulled back , the central pins reconfigured by using a hook against the
introduced Cu wire.
.25s continuous varing signal train so set on 10s
Colour codes only varying obviously on a scope in Fade,Chase and manual ranges and the isolated pulses in 4 "repeat"
blocks of 2 or 3 pulses changing as blocks 1,2&4 ; 1,3&4 etc
Beware of losing the black ferrules of the pot shafts
Another one packed up. Bad solder on one pin of th extal , not the problem.
Bad trace or solder under the RJ socket.
Speed pot fram is at 5V , anothe rreason no tto loose the plastic ferrules.
oV on one of th epins of the pot at the other end, for bench powering
Nord electric piano soft case
Rigid plastic tube handles around core webbing
but the plastic cracks at hand edges where the shear stress is.
Push a length of soft formulation
hot melt glue stick through the core of the webbing of each of the handles.
If comfortable with it heat up with hot air to meld into the webbing
and perhaps hot melt added to the breaks in the handle, but made to
take up a squat U shape rather than straight.
Norman NT100, 1970 amp
Severely worn track of the "middle" pot meant, except for
a few small positions, there was excessive hum through the amp.
Removed all pots and reconditioned. Added a heatsink to
the 3055 as seemed rather hot.
Uses 4 2N6254, 2N3055,ME8002 and BC18?C (184 ? )
Main board says Tuac TP 100W
Main ps 48,-48V
DC on smaller Trs and the 3055
3,0.8,0.2 / 34,3,2.3 / 37,2.3, 0.1
34V,43V on small electrolytics
0,48V across one W/W dropper .5,48 on the other
and 48,43 across the smallest W/W
Preamp supply was either 43V
Numark Matrix 2, CD DJ desk , 2003 ?
The central mixer separate.
Anyone happen to know where 2 fibre washers , as used on 1/4 inch jack
sockets, would have come from. They dropped on the bench , unnoticed. I
cannot see 2 being left over at assembly. The 2 sockets I had left in place
so not from there. No obvious place to put them. A fudge due to engineering
fixings alignment problem ?
Not a sheet metal work cock-up, the rear sub-chassis despite 1.5mm shorter than the
front so 2 fibre washers, for padding out, so as not to strain/split the
plastic outer case, is allowed for. Never did find where to put them
In for bad output RCA/phono socket but now in there, the soldering elsewhere
is terrible , not PbF probably just not enough solder, ring cracks emerging
on the ps board including a wire jumper joint. Bodes ill for the 2 CD units
Remove silver facia plate 4 sc topside, 4 sc under , 2 sc at top , lift up .
7805a, 7815a, 7915a
ps board wire link to 7915 bad solder, a caP bad and redid 1/4 so
bend VR away from caps while in there
2 top front sc at front leave in place but slack to allow the flopping inwards of the panel below, on
extraction and opposite at insertion of assembly into casing ,
insert rear first.
Did not survive for long, had to get back in there and do a more robust hack of the master out phono sockets.
Grind off the contacts and the body parts of the original phonos, also ball mill
for the
parts nearest the pcb. Open out the holes to take the screw
parts of 2 chassis type phono sockets. Wire the 2 ground tags together an dfix nuts. Swathe in loads of
hotmelt glue to hopefully fix to the remnant white plastic. The Black 2 hole escutcheon and the
metal plate under cannot be reused. Us ethe black as a guide for
posistioning the new sockets. To retain electrical isolation. Opened out the 2 holes in the steel
with a tapered reamer and fitted chanel type nylon grommet strio ,each end partly melted to
alow a tight turn for the ends. Replacements have tubular signal contacts, no tthe forks of the originals.
Did not think of it at the time but a solution is probably cut away fully the originals, fix insulated
chassis sockets to the steel frame and wire through to small line connector and socket added to the pcb,
nothing more than 3 pins of a turned pin IC socket perhaps
Ohm Solo SC60 , 1983
Speaker o/c and knocked out TIP tr, don't know
which came first but final straw for the speaker, actually
corrosion/work hardening inside solder point of the
tag terminal.
Remove front speaker surround by 3sc under and 2 large ones inside
Amp slides up and out after removing front 2 sc
Springline Accutronic 3106610, 670R/ 23R
65V ac
with 8R load, back line DC
-2.7,-16.3,-2.1
0,43,.4 / -43, 0,.42
-.5, -42,0
0.9,0,0.4
0,43, .4
With ampremoved in free air and plate laying vertically with thermometer
fixed on top edge
12 minutes to plateau at 23 deg C over ambient with 36mV in , 400Hz,
giving 9.46V over 8R and all pots half way and 2 RED LED lit
2x RCA2N6254
TIP42C, TIP41C, 2N3440, 4 x TL072,
4x .33R, 5x 4708R speaker, measured 6.7R when replacement
pigtails made up and removed dome to solder into existing .
Tr 24R//1.3R
Oktava Mk-012 microphones
Expensive Russian mics. Is there any pitfalls about getting inside the XLR barrels? eg threadlock on the obvious screws, twist the wrong way and some 70swg wire breaks or something like that?
One barrel has something acoustically , not electronically, loose sliding around inside and the other has a bad electrical connection of some sort
utube video makes it look easier than it is. 3 x screws screw inwards enough for top to clear the tube. Holes only enough to allow
entry of jeweller's driver, not to extract them and quite a bit
of force to push inwards at the mic insert end.
Now I've got inside may as well find some sort of info/equivalent for the 3BF1 and 3107E transistors. With blue electros like the Philips ones of 1960s, looks like 1960s inside but for the glass+polyester pcb
schematic on
http://taperssection.com/index.php?topic=141868.30
In one a loose screw , needs nail varnish on these screws.
The other one looks like a cracked die in a transistor from being dropped.
I'll have to go with these www refs
FET ABM7 = ( 3BF1?) = 2SK170BL
PNP Si marked 3107e = BC179AP
for the moment.
Then the usual conundrum as a matched pair of mics with 3 inserts each, will have to make the desicion of replacing with the same matching transistor replacement in the broken one only or both mic stems
Probably a mechanical problem. The insert end core is not firmly held transverse to the pcb, and so poor contact between the mic central pin and the sprung pip contact in that core disc. At least plenty of space in that area to add a plastic brace (cut down nylon pcb standoff) to farther back along the track side of the pcb . mic1 loose sc inside, mic2 sometimes bad motorboating noise, otherwise worked as normal
30V ps and 2x6K8 droppers
mic1 no mic insert G 0V, D17.1V , S 13.6V ; B4.1V, E 4.7V
mic2 no mic, G0 , D17.3V, S 13.5V ; B4.1V , E 4.7V
Testing with mic insert in each gave good output after reassembling
covers. mic2 sometimes bad open-loop oscillation, motorboating.
omni-direction insert measured 1KHz 60 to 90pF.
With mic1 and omni insert ,30V ps and 25.6V on both 6K8
G .23V, D17.1V, S13.6V
Replaced mic2 FET with 2N2966, as 4 pin , but a switcher
30V and 25.3V
G 0.24V, D 16.4V, S 14.1V
upping supply to 48V, then 40.3V on 6K8
G .39V, D 26.2V, S 22.0V
Mic testing / poor-man's anachoic chamber
I've had to replace a FET in one of a once matched pair of phantom powered mics. We're not too worried about any difference in gain as that can be balanced off on the mixer. But is there more noise compared to its fellow?
The only mixer I have around with 48V and balanced feed mic inputs has a fan in it. However I wrap the mics I hear/measure the fan noise. Long lead and I get mains hash/hum pick up. Looks as though I'll have to go inside the mixer and temporarily cut the fan. Any other ideas or what to place the mics in that is as acoustically dead/mechanically non-transmissive ,that I can conveniently find laying around
I tried replacing insert with a cap and was picking up a bit of mains hum, I'll try again with some shielding over the 100pF cap, I'll even try some mu-metal.
I was wondering how much mechanical noise came up through the mic cable, I'll try clamping some lead sheet around its middle, might deaden any through vibration
Laid the mixer on thick low-density rubber slabs over concrete floor and a sleeping bag loosely wrapped over the fan outlet. mic pushed into a large block of foam rubber and wrapped inside another sleeping bag.
Had to wait until no cars moving within 100 yards and no planes, including what I didn't expect , them taxiing at the airport 3 miles away.
In simplistic DVM RMS voltage terms the replacement FET one was 19% lower noise minimum for the same amp gain settings than the original.
Setting each over a speaker with a more normal sound level, the old one had 22% more gain for the same amp settings.
Hopefully that means no extra noise intrusion with the replacement FET and just balancing off the gains at the desk. The FET was not made for low noise purposes but was 4 pin in a shielded metal can. I'll leave at that rather than move onto frequency curve plots and let the owner see what he makes of them in normal studio use.
Orange AD30TC, 2007 to 2009 probably
Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is failed
both sides, 0 percent output . Inspecting the fuse it has failed at an end ,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast make/break
intermittant action of the fuse wire at an end , would that knock out an RR
valve? What in general happens in the failure of RRs ? I've only ever seen
75 percent , same as new, or 0 percent "goodness" at prescribed current
settings of the Avo valve tester.
As for sag R I tried 50R and 100R and a couple of GZ34 on Avo CT160 tester
set for 120mA per anode.
each GZ34 showed the usual 75 percent "goodness" .
4007s and 100R showed 70 percent
4007s and 50R, 10W showed 75 percent
It seems the mains fuse I have here was not necessarily the original one.
Someone looked at the amp and replaced the fuse, probably with this probably
previously mechanically broken one (knocked about in a toolbopx). The
original may not have failed but assumed to have fused and so just rectifier
failure.
Could generator brownout or spikes or something weaken a valve rectifier so
it is ok while warm but gives up the ghost on the next powerup from cold?
Replaced with plug-in 4x4007 and 50R 10W so owner could replace with thermionic
if he wished.
Remove black sc only from top face and one only under pcb under the mains Tx to remove main pcb,
remove 120/240V sw , disconnect IEC delatching the spades, remove fuse carrier and wires -
back nut round section to chassis not nut section
Replaced the 19 inch rack handles with nuts and bolts as too weak for carrying
amp , cab and speakers - too easy to use rather than purpose made large side handles.
Speakers 13.7R Celestion vintage 30 , 8R
Standbty sw is in return path to ground on ac side of the rectifier
With 108V mains , purple 240V, r-bk 2.2V, T-T 2.9V
From pcb Enumber E171525, the boards are made in Hong Kong, despite Union flag logo
on the overlay and "Made in England" on the chassis. I will assume No-Name
Chinese valves unless anyone knows any better, scraped off make and badged Orange.
Nasty metallic buzz like mains powered shaver/
engraver/ poodle clippers. Varying level of noise with amount of load.
Mains Tx central bar of an outer "E" lamination loose. Simple enough to deal
with once you know the cause. Remove the matching "I" to drible lacquer both
sides. The wiring bobbin is loose within the iron laminations block, so
plenty of space to allow a lamination to break away. Will also push some
silicone rubber sheet in there to avoid re-occurance hopefully.
The owner had lived with the "shaver" noise for months,but had gradually got
worse. Masked by the demand effect, no music - light buzz, high music
volume - loud buzz.
Absolutely quiet transformer now. Just hope the other end "E" does not play
up as that would require removing the Tx and its wiring from the chassis. It
is now tight up against the bobbin now so not too likely .
The other notorious Orange problem - intermittant loss of one channel,
whether by sw on front or footswitch.
Although they use latching 1/4 inch spade connectors, just because they will
not dislodge, does not necessarily mean they retain electrical connection.
Green heatshrink covered spade was the culprit
Bend outwards the EL84 retainer mounts to clear the glass.
Check the pcb pillars and screws are tight before reassembly
7mV 400Hz in , mid pots
ch1 1/06V over 8R
ch2 1.7V over 8R
Only 4 wood screws hold this amp into the cab so as cantilever action ,
beware of loosening screws and amp dropping out, no top mounted bolts.
Returned a year later as mains lamp went out and amp died once.
lamp is off the 6V heater line
Nothing specific found but crimp tags to mains sw a bit loose and also pcb heater tag crimps
Front panel ch1/ch2 sw inoperative , external
footsw use ok, due to bad rear footsw so sleeve sw contact
Orange Rocker 30, combo, 2006
All valve. Intermitant cutting out.
Incidentally are the solder pads gold plated before soldering ?
No mention of PbF but appearance & paper & indent test hints at PbF. Crimps
adequte, switch functions ok, all solder points look good (for PbF) x5
inspection /tugging, preamp valve bases pass needle test. Other than
resolder most likely suspects , any known problem with these amps?
Definitely PbF, resoldering the usual suspect points.
I realised I was using the wrong gauge of cut down sewing needle and 2 of
the preamp valve socket pins are highly suspect. Those glossy white ceramic
mounts with holes just bigger than the valve pins.
Coincidence or action of high V on springiness of the socket metal?
One valve base, pin 1 , the other pin 6 , both anodes so killing throughput
if connection fails.
Remove sticky foam and stow until reassembly.
Thick spacers on pots
1K,270,330,1k,150
47R over nat vol pot with relay unpowered
Disable 120V/240V sw for UK use
speaker 16R , 13.0R, DC
Diverse Devices,Southampton,England
Telephone number - the same number as it has been since 1988
but email is now the preferred method of contact so number deliberately not placed here.
I devote time each day to replying to emails.
(obscure/obsolete components,second hand test equipment,
schematics etc)
Postal: 66 Ivy Rd, St Denys, Southampton, Hampshire, England , SO17 2JN
There is no point in contacting me about any of the above, the
repair job may have been done 15 years ago .
I cannot clarify or enlarge on any of the above.
A reserve email account is diverse9(commercial at)fastmail.fm.
Please make emails plain text only , no more than 5KByte or 500 words.
Anyone sending larger texts or attachments such as digital signatures, pictures etc will have
them automatically deleted on the server. I will be totally unaware of this - sorry, again
blame the spammers.
More hints & tips and repair briefs on
homepage http://home.graffiti.net/diverse:graffiti.net/
