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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 , P to S 


Pearl Octaver compressor, 1984
Would switch from bypass to function but not 
return , without unpowering it and starting again to reset.
Replaced the MN4007UB with CD4007AE (happened to be at hand)
That one of similar age failed in a different inverter 
leaving symptom of latching LED on or off 
but no compressor function, just as well I'd 
desoldered the original and placed a turned pin socket there 
in that case failure of pin 9,10,11,12 inverter

Peavey IC/transistor cross-reference
http://www.slideshare.net/modestoguillen79/pv-semi-cross-ref-2009
beware there are some wrong or questionable references

Peavey 701R 7 channel mixer, 1990
loss of signal and bangs on one channel and 
occassional whistles and noises on the other.
Remove all fixings on rear except the earth bond point 
to remove rear panel. The XLR surrounds 
come away with the panel. Temporarily 
replace the mains lead to facilitate.
Remove springline 59R and 193R
mains transformer is 237R but as 25H 
cannot measure with autoranging Fluke DVM
All 3 front panel switches were dodgey, as 
welded cases had to be replaced. Difficult 
as non standard DPDT though 2 could be just SPDT 
shallow format. Luckily had some ex-kit 
small ganged slide switch blocks with separate 
locking actions. Footprint different 
but could be bent to suit the pcb holes. 
Before removing mark cross lines on the pcb 
by lining up a pair of steel rules on either side 
of the knobs as they must locate with the front panel holes.
And used same button shaft size.
Rotated the interboard connector arrays 
and resoldered all the socket and pin sections just in case.
Wrong shape of solder pins for the holes so some of 
them looked to have had cracked rings around the holes 
and insufficient solder, so next time do this 
first instead of replacing switches first.
4.6 mm splined shaft, 8.9mm AF bushnuts pots. 
main supply interconnect
0,0,-24,24,-15.8,15.3,0,0
nothing much on the others
One pot shaft sheared and repaired as per tips 
as non standard pots and replacement knob 
as per tips. With the back panel removed make 
a ground connection from an input socket to the front panel.

Peavey 5150 , 2003 USA made
This is an export model for 240V/220V areas, no 110V option.
Demounted the switch and remounted with a cover over the 220V 
option as it was in 220V setting as received in 240V area
The mains lead has a German integral plug( 2 round pins and a removed earth
pin but an exposed earthing point) on the lead with a German? socket to UK
plug adaptor.
This adaptor is presumably used on other equipment for this purpose.
Despite BS kite mark etc it is a very vague connection between the earth
point of the German plug and the UK earth pin. In this one there is no earth
bonding as it is so easy to dislodge the plug relative to the adaptor and
losing earth bond , thin spring connection.
Adaptor is SCP3 made by PowerConnections , Harlow, England.
Needs totally removing German plug and adaptor and fixing a UK plug on the
lead.
Not a screw in earth pin but a push-in pin from a
socket for earth
Plug type number? TA-6P , and country ? designations
D, S, Fl/Fi?,öve,N
To get inside, leave handle on top , remove both pairs 
of side screws to remove the front and 4 screws at rear 
to remove the back and then remove the feet to slide the 
chassis out,
One 6L6 had a screen leakage problem , not 
obvious doing cold tests but after eventually 
getting a tester zero prior to mA/V test, 
neg grid volts of -4V or so varying to -7V 
should have been -18V. While still hot 
from this then showed leakage on the screen test.
2A HT fuse was "soft" blown ie most of filament 
remaining and no black staining. 

Peavey Bandit 65, 1983
Bad input socket.
Weakened metal on the U of these open sockets.
Opened out the U so the V tip of the contact is in line with 
the V tip of a plug.
Tied tight a cable tie around the curved section to reinforce, and 
the same on the other socket. No point in replacing 
these as modern ones will  be weaker anyway.
Reconditioned 2 of the crackly single pots, 
no need to de-solder.
Uses 2x SJ6392, only 4558, Motorola 339 and 326
3x 0.33R, 2x 500 , 0.22 and 220K (may have been 
4.2K which was how I read it , probably backwards, 
part of coating was missing).
Beware the speaker line isn't touching the casing 
at the exit hole on re-assembly

Peavey Bandit 112, 1994
All pots bad
10KB,"514",50KB,"515",10KB,1MD,10KA,"518"=10KA,"518"

tank 52R/193R
Peavey chip ceramic cap labelling of 1990
The schamatic of this PV amp out there is for 2000, this 1994 version quite different. All the CC caps are small mustard colour epoxy covered small cylinders. Labelled with likes of 473 or 104 presumably for 47nF or 100nF but what about marks of 424 and 419?. Or are these the week/year date marks and the 3letter codes such as KNO and RSC are the value markings?
2 of these are physically broken, the wire ends broken at the solder slab. One labeled 473 measures 57nF and one marked 424 measures near enough 100nF. Vibration failure , inside Bandit 112 combo,preamp section with no stress telltales anywhere ? 
Looking properly under x30 mag
The 2 broken ones are marked
R5I
473
and
KDQ
424 

Peavey Bandit 112, 19Kg
Handle broke and then dropped amp and no go.
Broken handle because probably just one nut tightened against 
wood and so slackened and fell off. Needs at least 
nylock nuts.
Tended to the usual suspects, fuse-holders, 
big components and in this case the over-temp switch.
Returned to normal service.
The under slung mains transformer, probably a mod 
for UK as 240V only primary failed the earth bond test.
The mounting screws although not so loose to fall off 
with transformer following, they were loose enough 
to isolate from the rest of the chassis. Mains 
primary for UK about 11 ohms
PA board only looked at, uses 
70483100, 70473100, 5331 and another 
covered in spot paint , presumably 5332 
3x 4560
W/W Rs 4x 0.33, 2x150,5R6, 2x 2K
MO 2x 22, 2x2K7, 6K8

Peavey Basic 112,1997
Cuts out at random times
Speaker mod.054 6.2R
mains tr 37 // 1.5
70483100, 70473100
4x 250R, 2x.33, 22,150
3x BA4560,7041,3080
motorola 5331,5322
Fractured speaker pigtail at the solder joint.

Peavey Black Widow speaker rebuild, 1979
Not made for the UK climate, stored in a (normal for UK) damp garage for 3
years, came out making nasty "amp clipping" noise.
I don't know how general this is for different manufacturers but for
unsticking the contact adhesive of the original cone and spider skirt.
I tried hot-air gun , oven cleaner and acetone but the one that worked on
the one I did this week was petrol. Some strips of tissue paper soaked in
petrol and covered with some circular strips of plastic and leaving for half
an hour to soften the glue
Now it is totally apart, small bits of aluminium oxide in the voice coil
slot were causing the distortion along with loose skirt biased to one still
retained side. 15 inch size with aluminium basket.
The voice coil is in perfect condition and no imperfections to the cone
despite 30 years old.
Prior to me getting to look the owner had removed the 3 magnet retaining
bolts and removed some perished foam filter from inside under the mesh cover
and squirted in WD40.
The white oxide formations had burst the glued skirt off , about 80 percent
of its rim, and the same for the cone rim (after removing the periphery
bolts) and nothing much holding on the remainder, easy to prize off.
masked off the central voice coil slot area before
abraiding back the lands to take contact adhesive to replace the skirt and
cone. Then air blast and run thick plastic around the slot to clear any
crud. The magnet does not seem to be corroded, shiney, no obvious rust
spots.
The 0.08mm thick aluminium dome must have been press-formed 
or by metal spinning with a cylinder
extension to the dome and the cylinder section is glued to the inside of the
VC former. So had to cut around the dome to remove and hope the
final gluing-back holds up against the air pumping process.
I just used 4 ball point pens in the rim 
mount holes for rough alignment and some clothes pegs to give a bit more
clearance gap for laying down the glue. Removed them prior to dropping the
cone in case they gave some bias.
I'm just wondering how much the "monocoq" construction of the Ali dome plus
cylinder gives circular stiffness/precision, that my cutting it has
destroyed. 
Voice coil 47 turns counted but doubled up ? , 
not checked or width, circumference unfortunately.
3.2 ohms , tested with 5V ac of 
10 Hz into 4 ohms with speaker not in the cabinet.

Peavey Classic 2009
Bathtub curve failure or something more?
A birthday present of a new set of valves in a 2009 PV classic 30 and after
a few weeks of use , copious magic smoke and then nothing.
V7 has a near to short varies [cold] 3 to 6 ohms or so  cathode to G3, p3 ? to
p9 of EL84 mechanical failure inside, burning out the HT1 to HT2 dropper
R58, 400R. Anything that could externally precipitate such failure to check,
before a new valve/s ?
One side of R58, 101R to gnd, R53 2.7R to gnd
Remove V7 and goes to megohms
Remove tank and 2xP clips
I have to replace the dropper first, ridiculous mechanical design of 3 "wrap
around" boards with
something like 2 sets of 27 short link single filament conductors.
Presumably copper and with age and work hardening , what is the probability
of one of those links failing in the unwrapping/working on/ rewrapping
process, then the probabiliy of another such link failing in sorting out the
first failure. Replacement dropper will be wrapped around the stand off
pillars, I think.
P3-P9approx 3R.
SovtekEL84M
So what is the metal of those 50 or so short curved links, that you have to
bend all of them to unwrap the boards? something specially formulated that
does not age and work harden? I doubt it , probably deliberately designed
like that to make repair as awkward as possible. Could easily have been
soldered eyelets on one edge of  each run.
Perhaps you have never come across ribbon connectors that fail at a solder
point , only because you've had to flex the ribbon to gain access . Or
moving the discrete wires to the wire-wrap terminal boards of 60s kit?
Anyway heatsinked (meaning artery forceps clamped around while soldering) the pcb ends of the pillars and 2x1K 2W plus 2K2 2W in
there now, could not find a 400R,5W of the required dimensions to otherwise
go in the available space
For a valve/tube amp why does it say minimum load 30 ohm on the back or is
minimum actually maximum in USA useage?
It is a regular complaint by owners of these amps. May be not so obvious
when they are used in 60Hz countries, 50Hz here. The next time I came across
one I might explore with small pieces of mu-metal around the coils in the
tank, and put a scope on the thing. Reading around mu-metal it seems that to
restore its invisibility cloak effect then you just need a hydrogen furnace
to re-anneal, I'll knock one up from my pile of scrap
Returned with R58 oc again. This time no low ohm path to gnd. 
R58 to R43 and R44 ok as are all white W/W
V5 tested S/R of 0 , on CT160 before applying heater voltage, p2-p9 short, G1-G2
Refitting the 3 pcb assembly. 
Place the rear pcb in and out of the way towards the edge. 
Introduce the 3 boards and sc the valve base section to chasis. Push the 
rear pcb into the space between the 3 boards and wangle into the holes 
in the rear

Peavey Classic 
o/p Tx 126+96// .9R
Mains Tx , Yellow secondary wires nearest Tx
30V ac over 4 in series EL34 heaters , initially , drops on load
Running the amp on 2 only EL34s not possible
On the 3x ECC83 36V DC initially , dropping on load
-13V bias on interboard loops, 9 and 11 from mains Tx end. 
As PbF took the amp apart and redid bias solder points

Peavey CS800S, 1997
Loss of one ch
Bad solder at 1/4 inch and XLR weak/bad internal switch contacts.
Bad solder at power outputs
Bad anchor screws for the IEC replaced with nuts and bolts and 
bad solder on pcb behind.
To remove ps remove screws under and around IEC
1ch 5 x '57' , 5x '48' , 8x .39, 5.6r,4r7, 2x1k, 4x22r 1w, 6k8 2w,
4x 4560 , 70413080
SAC187, 7815, Motorola 6018 , 6019
top amp B-E op check 16R all to3 except central one
pair .65/.93 & .57/.91V
.43 and .45V to C
Topamp wires red,red,bk to ch A
ps rails .43/1.23V to white with top amp removed and bottom 
amp in place
Motorola 715 TO220 MPS ? and 2x 400R on small bottom pcb, MSM5331RS
TO126 add SJE and TO92 add MPS97 to the observed type numbers
Bottom amp ps .43 and >2V each way to white with both amps removed
front pots 2x 20K
Reseat ICs in the ps
Remove 4 rear screws  , 2 sections of central I/P / O/P boards slide out of the 
rear. 
Neutrix 1/4 in / XLR.
Desolder before removing the rear plastic plate. Metal frame anchor tangs are bent 
under the solder so beware when desoldering with hot air. Hot melt glue the Rs/TS and T pins to the 
neutrix rear plate before prizinf off to keep in register. 
Cut retaining plastic pawl before sliding out
Prize out the next section a few mm before 
hotmelting those pis in place and removing fully. 
pinning
RS  Ts  T
XLR1 XLR3 XLR2 
Ring , sw
XLR shield contact, Gnd
Gnd to SW c/s when plug is out
Cleaned the contacts and reinforced the spring action by introducing silicone rubber 
sleeving piece in each U shape of spring
Have a plug in place before re-assembling to keep the switch contacts 
on the correct sides. Push pins home until rear of contact is flush with the 
plastic matrix frame. 
Low level output and crossing over of ch a and ch B
+/-0.5V on input to board, not +/-15V. 
Removed both opamps and +/-.7V.
Managed to mark one end of 2x7 way ribbon but replaced the other end the wrong way round 
so diodes come into play and protected the opamps. 
Beware input impedance loads 600R sig gen
.3V 400 Hz isolated 1/4 in jack (not XLR one)  so feeds through direct to 7 way conn.
With front control at mid 2.55V over 4R
With XLR input 73mV in , mid control , 6.8R over 4R

Peavey Cyberbass 5 , 1993/ Neutrik RP8 connectors
Noise prolems on the midi signal 
http://www.neutrik.com/client/neutrik/media/view500/Media_1128418177.jpg
Neutrik logo is a curvy 7, T, and then upside down curvy 7
Or rather the choice of lead, presumably a generic problem so a pre-emptive
fix for these leads required, whether new or old. Apart from fixing the
break in one wire on this lead. No abuse required, they will naturally self
destruct.
8 way midi and audio lead but no overall shield and the otherwise nice
rubbery sleeving compresses/deforms to next to nothing thickness under the
plastic crocodile teeth of the internal cable grip. So the teeth end up
pressing into a single
active (soon to be not) wire in normal use. Cut a strip of 
0.6mm thick expanded aluminium sheet to wrap 
around the sleeving and go under the crocodile teeth. 
Removed the pins ,ITF, and soldered back a fresh 
bit of cable. And because the solder blobs bulged added 
some hotmelt string between pins. The pin numbering , not stated in 
the Neutrik pdf goes with the snaking of the green colouration 
on the pin matrix. Beware these cores can go in the barrel 
in 2 diametrical positions, ie not polarised. Peavey 
has used the opposite, so the green blob goes 180 
degree round from the arrow on the barrel.
Decided to reinforce the sleeving on the other plug and one supposedly
crimped wire fell out of the pin and a grounding wire was broken in the same
manner as the other end, just retaining touching contact with inside of the
shielding foil of that triplet subset of wires.
Without the casing around the splitter the ground of 
the audio out is connected to the ground of the remote 
switch via the 8 way lead. 0.15V dc drop due to 
the wire in this case,
Excessive mains noise in "audio" mode, increased 
the 100uF,25V cap in the splitter to 470uF,40V. 
on the 317T, 8.5,9.5,24V
The noise now due to cross interference from the 
midi line along the length of 8 way lead.
The only way to reduce this is to turn off the 
splitter box and so guitar ps and plug a dummy 
1/4 inch jack in the normal guitar output to engage 
the battery .
normal output range about 70mV to 100mV pk-pk 
on different strings. Without battery in, 
impedance varied between 7.5K and 9.5K on guitar 
control settings. With no power to the synth unit 
impedance across the output jack was 250R

Peavey Delta Blues, 2007
Nasty noises and a red glowing valve seen.
At 70% mains current draw of .6amp and rising.
400R W/W ok
V4 EL84 no heater glow seen but 4-5 ok, the core 
had shifted into the dome end of the tube and blocking the heater glow comiong out, 
rotate the tube in hand and a lot of noise of rattling electrodes. 
V5 its partner the red JJ logo was whitish
Tested V4 on CT160 at 70% mains , could get a balance at 26mA but needle 
went counter to normal and 3M on C/H and CH/R varying a lot on tapping.
Pair of scissor-action plectrums under the knobs required to remove them. sc along 
valve bases plus 2 offset, rear socket bush nuts releasesd. Push in the 
valve bases and wangle all 3 boards out as one assembly
ser no contained 2007 , as 8 digit, 2007, 3 digit
barcode label 09.....
pcb 7 segment overlay mark of 06334
bent and uncropped component lead , 0.5mm from shorting the Tx.
Checked 47K and 220K Rs soldering and for monitoring purposes of the grid voltage 
interboard wires 9 and 11 counted from the mains  Tx end
Plenty of ring-cracks at the valve bases in the making, not PbF but lack of solder 
for bridging large holes. Glue cons to thr boards as no catches on the headers
Tank 215R/60R
2 seriesed sp 5.6R
Hum on reverb , someone had replaced the tank the wrong way round, the input marked 
end of the tank goes nearest the mains Tx
Current draw of .4 amps at 240V quiescent

Peavey Deuce 212, VT seies, 1980 ?
Effects channel clipping distortion and fading up and down with phase f
TI  IC marked SN99661 and 70400604 and 604 on the schematic
A number of people (out there) enquiring about work-around of  replacement
with 4016 or 4066 but no reports found of reported success.
The effects out one here, at first sight is doubled up of the 2 analogue
switches, but as c/o type only one used when it somes to it. 4066 sw about
4x Ron of a TL064 so that should be ok for all 4 paralleled  for this PREA
output switching function. No problem finding space. I happen to have a
salvaged TL064 but will keep that for a rainy day. Anyone been here before
and can report success. Or a simple FET work around instead.
 PDF for the replacement of the TL604 part with a small PC board.
 http://music-electronics-forum.com/t22020/
That adaptor would work as used in this amp , as single pole change over but
not generally for the 604 with 2 separate SPST alternately active as no
inverter in that package. One of the other unused 2 in the DG211 and a
resistor could perhaps be made to invert one of the control lines.
Back working again. A neat 1 x 3/4 inch matrix board mounted vertically,
enough space, with lowest .2 inches tied and glued around an 8 pin turned
pin socket to fit into the existing socket. Bridging wires dsoldered into
the turned pins. Sockets glued together as now a rockable assembly.
This is the node map
TL604    ,    DG211
pin1 ,  pin5
p2 , p8 + p16
p3 ,  p2
p4 , p7
p5 , p4
p6 , p6
p7 , p3
p8 ,  via 10K to p13
DG211 additional comps
p1 via 4K7 to p5
p5 low side of 5V zener  high side to p12
p12 via SM 10K to p13
I've left the 2 unused 211 controls unterminated, as in pv cct,  just in
case circuit critical but probably should be tied to DC
Label PV amp pcb starting from input soxkt and outer line of ICs , approximately
U2,15,4,3,14,12,6,16
inner approximate line
U7,8,9,10,13,1,11,17,18,5
Without the o/p valves in place and powering up,use 70 percent mains for 
checking out prea
With test signal into effects ch and monitoring op pins of ICs in that chain, all good to U13
U4B ,7
U3A,1
U3B, 7 treble and bass
U14,6 post gain
U1B, 7 color
phaser U7,8,9,10 p6
U1A, 1
U13
U17 , 3 problem distortion
+/-15V at top RH corner zeners
Tx 2.7R// Y 5.4, 15.5 at diode bridge
op tx  sec 33.1/29.2
tank 57R, 182R
The 300V transistor pair are ok , as is the clean channel prea.
So called Superior Grade Cryo for the 4 op bottles
Not a socket problem but out of mechanical spec valve problem
Work ok and test ok but in use and the tester there is low
insertion/extraction force in the sockets. Dragon's teeth hold them in place
ok, so will not fall out. Measuring the pin diameters about 2.15 mm compared
to a random selection of others laying around of  2.3mm. 
Marking a line outside of the socket base perpendicular to a fork,
transfering a line to the valve base to get the correct "reversed"
orientation . Then a 1.9mm rod as a stop in the jaws of parallel action
pliers deformed the pins to elliptical axes of 2 and 2.3mm in the right
sense to increase the grip.

Peavey Escort 2000, 2003 or later
Stone chip got inside ch 4 slider and mangled the wiper
3 screws plus 2 plus 2 for the handle
ch 4 slider for one good side at 1/2 position, lower pair of contacts, measured 750R of 10K or so
2.5 to 2.8K for the mono ch1 /2/3 1/2 posistions, marked Matsushita/ Panasonic 
logo of an M in a square , M with feet and rounded corners of square 
lower logo pics on http://www.rlocman.ru/img/logo/matsushita.gif
, 10K*Y 
and the ch3 /5 ones 10K*YX2 where * is ohms symbol
wiper is 6.7mm wide, tried robbing from another pot but wrong form. 
Straightened ot the mangled wiper
So "Y law" 10K slider pot scalings, out of circuit,  are
25 percent 185R, 50 percent 725, 75 percent 6K
Digital pcb ribbon on main board is probably a ZIF connector with end clasps. 
To separate the prea needs old soldering iron heat and a blade to separate 
as the glue was runny when applied and gets inside the connectors. 
Use the blade reactively so as not to dislodge the pcb mounterd ends
U308, p7 to L master
U306 p7 to R
in and out uses DC blocking caps , wiper outputs to CN104
To get inside the smps warm the cover plate to release the pads.
ps apparently made year 2000
KA3842A , CNY17G, 
100K, R22, 2x 100K, 2K7
2x IRF840
add lacquer to ps cover sc.
all rotary and slider pots at 1/2
.2V 400Hz in ch1 , .11V over 8R load, L and R
.2V in one ch4 ip .06V over 8R L or R
single ch5 .033 over 8R , L / R
Real time , on-demand, fan control so varying speed
to prea red and blue +/-14.7V
main rails +/-34V
speakers 3.3R

Peavey microbass , 2004?
(f) .5A fuse 1.25 in , failed at sw on, no sag in the wire, diagonal across the barrel, 
loose at one end. Ground off the cap but loosened with the heat so will try soldering iron next time, 
Fuse wire physically broken in the cap , no sputtering/staining.
Replaced with (T) .5A
TDA2040, CA3080E, 2x4560D
Tx 60R//1.3R be-Be
sp 3.3R
100R 5W, 2x 100R
D12/14 +ve rail
D11/13 -ve rail
Dealt with usual suspects while in there.
If speaker lead short then R71,10R will charr

Peavey Prowler 1999
All the 1/4 inch sockets and one , only, of
the valve bases ,  bad solder joints, reacted to the re-soldering process as
though the tags were made of stainless steel or had a grease/oil film over
them. What could have been the cause?
I did notice an amount of  black copper sulphide? corrossion over the brass
of the stand-off power switches - more like usual 30 years of black from air
bourne sulphurous gases.
This was failure to solder onto the pins themselves, the pcb pad solder
adherence seemed ok.
I still tend to a production problem as just one valve base Belkin and, not
at component making, as the jack sockets are Ream UK. Maybe contamination by
flood or fire or something like that at pre-production parts storage . If it
was greasy hands of a procuction operative I would not expect both surfaces
of each tag and all tags to be affected.
I'll see if the owner uses it near an oil burner or something that may
locally contaminate. The mystery is why just one of the 5 valve sockets
affected. Until the surface of each tag was abraided back, the solder would
not take, just as though they were made of stainless steel. All the other
solder joins look perfect , not the slightest trace of greyness or surface
crazing . The owner's cat found the front grill ideal as a scratchpad for
itchy claws, perhaps extgremely well aimed cat urine, but again no
suspicious staining inside
Mains thermistor 4R cold
schematic much like Valveking 112
Tx 8.1R//26.5,.2,20.7R
speaker 7.3R Blue Marvel 8 ohm 70777104
tank 55R/195R
ps It had been kept in a shed for a couple of years

Peavey PV14 mixer, 2012
remove torx sc and IEC sc, slightly flex sides to get tangs over 
pcb , beware of snagging ribbon. Used captive nuts to IEC for refixing 
with ms sc.
Surprisingly strong "electrical" smell around the vent ports.
Blown TOP244YN , 20 ohms across rectified mains cap.
Considering crack to its encapsulation is just observable, on  one side only and then under x30. Distorted top to the sillypad (TM) , what may be a puncture hole at the non-rounded, but then not sharp, rear upper edge.
20R across rectified mains. R11 330R, R2 22?
R5 330R, 2x 5.6K
Hang on a bit , although the tab holding bolt has an insulating washer, the heatsink is isolated, anti-EMI ?. So if it did puncture , why leading to failure?
Any known problems with these presumably fairly generic SMPS sub-units, all else checks out (cold) ok. Mica will be going back in there. 
All I know is the back face is flat unlike the curved one I came across in a blown Yamaha Stagepas recently, TOP249YN , one of two push-pull , pirate or just sloppy manufacture, maybe stress relieving of the metal after guillotining/machining, developing over time.
The drummer knocked the mains lead. I wonder if there is an Achilles heel with such 110/240V mains voltage auto-sensing SMPS drivers, if there is a short duration interupt in power and then auto restart after the 8 cycles noted in the datasheet of these TOP24*YN devices. 
Reason for the tab insulator. 20mm high heatsink 2 mm from the metal chassis, so only arctan(2/20) = 6 degree, bending of the pcb would let 340V touch ground. 
Going by the curved over top of the sillypad, this has been subjected to substantial heat. This is not a mixer-amp, just mixer loads of apamps and a big DSP chip, so why the heat? Vents are either side of the chassis with no venting local to the smps which is hemmed in between chassis base and main pcb 
Decided to grind 4 holes through the pcb in the heatsink footprint and give a graduated set to the vanes, to make a staircase, either side, pointing away from the IEC, plus mica insulator for the replacement.
Perhaps the set to one side plus air from under the pcb may give some sideways movement. Despite not the slightest local discolour indication of the pcb overheating or any of that telltale dust accumulation on the underside of the main pcb directly over the heatsink. But I feel I have to do something other than just direct TOP replacement 
Putting my deer-stalker hat on. Someone had been inside to replace the fuse. Left out some of the screws, including one self-tap that holds the IEC. If that one was previously missing and the IEC just "held" by the remaining one next to the TOP heatsink,loosened by repeated IEC insertions AND the sillypad was punctured or close to puncturing. Then the drummer tripped over the lead, IEC twisted and the IEC holding screw touched the heatsink, as it is long enough, then blown TOP244, but about 4mm gap to swing across to do so. But as there are no pcb standoffs to chassis in that area, relying on the IEC screws to chassis, then perhaps the whole pcb being tilted in a downwards sense, by drummer standing on the lead, and then only that arctan(2/20) 2mm gap for heatsink to contact chassis. 
Nothing obviously loading the ps (cold) will power up replacement tomorrow, presumably 48V and raw +/-15V as only one vr on the smps pcb, component side of the big board not seen.
Looking a bit deeper into TOP24* datasheet. This PV14 has the 4 central pins connected together, 3 terminal device, which is over-voltage disabled mode.
So what happens in mains dropout and reconnection scenario, as with drummer tripping over the mains lead and auto-restart on what it erroneously determines to be low mains voltage setting. Would probalistically be the same for those floppy 4-way plastic distribution sockets, breaking and making, blowing the supply, if this is a potential failure mode. 240V in the UK.
Had some TOP249YN around so tried one in there and went in to .8 sec clicking protect mode. Thinking it was a mismatch in sense Rs I sent of for some TOP244YN. Replaced and still went into protect mode even with a load on the nominal/actual ? +15V line as that line is current monitored by a dropper to feed the opto-isolator.
Double DVM-D test on the opto in circuit showed no response. Removed the CNY17 and replaced with a 4N31 which passes the double DVM-D test in circuit, will mains power up again tomorrow .
So some overvoltage/overcurrent to the C-E of the opto when the ps failed. 
Sitting quiescent for 1/2 hour and an IR thermometer to the TOP body 38 deg C. But if you point it to the rear it picks up 78 deg C of the 330R dropper that is enclosed on all sides by the ps pcb , heatsink,chassis and main board. Perhaps over hours and lack of through draft that radiator heats up the heatsink and so TOP , enough to trigger temp protect.
Hopefully the holes I ground through the ps pcb and the staircasing of the h/s vanes will preclude that. 
48V,-15V,0,0,+15
TL431 , +15V line must be loaded as drop over L1 is monitored, 
used 56R 
replaced 249 with 244 and same protect mode.
4N31 replaced as opto
1 +2 -LED
46 5C
10R , 2 small caps + 1N4148 size diode so probably opto at 70V 
100mA  is lowest rated component in that area, at least failed o/c.
30V rating for 4N31
With 240V mains , 56R load on "+15V", 
DVM-acV 0.025V differential feed to op-amp feed forward cct.
45V,-15V,0,0,+14.9V with mixer attached

Peavy PV560
+/- 27V on umbilical
+/- 49V main rails
22-0-22 Vac
tr pr 5R
prea 2x22,2x 100, 7815,7915
pa 2x 2K, 5.6R, 4x .33, 2K7, 180R, 22R
2x 70484140, 2x 70474140 ?
70413080. 2x BA4860, 2x TO126 probably MJE

Peavey PV 900 slave amp , 2002
Loss of one channel. Problem somewhere beween the backside of the input
socket and the preamp output of that channel. Other channel traces through
ok. Vol pot tracks ok
Perhaps owners think they will be charged more for stupidity. You'd think it
was like the doctor-patient consultation.
Perhaps just a chance thing or maybe he plugged a speaker lead in one of the
amp 1/4 inch inputs.
Input to a SMD JRC/ NJM4560 stuck at 7V and its output at +ve rail, 10K in
the line not enough to limit whatever went in there, perhaps high dV/dt,
giving him the benefit of the doubt
Replaced with a pin/function  compatible SOIC JRC 4580 and so far checks out
ok.
Thermal/aerodynamic  management query.
Sensible , I suppose, the unusual taper in the cooling duct between the 2 PA
heatsinks. So 1.25 inch clear gap at fan end and .25 inch clear gap at the
other end so forcing air down the flutes, which otherwise free air would try
and avoid going into. But this skewness makes the mechanical design awkward.
Why did they not keep the regular 1.25 inch gap and fit a baffle with a slot
or holes at the other end so stopping down from 1.25 to .25 inches in effect.
Does anyone know whether the aerodynamics of a taper would force air along
the whole length of the flutes rather than just at the far end where the air
outlets ?
I think if I was going to taper the air flow, I would leave the normal
parallel gap and then a divided taper from stiff card or whatever starting
at a vertical folded edge 2 inches from the fan end , down the middle of the
duct and 1/8 inch gap either side, to the heatsinks. So, in plan, a V along
the length of the duct.
14K each vol pot at 1/2
0,0,-15,+15,0,0.09 rms chA
chB
chA
chB only DC
4sw push-push ok
JT axial .25" so. unusual tip contact, one switched and both contacts jumpered on pcb
u-metal half box screws to rear of amp under ch2 and ch7
Hotmelt over the grey ribbon ends 
Lacquer over sc of screen plate over mixer
Top cover lift front edge and slide forward
Bad solder, release the PREA board and cut cable ties and plenty of 
ropom to externalise.
Bridge mode& DOT defeat
0.1V 400 Hz in , vol pots at 1/2, 1.3V ac over 8R

Peavey PVi8B Plus, mixer amp , 2008
Intermittant loss of bass throughput. Of course not been able to trace ,
induce the problem - other than presumed PbF problem.
Also pin of phono jack broken off , jammed in x4 phono socket block
Owner never uses the monitor output. Main and monitor PA look the same
components but not mirror/same layouts. Any likely problems swapping the
simple screened leads from each preamp section and swapping the PA speaker
output leads?
Will then at least localise the problem to prea , if the problem recurs
Not a stereo mixer , the main and monitor channels are separated in the
mixer section
Problem comes through to the main amp, maybe in monitor channel as well, but
as owner does not use that and I've not been able to induce the problem I
don't know where the problem lies
I had to get inside the mixer section to replace some worn out XLR (3 years
old). I've never seen this - what happened to inspection satages in
production. ?
A 1N4148 D in ch7 , D2, the cathode had never been placed through the
pcb let alone soldered. It had its lead bent at placement and ended up
component side , squashed under the metal shroud of the main level pot of
ch7, so grounded, should have gone to pin 9 of an 074.
I doubt it is the tinny-sound problem source though
Knob colours
GGG RR
G R 
R
W
main GRG BBB
For ease of use on the bench , cover that bright blue LED with some tape
Reinforced 1/4 in input socket with tinned wire to solder point down-trace. 
Swapped input signal leads, melt off laquer or housing will come off pcb not header part 
from socket. At the speaker output header disengage crimp pins and swap the leads over.
Label inside the swap over for the next person.
No 1/4 in sockets had a bypass function as far as I could see.
Soldering ch7 diode as intended made no difference so perhaps something to 
do with clipping situation.

Peavey PVi8B Plus, 2008
2 years old
to remove rear panel remove 2x2 side screws only
front 2 top and 2 bottom screws to release
th sw n/o 95 deg C
2x 47, 2x10, 6x .33, 3k3,6x10R 1/2W, 
6x 2sc2500, 5x 2sa1943, 2x TIP122, 2x A1837, 2x c4793, 
loose rear 1/4 in socket and so messed up solder, 2x TIP122 + 1 ?
4x b649ac , 4x d669ac
main at o/p end , mon at tr end
+/-14V and 48V on umbilical
Of volcanoes and caldera
Continuing the metaphor. 2 yearold China-made Peavey i8B Plus mixer amp. No
reference to RoHS or PbF as USA company but volcanoes with loads of
"caldera" in the making (part formed ring cracks in solder points) . 2 forms
of intermittent distortion. Resoldering the usual suspects cured the crackle
but not the other metalic triangling and tending to half-complementary
waveform diistortion. Could not induce this one however much bashing with
biro barrel. Eventually with some long-nose pliers tugging, heating and
freezing and vibrating with nylon bolt in an engraver tool, the fault
emerged long enough to take some erroneous DC and scoping to determine which
1/4 (1/2 of one ch) where lay the problem and but no closer in than that.
Redid all solder points in that 1/4 and ps and not returned since but will
it come bouncing back ?then there is the other channel for new failings
When bad Vb of Q109 was 0V on main amp
Good Vs
Q127 -1.06,1.03,-.4
R165 -.4, 1.03
RF207 71.5,1.1
Q107, 70.8,1.03, 70.2
2W 3K3 may need upping in wattage
cut a slot on the pcb edge for the wires to the th sw to pass through

Peavey Studio Pro 112, 1988
Mains Tx 240 V setting ** Bk, Y,Bn Fuse * Bk
pink, *, Blu * * *   *
bad norm gain , reverb ctrl
hum with any reverb level , with bright set then ultrasonic oscillation will burn 22R of zobel
Tank 93R , o/p 360Rand no ground interconnect , tank 20-69-89 (or 99 ?)
reverb tank
Well I've not seen this type before,
2 springs and 2 coil frames but only one sping per frame. So on diagonal ends a frame and on the opposing 
diagonal a taught wire link connecting the "dead" end of each spring.
Obviously less mechanical power throughput compared to 2 or 3 coils per frame, offset with more electronic 
gain presumably. So change of tonal structure? more bass component equivalent to a tank of twice the length? 
or a longer reverb time? or both? 
Tighten TO3 sc

Peavey remote footsw
Tip to ring s/c in one set of sw positions only DVM testing, ground line broken at socalled 
strain relief. Mole grips to release and grind back part of inner "blade" and reuse shortened lead

Peavey PV 2000, 2 x 1KW, 30Kg, 2001
Central TO3 of mainboard N and P sides is not 
configured as the remaining 7 TO3
Mechanical problems that need sorting before the electrics or will  recur.
Each channel has 2 "daughter " board output arrays with power rails via the
aluminium hex bar standoffs. One end has the screws nicely soldered on to
the main board conductor traces, but these standoff boards just screwed
against polyester pcb board, no star washers, contact (in theory) is on the
other side of the board, but not with loose screws. This amp is used in
alternately both damp and dusty environment so inside looks more like 20
yearold, aluminium corrosion etc.
Any mod better than cleaning faces and adding star washers ?
Also the clinch nuts that hold the pa boards away from the top and bottom
covers are just clinched into pcb polyester so easily turn and work loose,
any mod for that ?
There was one zinc plated nut with captive
star washer , loose inside, causing trouble. Now I've found another one,
lodged safely, in the base. Came from the IEC housing. The real culprit was one of 
the mains cable clamp bracket-looking pieces had dropped away and 
retained by the owner after he had looked inside. They are loose fitting ,32 TPI , on the other
0.128 inch screws used inside , so presumably 6UNC. As this is in the UK,
unlikely 2 would have fallen in the fan access , in a metric-screw UK.
Exactly these style nuts are used elsewhere in the amp , but the next size
smaller. Most screws in there are tapped clinch nuts or chassis steel.
This amp is 30Kg in weight  and because the clinch nuts are so small and
flexible top panel, so close to the pcb, someone has post-factory lined the
panel with sticky thick plastic sheet. You cannot extend the "nuts" without
modifying the single internal bracing metal (full-on engineering).
The found nut had no sputter or smoke marks unlike the pcb.
Re-clinching with a ground down cross point driver bit and anvil etc, worked
well, retapping with 4UNC , because of the corrossion rather than any
deformation by my action.
1 of the 2 nuts holding the IEC socket was off. I wondered why the owner did
not hand me the "lump of metal" that he discovered wedged in an active area,
he probably dropped it trying to retrieve it, from a visible but awkward
place. The screw was in place , with a tight fit , not threaded, through the
IEC. Owner out of contact for a few days, so stymied , in case I'm inferring
too much, ie 1 nut only.
More accidents waiting to happen, presumably because this amp is used
outdoors at full 2KW whack. Not only the screws holding the daughterboards
to the pillars but the pillars to the soldered-in-heads mainboard screws
undid in the range of 0.1 to 0.2 N-m , presumably due to creep of the pcb
polyester. So presumably a generic problem for all these sort of Peavey
amps. So 3 stainless steel star washers each on these active pillars, longer
screws and laquer over the exposed screw heads.
The hex pillars have been cut with star patterns on the ends which just
grind into the polyester on tightening. So I've changed my mind to abraid
the pillar ends , 3 st/st crinkle washers , longer screws and laquered heads
Looks as though the diac/triac is for crowbar protection of the speakers
from DC fault developement in the amp. On the assumption the mains trip will
trip.
Thermal swittch Asahi US602 S
I find one www ref to this as 140 degree F = only 60 deg C, mounted with
direct thermal contact on TO3 package, 60 watt in use,  MJ15025. Surely
higher than that.
accurate kettle test can only take to 95 deg C and no switch over.
Less accurate hot-air gun switches at 95 and reset at 75.
As there is also SELCO OA212 printed on the active contact face it is
probably, n/c,100 deg C
shorted SAC187 ( across speaker o/p) replaced with BTA16-600 
Test the 8V bidirectional switch diac marked C8D C1 ? 
= SBS/4 on a current limited 50mA >8V bench ps 
when triac is removed
70474200 replaced with MJ15025 and 70484200 with MJ15024
lower amp is "B" red power leads
Release rear, base and central galvanised divider bolts to slide remove 
the bottom amp leaving sides , front and 2 grey plastic bracing rods, 
undo earth wire bond screw
leave IEC and 7 amp cutout in place
mains transformer primary 2.9R
uses 16x .33R, 2x4k ,2x 5.6R, 70413080, 2x 4560d,
MJ350, MJ340, 6.8K, 47R
fan & o/p board uses 2.8K
mark orientation of LV board connectors as 
central one is full 5 way
90 percent of mains , 210V ac 
monitoring bottom amp ( top one removed) +/- 80V dc 
gain at +6dB , 0.2V 400Hz i/p 
gave 5V ac over 4 ohm, and about 1amp mains current
Ok last summer, stored in an outbuilding over winter , got down to -15 deg C
southern England 2010 December.
Now one channel shows DDT (distortion detection technique),
protect LED on .  Nothing seems amiss cold testing on that channel, not
powered up , monitored , yet. I have a schematic for it, a lot of socketed
op amps in that area,  so changing them and the sockets would be a good
start methinks.
looks as though the precipitating problem was failing 15V zener.
For some odd reason there are LV +/- 15V LV supplies and +/-15 supplies from
the +/-82V rails linked together via diodes at the pa.
The LV +15V supply is from 7815 but the -15V is from 1W zener. The -92V
supplied 15V zener stable but the LV one starts at -15.6V (diode offset from
the other one of 15.2V presumably) and drops through 15.8V . When the
difference between nominal +/-15V rails is about 1V it goes outside the
capture range of the half U100 dual op amp that feeds back correction into
the pa bias area (why there is no bias adjust on these amps)
Q102 ? -15,-.4,-.1
Q105 -.4, -87, -/8
Q104 -.4, 87, -10.6
Q101 .1,14,0
Q103 0,15,15 / MPS6534 ? replaced with 2N2509A
Made 5 pin extender to probe component face powered up.
If bottom amp fails then perhaps swap to  top to work on.
Double diodes under h/s measure 1.12 and 1.22 DVM diode test SZ13886-2
Added 33R and 2K preset over CR10 
Changed Q103 to 2N2905A
Added 18K from -15V ot emitter of Q105 and protect LED went out and 
output stabilised to 0V
Replaced with 10K and 100K preset.
1N4744 on LV pcb was drifting starting at 15.6V and eventually goiung outside opamp 
capture range.
With mid vol pot 92mV in 1.44V over 4R 
Upping throughput at about 15V ac over 4R the DDT LED came on and o/p limited to that. 
Same settings on good ch passed that power level easily.
Probing lower board V , in place, managed to short Q104 H/S . 
As a check the V on HS of each TO125 should correspond to the V on th emain top TO3 h/s. 
Blew R133 4R7 fusible resistor.
Fan control cold 1.1V on red lead, one control line only , both channels 
are in parallel to the MOC opto LED.
Somewhere between 330R and 470R across when active via one control only 
changes sped from min to max
Q104 1.2,87,1.8
other TO126 0,-87,0 otherwise good ch no false yellow protect LED
outputs of opamps are 0,0/0 at fan control end and -13.-13 at other end of main board
To remove bottom ch B board
Remove under screws, 3 at rear, mark all cables, release 3 from LV board
and mains Tx, undo fan supply and earth point. Release the steel internal divider section. 
Undo rear plate leaving fan and IEC in place. Remove amp along withe steel divider swction. 
Fan control has hysterisis , not proportional, check with LED instead of the opto  and hot air 
over the area containing the h/s sensor.
Connect ls ground 
Q104 -.3V, +87 ,-9.1V
Q105 -.3,-87, -.6V
Loss of the negative side of the biasing area of one channel. By
a secondary route there was some negative V around , did not rise to + rail
or centre and difficult to find
as no reason to suspect a small o/c R. In an area with only -15V secondary
supply and loads of  1N4148 and TO92 around. This resistor was normal 1/3W
4K7, not a fusible resistor, metal oxide spiral construction. On scraping
off the coating , break was 1.5 turns along the 5 turns, ie not central.
Absolutely no sign of heating on original R surface or the board and no sign
of heating with the coating removed. No more than 15V in that circuit area. 
A closely defined break , probing with
DVM.  under x30 magnification there was a patch of missing MO presumably corroded 
and pulled away on my removing the coating. 
The failed section was
distributed , puckered and a bit discoloured presumably from
condensation/corrossion and parts flaked off 
Could not close the break by
twisting or bending the body of the R.
I've come across mechanically broken R from being dropped but never from
cold or damp.
Double diodes in biasing CR113 dual diodes 1.37V and 1.43V at 10mA measured on SZ13886-2 .
The outer casing screws are metric 3mm and 4mm not UNC, may need clinch nuts retapping 
if binding on screws

Peavey Rage 258, 2006
Blown mains fuse.
Replaced but intrusive hum/buzz on output 
and suspicious black ejecta on the output pin , 
replaced the LM1875T with TDA2050 
and high power 5V zener in each ps line.
Specced at 25W but running at +/-30V rails so 30 W , 
which for 8R load is in the device specs but 
seems odd as amp blew at very low loudness (so 
high rail volts ?).
2050 specced only for +/-25V
Tx 44R// 1.3,1.3R
1W 2x 470, .33R, 10

Peavey solo series, Bandit 75
Intermittent audio cutting out
Nothing specifically found but attended to 
the usual suspects.
Resoldered jack sockets
Reconditioned very worn/scratchy vol pot
One 8 way DIL socket may have been dodgey, 
replaced with turned pin socket.
Cleaned the effects socket bypass switches 
in case of corrosion there.
If it had returned then would have replaced 
other 3 DIL sockets and 12V DPDT DIL relay
O/P SJ6392 and SJ6505, 45, -45V on Cs
0.5,45,1.2V and -0.5,-45,-1.2V on TO220 devices
14.5,-14.5 to 15.5,-15.5V on ICs

Peavey Solo special , 1981
Owned from new by owner, but stored in a garage for years
Dropped to less than 1/10 volume and clipping  and long term problem with tank. propping 
up the amp would "sort" that out .
Chassis bolts, short to front and long at rear
4x SJ6392 5W 2x 250R, 5x R33, 10W .1R
1W 1K5, 2K7, 22, 2x 4K7
3 x RC4558, 1 MC1458 dated 1988 prob replacement
+/-39V , +/-25V
Part of PREA out socket turned and touched PA-in , re-aligned and hotmelt glued into place solved vol prob
5mV 100Hz in , all controls at 1/2, reverb at 0 as causing the clipping, 
gave 3.5V op over 8R
Tank 54R / 179R , Accutronic 4EB2C1B / 25 8123 / 7120-11114
22K to pin 5 of the MC1458 
TO126 voltages
37,1.2,36.3/.6,37,1.2
-.6,-36.8, -1.2
Adding 180R over the tank reverb i/p to amp no cliping 
Corrosion on tank phono plugs and sockets 
Accutronics 4EB2C1B, 25 81237
Normal ch by footsw only
Reverb =tip/ Select/effect = ring
speaker 4.8R (12836) 710 - 11114
Tx sw 185/80
pots 1378115 etc
tighten TO3 nuts and varnish
Footsw TSR, reverb T, R select/effects

Peavey Special 130, 1983
very low output
3.4R scorpion commercial duty 12" speaker
Tank 58R/197R
400Hz 13mV in high gain, with all mid controls and 21mV over 8R
Bad PA rear socket switch
Tighten all nuts and fuse holders
Disc of material cut from a reticulated foam pan scourer and contact glued 
over the hole in the speaker where there was foam at some point. Check by laying horizontal 
and banging that no crud is inside before sealing up. 
An insect had got inside and body fluids stuck to the VC causing distortion at certain f and level. 
Had to cut 3/4 around the dome to remove it, also part of the dome was unglued
PA in is white lead to tip contact
repaired, 6mV in of 400 Hz , all mid controls , high gain ip, 10V ac over 8R load
There were 2 piezo tweeters in this , don't know if originals or replacements but the 
holes for them made crudely, not wired in at all. 
For minimum intrusion as nothing to go by, wired both in series and 100nF/250V polyester 
cap in series as the tweeters were responsive below 1KHz, owner did not return 
so presumed adequate top end

Peavey TKO 115, 1992, 30 Kg
Nasty hum and tripped out a RCCD. Speaker 
probably had DC on it. Probably due to being 
dropped, one ps cap broken away and the other 
loose at pcb joint. 2 pots had broken paxolin.
Remove 2 top braces and rear angled screws to remopve amp.
Careful of these pots on removing the pcb as 
not really enough leeway to extract comfortably.
Had been repaired before with 2SA909 replacing the 
original 70473100 (MJ5016). Original 70483100 
(MJ5015) in place and both OK.
Also used  SJE5332 NPN  , SJE5331 PNP.
Resistors 3x150, 2x2K,2 x0.33.
ps +-50V, +-27V
Front grill frame needs banging in at each 
corner with hammer over a  wooden block 
(heavy duty velcro-like fixings) prize apart 
to remove

Peavey TNT 115S BW U1 , 1999
S for Sheffield perhaps
Cutting out intermittant and intermittant hum.
bad solder on input 1/4in weak sockets, replaced with wired-in upside down proper ones.
Tr 4.8V on 220V setting and 5.3V on 240V , as found in 220V setting , red hotmelt glued 
in 240V posistion. 
Sec .2-0-.2/ 2.8-0.2.8
Cold DVM D test TO3 cases to gnd , complementary pairs of .47V
Speaker 3.3R
4 screws under and 4 at graphic to release prea
Another unused socket bad solder, all other usual suspects resoldered on prea 
and pa. 
PA all TO3 and TO220 screws not tight 

Peavey TNT 160 , 1990
Highly unreliable, assorted noises, hum etc, or no output 
after using external; input, to bypass internal prea.
5 of the 6 front panel jack sockets have duff solder. Not even with
lead-free solder have I come across such  .
What other problems with these sockets ?
http://www.diversed.fsnet.co.uk/peavey_0.25.jpg
sockets marked S/C, barrel/cylinder ground contact and sprung tip contact
with switch contact. A different 5 of the 6 have a crack in the plastic
showing at the tip of the yellow "V" - stress from manufacture ? metal bush
and nut so the plastic should not be compressed/stressed. The ground
terminal wire seem to be just pressure contact to the barrel to the left of
the V, with green copper carbonate? corrosion products, either side of that
ground wire.
In this case its that old problem of thin blade terminals soldered into
circular holes, so an enormous bridging gap for the solder in most places.
My usual retro-remedy is discs of fine brass or copper mesh, punched with a
paper-punch , and opened out central hole, soldered in place over each pin,
so mesh reinforced solder.
pcb test loop pin soldered soldered between each pair of sockets , plus 
2 more holes, silicone cordage tied around with a small ceramic bead over 
the contact blade to reinforce 1/4 inch plug/socket closure force.
Thread cord through loop before soldering to track on rear of pcb.
Earth point totally loose as were some of the pcb retaining screws 
from combo vibration.
Either or both ? loose mains earth or not tightened 1/4 inch socket nuts 
was giving electronic "phaser" noise, whether switched in or out, 
on reassembly until both corrected. As usual with Peavey, I don't like xternal 
240/120V switches in UK use and placed a solder tag under one 
mounting screw to physically hold off any drunk/thicko fiddling 
trying to "repair" the amp at some future stage.
Uses 2x 3034140, 2x 7048140, 4x .33R, 2x 2K, 2x 5.6, 2x 2.7K, 7815,
7915, 2 motorola TO220 , 70487478, 2x4558
prea NE572, MN3007, MN3101, LM555, 144558
transformer 5.6R// 5.2R, .4R
interconnects -14,0//-16,0,15,0//0,0
TO220 1.2,45,.55//-1.2,-45,-.55

Peavey TNT1155 B W Combo Mark III Series,1979, 35Kg, 130W TNT115S ?
Series 260c
trannies maybe FETs TO92 size marked
Korea  TIE626 or TI6626 or maybe T1E626 or T16626
also a number 761, no equivaklent found.
pa 2x tl074, BD139, M926(0(?53?/5332, CA3904
70 4 / 874 78, RCA 532
The output trannies 67376 , RCA 
Bad crackles/bangs due to corrosion 
of Molex type connector pins removed 
pins using method for QM pins 
in tips files.
+/- 40V, +/-15V
10W, .1 and .33x4
Load tested for 6V of 400 Hz into 4 ohms 
heatsink temp stabilised to plus 
38 degrees C over room temp and .3V ac at 
preamp to amp connection

Peavey Valve King 212, 2010
only 6 months old , barged into a door , stove in the standby sw, shattered the bakelite, and bush nut flew off 
but stem stayed in place so someone decided to power up. No
mention of what happened when powered up. As found the rocker contact in the sw was touching 
the metal of the sw surround.  10 watt 400R , R201 resistor overheated to
burn up cabling and black "candy floss" everwhere inside.
anyone know the DC ohmages of the transformers ? These readings look ok
, genericaly speaking
o/p primary 29.8 (brown) /24.6 R swapping this around will lead to weird feedback/oscillations, 
particularly when playing with the "resonance" pot on the back panel
mains primary for 240V 4.4R
sec
heater 0.4R
HT 14.2R
other DC 74.4R
To remove amp , as tight I removed the front facia strip 4 long plus 2 short PK to give some space. 
Disconnect speaker lead , reverb wires , cable tie and speaker jack , then 4 top panel wood sc 
then main 4 bolts. 
Large Rs are pillar reinforced but not the LED power lamp which will shake loose so bulk up with 
hot melt. 
You would think that a 10W resistor marked on the schematic as a safety
device would mean that any wiring would be loomed away from it, not laying
along its length. Another safety issue with these amps, I was trying to see
where the chunky HT wire to the output amp was, but nothing obvious. It is
in the grey ribbon umbilical , >500V rating on that stuff? I doubt it.  6
months old , no warning signs of crap solder used, no PbF / RoHS /N 
 CE mark on internal paper label , for export, 240V structured amp, just a wheelie bin
with an X over it.
At least the OPT wires are proper 500V rating. I ' ve now marked that
connector JIC.
Someone else with  ribbon problem was initially the euro-crap solder inside 
then arcing.
I've pared off the HT wire and spiral wrapped some sleeving around it. The
wiring to the standby switch will go the other side of the main caps not
over the replaced 400R 10W dropper that had exploded to 3 bits in the
conflagration, a 4mm bit measured 46R so probably was 400R originally.
Relays click over at 50 percent mains
75 percent mains (as no valves inserted so no loading) 
176V/160/21/263V
4 large sc for the 6L6 cage

Peavey Valverb, 1994 valve / transistor hybrid
Valve Reverb, 1U case prob. 1994 , no output.
One obvious problem. Seems to be C-R-C-R-C HT ps with
the first R overheated to partially white body and O/C.
Scraped back and remnants measure 4K and 12 K. Comparing
with other MO 1 W Rs, band positions on bodies, the band heated to black
was
probably gold and the first 2 Brown then blue , third is gone totally,  .
so maybe 16K , replaced with 2 x 0.5W 33K, not higher wattage .
Supplying HT to 3 valves 12AT7 and 12AX7 so common enough.
The second  dropper in
the ps drop down chain is 22K and looks fine.
Apparently no separate secondary for heater voltage - seems to use the
same LV winding used for the transitor power rails.
Wax coloured hot-melt glue, not wax under caps which looked fine 
as well as all else.
What I thought was just an intermediary smoothing stage is actually also a
feed to a 12AT7 via a presumably impedance matching output transformer
 to A2 anode and the other via 47R to the A1.
This transformer unpowered resistance seems ok about 2K on high imp
side and 300 on low imp which directly connects to one of the coil
type transducers on the spring-line. So maybe excess current in this valve
hopefully rather than a failing impedance matching transformer.
I've only ever come across piezo transducers on spring-lines before
this is 56R on the send? transformer connected side and 196R on receive end
coils.
I replaced with same wattage R ,disconnected valves and cut trace to
matching transformer.
Powered up via variac to full, giving unloaded HT rails of 440V or so
sustained with no problems.
On load hopefully the 440V should drop to less than design
max of 300V.
Dug out my old Avo 160 valve tester , noticed
last
calibrated in 1984 for the REME in the Hebrides. Also powered up via
variac initially. All those thumbwheel switch contacts and other contacts
that
could easily corrode but no problems.
I'd forgotten about the sequence , balance mains V, heater check, cold
insulation then hot
insulation , Test and Gasified check. Also forgotten that nifty 'telephone
dialler' for set mA/V.
All 3 valves nicely in the green GOOD sector. For the 12AT7 design
value is 5.5 mA/V and on test is 5.4 and 5.9 for the other triode.
Ignoring the drop associated with the other 2 valves and not
at the moment knowing the actual anode current, if at the test
value of 10mA then drop over 16K would give a dissipation of
1.6W. I cannot find in the data book or tester manual whether
that is 10mA each triode or combined value but I assume it
is per triode and 20mA if both sections on at test levels so 3.2W.
Didn't think to check for primary to secondary short on the matching 
transformer. This was the problem , the bobbin is made of soft plastic 
and with time/temeperature the ends had flexed enough to allow 
some of the outer, LV, turns to drop into the HV turns area. 
Removing the transformer and deforming the bulk of the colis 
showed changing bridging resistance. Resistance of LV coil 310 ohm 
and 2100 ohm for HV. Weight excluding bobbin about 40gm. 
Average 'circumference' of LV coil 83mm and HV 58mm.
Wire 4 thou or 42swg so resistivity per 1000 yards 1910 ohm and 
weight 0.145 lbs. So by weight predicted number of turns 1150 
and by resistance 1790 turns. Warming up the coils with low set 
hot air gun and removing vinyl tape and waxed paper and mounting 
on coil winding machine gave counted-off number of turns 1800. 
Before rewinding adding some vinyl tape either side of the 
core and against the former, so that this coil doesn't slip 
into the HV coil through the gap.
As HV section left undisturbed then implied by resistance then 
about 17,500 turns for the HV section.
Representative voltages , no signal, controls at minimum
HTs 410V,246V,194V
At fuses 20V,20V ac
On 22uF electrolytics 0.6,0.6V and 4.6,17.6V dc
On the 3 valves DC
142,0,1,0,0,125,0,1,5.9
136,0,0.8,11.6,11.6,192,13,36,5.6
232,0,3,17.5,17.6,232,0,3,117
Also disabled the 240V/110V switch for use in UK - fiddlers 
moving switch setting in USA would do no harm but in UK 
a different matter. Some point in the future stops working 
so lets turn/move every exposed switch and knob.

Peavey XR600C, 1990
Signals at op sockets but only low level speaker o/p.
Failed bypass sw on graphic  "In".
Desoldered both graphic ones , cleaned up , added 
some silicon rubber under the contact and swapped over useage,
Replaced broken 4.77mm plastic pot shafts as per tips files
Ombilical green -15V, red +15V
400Hz 10mV signal gives .26V over 68R at o.p
PA 6 x .33R, 2x .1R
70484140 x 8, 7815, 7915
2x 2k,3x1k,5r6,2x .1R
4k7, 2W,22R
TL074,7048748
3x motorola TO126b 
mains primary 3.4R
Numerous bad or going bad solder points on the Swichcraft axial type 
1/4 inch sockets, presumably strained in use.

Peavey XR684, (no suffix) 2001, perhaps similar to XR1204
Stereo splitting of ch 7,8,9 via "sectret sw" on right side of facia
Various bad solder for XLR , phono inputs etc
ch 5 and 6 lower gain than ch 1,2,3,4, XLR inputs match the gain of ch 1 to 4
+/-15V to opamps ok
6.4V at U100 inputs but 5.8V inputs of U500
ch1 Qs -1.4,6.6,-.7/-.6,6.5,-1.3
ch5 Qs -.7,5.8,-15mV/-12mV,5.8,-.68
C606,R605,C627 joined
ch1 .12V 400Hz in , 1.2V opamps i/p, 6.2V at o/p and clipping LED
ch5 1.2V  in , .03V \t opamp i/ps , .14
Replaced IC500 NJM2068 needlessly with 4560
Lost a caged nut , springing off at unclipping to get to the prea pcb.
USA 3/8 10-32 of course. Starting with smaller 2BA ? ones drilled out and retapped 
to UN 
Reassembly place front panel in first as Tx obscures main ribbon
ch2 5mV in , all mid controls , 400Hz, 4V over 8R
.2V op with 25dB pad
ch6 .1V with no pad i/p to 1/4 in so
2.3V over 8R single-ended input to ch6 XLR i/p no pad
3 zinced sc for easily forgotten netal shield and foam over Prea

Peavey XR800F
mains tr 1.6??1.1/.3R
8 x .33 5W, 2x 2K7, 6K8, 4K7, 2K7, 1K5, BA4560
th sw n/c
unplugged speaker lines measure 4K9 over ps at pa
Bad IEC solder, replaced 20mm fuse holder 
some poor TOP66  solder 
47R over B-E on one pair of TOP66
Testing open without cable extenders, handle near mains fuse , 
transformer over front ledge at umbilical, cable ties and lacing 
cord through fixing holes .
43-0-43/ 20-0-20 at 220/240V mains

Peavey XR 886, 1997, mixer amp
Bad airflow, not to the extent of tripping any of the thermal switches but enough to
concern the owner into trying to improve airflow - admirable thinking for a
non-techie.
Blowing upwards into an adequate , for fan blown, heatsink with a bank of 12
motorola 70483080 TO3 . As far as I can see the 2 uncut-down heatsink vanes
that go across the fan do little functionally for cooling and probably
disrupt the air flow.
The air has to come in horizontally under the base , up the one inch of fan
axis and then have to abruptly divert horizontally again down the 2
(separated by these vanes) relatively small channels in the heatsink.
http://www.diversed.fsnet.co.uk/peavey.jpg
the 4 inch fan removed (position marked with
Fs )along with metal sheet that encloses the heatsink. The view of this amp
is upside down as the fan is at the base. So drawing air horizonatally
theough a "designed" 5/8 inch space under the amp. Air then goes through the
1 in of fan vertically and then has to sharply divert horizontally to flow
either way through the 3 ducts in each direction. The central duct contains
no active ducts and as far as I can see only interferes with air flow as
they are right up against the fan housing. Air then vents mainly at either
end when the metal closure in place with not enough space to add a fan or 2
at those points and nowhere near the mains transformer and main air outlet
vent . A lot of venting must go up and out the mixer pannel slider holes etc
as well. The 2 TO3 mounted thermal switches are marked S and restrict the
air flow through the uppermost duct in the pic, the leads and spades as much
as the switch body. 
Actual problem was intermittant loss of one channel 
due to poor solder on a 1/4 inch spade buried in the pa.
mixer section not looked at
PA uses 2x MJE15033, 2x MJE15032 4x 3460 
2x Harris 7041 3080 
4x (2x250R , 1K)
12x 70483180 
4x (2K , 3x 0.33)2 x 5.6R
2 x motorola SAC 187 triacs
Changing switch selector from 220 to 240  dropped mains Ac from .8 amp to .6 amp 
with no signal throughput.
separate bags for screws from left , right , front , back, 
top, base, pa
55 - 55ac supplies
pin line under ch2/3 sliders, no signal
0,.43,73,.57,0,-.42,-73,-.55,-1.1,.27
load test one channel giving 8V ac into 4R 
at 400Hz. Masking off whole of mixer section to 
block off air flow through there but not back panel 
so treated nor gaps between top and botton sections.
output air rose to 9 degree C over ambient in about 
15 minutes with extra 1/2 inch added to each foot 
and plus 10 degrees for existing feet depths. 
Fan came on full after about 10 minutes of such use.

Peavey XR 886
dropped about 4 foot and then smoke 
physically broken mains fuse holder but fuse intact and burning around solder points 
and also IEC pcb points
mains tr <>10R
phono sockets on top needed replacing
remove that side of mixer  1/2 screening plate, marking position of 
stand offs and screws, also rear screening plate that fouls it.
4 in one plastic matrix all mangled , replaced with 4 standard chassis phono 
so. Fix the 4 solder tags to a central nut and bolt with scraped back chassis for 
grounding, before inserting the phonos 
and their back nuts. Phonos requiring hardware screw cups under each to 
pad out the now oversize holes. Solder 4 long wires to pass through pcb and solder when completed 
reassembly and good quantity of hotmelt all around to reinforce mechanical strength .

Peavey XR886 mixer amp
Speakon speaker outlets carrying output via the monitor route , via
monitor1&2 faders and mon1/mon2 rotary controls on each channel. But main
sliders per channel and 2 master sliders only control to phones output. I'm
loathe to burrow into the mixer (all those damn fittings) if its a RTFM
thing or a missing jumper lead , secret switch combination or something
silly. It was lent to someone and came back like this and no
knowledge/divulging of course
Zero of TO220 VR to 2 pin from outer end of ps 8W Harwin to mixer.
Then to Mixer ground , that zero via third of 3 of 5w back to PREA and wide 
trace to each of the PA 10w headers.
Its annoying the easily overlooked significance of the "o" and "."
distingushing mono (monophonic) from mon. (monitor), why not fold. instead
of mon.   .
Looks as though its diverter switch problems on axial type 1/4 inch pcb
mount sockets. Oddly both failing at the same time , perhaps someone tripped
over leads, but even then ,both failing together seems odd.
Physically jumpering master L line-out to PA-in L, and same for the right
brought normal operation. Since plugging in jacks, Left diverter is now
working as default structure of master to PA and the other one still
erroneous.
So looks as though I can leave the mixer intact and just replace the back
board patching sockets.
Not so simple. The sw on these sockets are not used, sensing must be via the
ring contacts and analogue switches or relays .
I suspect the owner could tolerate a pair of  patch leads jumpering master
outputs to PA-in
For the moment I'm going with a bad PA-in bypass switch , so replacing both
1/4 inch SWC make sockets and bad solder on a 6w  header that carries signals to 3 of the
4 control lines of a MAX364 quad an. sw IC.
6 wire p3 to p6 of the MAX near pcb edge and p3 of 6 to p3 and p11 of the MAX
If its a problem involving the recessed L/R // L+R/Mon1 mode switch then it
can stay there and as owner does not use monitor outputs, he will have to
use a pair of jumpers on the rear.
Half box , mu metal goes on rear with fixings under ch 2 and ch7 i/p
Hotmelt over the wire ends of the grey ribbons
lacquer sc of screen plates under mixer section

Peavey XRD680, 1996
Loud cracling on output 3/4 hour into a set. 
Also, previously, tripped over lead and guts of a Neutrik NC3F1P line socket 
pulled out
Knob colours
G, Bl,R,R,R,G,W per ch, controls area W,G,G,R
Take mixer apart to get to XLR, bend back soldered pin  that had pulled out of 
the pcb. Open the internal hole for this pin to make alignment easier and push
back and solder. Bad solder on another XLR socket so redid all XLR solder and 1/4 inch 
Bad solder on overheated Rs and Zeners of secondary supplies
Tx 4.3+1.9//2.7+2R7/ .2R +.2R
Failed contacts on the thermal sw 8082-723-L95, grind off the rivets to remove and replace. 
Why bad not known as had never cut out in use before .
th sw warmed up and the contacts were ahmic to 27 ohms or so , at lower than trigger flip temp.

Phonic 12 Impact, 12 channel mixer, 1981
Failure of pan operation on one channel.
More importantly the mains earthpoint did not have the casing 
paint removed either side of the earth tag point.
Each channel section is removeable after removing all bush nuts, 
XLR and slider screws. Uses 4558 and 2068 ICs.
Removed pan pot, reconditioned, squashed the swaged 
connections to the conductive tracks, resoldered nearest solder points 
reassembled and all seemed ok.
AC measured at the fuses 27,19,19,7 V.
PS uses C2336, 7815 and 7915
Molex DC readings 0,0,1.8,0.0
15,0,0,-15
15.7,0
C2336 , 2.4,68.7,1.9V dc
On main 12 channel 'bus' line 11 is -15V,line 12 is +15V.
One screw of the end cheeks is smaller than the rest.

Phonic 12 Impact, 12 channel mixer
Intermittant crackle, not able to induce via twizzle stick, 
freezing or heating anywhere.
Crackle was more high recurrance rate rustle than high voltage 
discharge. Changed mains fuse holder  fuse , internal fuses, 
tightened holders, changed +-12V regs, all associated 
electrolytics and remade all solder points on ps board.
May have been running hot with original V regs.

Phonic 620 , 2005
Bad inputs , wavering volume
Mains Tx, from white 19V ac, 19, 52, 10.5, 22,22
1/4 socket pcb holes are too large even for conventional solder
Where holes are drilled for thru-board components but of diameter far too
big , thru-hole plated , but no eyelet/inserts used to fill the gap. So
1N4001 size leads in holes twice their diameter and 1N4148 in holes twice
their diameter. So not a case of only one drill size for all. So in area
terms about 1 to 4 ratio of  lead to solder. Bad enough practise with proper
solder but with PbF, ring cracks starting all over.
Is it to avoid mutiny by the by-hand board populators ?
Added laquer to pcb screws and attended to speaker outlet solder JIC

Phonic 1062 mixer amp,2006
1 channel only, no phantom
Elektrotanya SM is for the linear ps version and also lacks the power amp schema in full etc, no other schema 
found.
I've not tried powering up since on receipt , removed from the cab. Exploring cold first. As ps rails are paralleled 
for the PAs, the ps must be ok.
What are the 2 black epoxied lumps labelled POD1062X that look like epoxied torroidal chokes. But according
 to the (wrong) 1062 version schema they are an IRFP250, presumably 3 pins, 1 pin obscured.
Rail switching between 40V and 70V rails + & - on power demand.
Anyway cold testing , seemingly as inductors , one is s/c and the other o/c which explains why a toroid with 2mm 
diameter wire wrapped around it can be o/c with no hot spot,at least, to be seen. So if mainly a powerFET, 
what else , not suggested on the schema, would be under the epoxy?
in this pic with red Xs
http://www.diverse.4mg.com/phonic1062.jpg
all o/p devices test cold DVM-D ok, so a shorted rail switcher makes sense and goes into protect mode on one 
channel but there is 2 of these POD1062X per channel and only 2 here, unless 2 in one pack, explains the 
difference in overlays , other than the POD number , also different datecodes on each, but would require 
6 pins each then, 4 hidden.
Will power up on the bench and then remove all those screws to explore the hidden side of the board 
Looks as though those black lumps will remain a mystery,I powered up ps and pa and test feed passed 
through both ch. So unless an intermittant problem in the pa , problem is in the mixer part, along with 
absent phantom supply, so off with all that mixer hardware instead of all those pa screws 
Rear remove mesh + 2x plastic spacers
1 only fan working , stuck bearing but both are bad so replace both.
Sp outlets trace thru to zobels
op devices DVM-D test ok
sheered off pot spindle , as per tips file
mixer umbilical
5,0,0,11.8,15,-15,48,0,0,0,0,low,low

Phonic DM2010, 1997
LB1482,7912,7812,7805
each ch for line input, Rt ip signal , nothing on left with buzz of constant pitch 
on headphone op.
Intermodulation of  mains and tr signal of 400 Hz and also 180 degree out of phase

Phonic Power Pod 1062,mixer amp, from 2002
In for switch replacement but owner says he has , sometime back , got a
shock off the mains lead by touching the earth pin when just unplugged from
the mains.
The large conventional type mains transformer is mounted on a metal plate
that is held to the wood of the casing by 4 bolts. There is no earth strap ,
or ever has been , to this plate or transformer frame, so not earthed. The 4
bolts are exposed through casing on  base of the amp. 
240V , UK use.
There is just the input ground wire to the plate housing the mains fuse
holder. There is no specific bond wire to the main PA just relying on metal
brackets/spacers and self-tap screws "bonding" back to the inlet plate.
There is a yellow cased X1 .47uF , 330 V  neutral and live on the flex 
side of the mains switch .
So what class of electric shock do you call that, high impedance , DC , of
little medical consequence in itself, but surprise effect could have
indirect consequences.
The switch was tiny 2pole 3 way mode switch at an edge 
position just where someone put their thumb and pushed it 
in , disturbing switch action and crackling on one channel.
While in there to replace that switch , beefed up one 
of the most used 1/4" input sockets as per tips files.
pa uses 2SA3264 , 2SA1295
2x10, 4x 0.1R
n/c th sw, MJE340
On reassembly (master controls side first in ) if 
peak LEDs light then put the 1/4" bush nuts back 
in place for ground continuity, so if loose in use 
could cause this symptom with no input signal
load test with 400Hz, to give 8V ac over 4R 
for one channel (B) only 
9 degrees C over ambient after 15 minutes.
Fan on full after 10 minutes. 8V increased 
probably but difficult to tell with change 
of fan consumption affecting readings.
2 3/4" x 7 1/4 al plate , midway, over the top of heatsink 
and under top of case ,  
1/2 protruding to take thermometer.
Designed for air gap under the amp for this test

Phonic SE710 speaker, intermittant
bad spade ,tighten horn sc, for the mesh, the ms sc is at centre

Prosound 400 ,2003
about half power on ch 1 compared to ch2
4x 2sa1941, airpax 67F, 065 the sensor, 2x D2061, 2x B1369, 2x c5198
2x 15K,2x10R,D669A, 2xB649A, 2x D669A
Physically broken fan spindle  just rattling not turning
Bit of a mystery as main tr are h/s complementwise , half on top 
and half on bottom with a bit of case cooling. If split ch1 top and ch2 
bottom I could see gain reduction coming in.
Top line of TOP3 C to Gnd , diode test .51V
400Hz in with mid level pot, each ch, over 8R, .39V ac o/p
+/-56V ps, 9V on fuses, 1.3V on th sensor
17V no load fan supply and 16V with 2.6 W,12V fan 

Prosound Minimix8 , Maplin, 2003
compact 8 channel mixer
Loud crackling on left channel
With twizzle stick located to a 36K 1206 format SM resistor, 
failed bond to one of the lands, replaced with 39K as to hand.
overlay Number not noted.
ps normal 2 amber LEDs on
15R,2W, C2383 ? TO92 device
.9(45V on phantom), 0,0,-,-,5,0,-17,0,17 on ribbon
7805,7915,7815,D2061 ?
The main pcb cannot have passed visual inspection test
as something in the wave solder m/c must have wiped 
down a strip of the board, smearing bits of solder with 
it. Cleared away the most potential problem lumps.

Quadratec VS450 slave amp,1996
4x 10N16, 4x 10P16, 4700uF  80V caps
1/4 spade connector of CT secondary only held in place 
by short leads and so half-loops of wire from Tx
Clipping monitor 1N4001 40V zener, 330R and LED

Randall RG100G3 powerFET amp
"no name", not Hitachi ,2Sk1058 failed in low power practise use. Securing
screw to h/s was fine . Known problem of Randall using suspect devices?
probably 2006 PbF/RoHS labels
More evidence of dodgey sourcing. The mounting hole is visibly off-centre
relative to the hole in the flange, displaced vertically.
Looking under x30 one of the 3 injection casting vent holes has this "ident"
impressed in the 1.3mm diameter recess
MALAYSIA
AG
8
also a presumed date code of  6F1 marked under the K1058 for th earchives,
but no maker name or logo
This was D-S short failure
Off centre hole is 0.3mm displaced vertically. No first rank manufacturer
would have that amount of engineering departure from the industry TOP3
dimensions
I could not read the device number on the only other transistor on the pa
board. Required my PTFE magic trick to read it. Will add a bit of heatsink
to this TO220  .
TR7 on overlay
marked
TRF820
TR 542P
7D
and 83 impressed in the casting vent hole plastic
again no logo or makers name
no data found in wwwland
"passing off " as  IRF820 ?
its not a bipolar transistor, the T of TRF is about the only readable letter
without PTFE, so not an I.
Back working again replacing the TRF820 and 2SK1058 principally. I would not
have expected to see just 1Kohm separating the gate of  an FET from the
anode of a valve.
One 10/32 UNF captive nut graunched replaced with 4mm captive nut and bolt. 
One celestion seventy 80 , G12-P-80 measured 11.8R . together 5.9R
As found at 30 percent mains drawing 1 amp but mains fuse not blown. 
Disconnected QC13 and 14 and mains Tx seemed ok. 
Fix a chain of cable ties around the H/S and pcb for handling. 
IRF740 for the TO220 and joggle leaded 2SK412 for the 1058
2xK1058, 2x J162
2x 072, 5532, 074
4x .1R 5W, 10R 5W
2W 10K,100,100K, 100, 2x100K
2x 4k7, TRF820
ps TIP120 , 4K7
with 130V mains 
190V, -30,30V
Tank 2BB2B in cct, 28R, 201R
Tx R
1.4.. 2.5R R-R, 2.5 R-Bk-R , .7R Be-Be
With 130V mains
op DC .5,0,30.6
-.1, 0, -30.7
IRF740 160, 181, 113 DC
Check wiring is not fouling the tank
93mV 400Hz clean ch all pots mid, no boost
4.4V over 8R


Rat, foot 3 pedal 
Could have been made anytime from the late 1970s going 
by the home-made feel of construction and basic 
plotter artwork.
Broken foot , then broken plastic battery enclosure 
screw , sort of held in place with gaffer tape 
but every time the switch was depressed , then trapped 
wires between 3PDT sw and batter case shorted against 
sw pins. Used 100K log pots and OP07DP

ReverbaMate, Sole Mate , spring reverb, 2010
Brand new out of the box and the footswitch is broken. Owner wants me to
replace the switch rather than returning to the importers for a replacement.
While in there try and sort out what apparently is an age-old problem with
such external reverb boxes. Set guitar , amp and reverb for clean and then
excess gain when changing to "dirty" ch. He does not use the second footsw
so I'm thinking of using that to switch in a preset over some gain setting
part of the cct 
Existing user pots are output level and dwell but not mix.
Sw marked with logo YIS in a diamond on one side and RoHS on the other - say
no more. Will have to break into this sw to see what this new to me,
presumably generic, RoHS problem is.
Probably a generic failing of "X wing" format of  footswitch rather than
RoHS. Because of the X format the contact surface to the tipping contact is
a point rather than a line so it punctures through the silver? plating of
the tipping contact, into ther base metal. Then an irregular surface to trap
contamination etc inside the pit .     Regular format like standard toggle
sw would have the fixed contacts appearing as a line because orthogonal to
the casing rather than 45 degree set.
By X wing I mean this external appearance
http://t3.gstatic.com/images?q=tbn:OPXHa_CHLpMgiM:
rather than
http://t2.gstatic.com/images?q=tbn:jrpyuMl8iMi8tM:
For anyone else coming across these variants - WUT Pat No 168524 proudly
embossed on the side.
13.9V ac giving +/- 9.3V
Main sw wiring starting from N/c going round
N/C R, LED to Gn / Cap to W, screened W, screened R + cap
.26V p-p 400Hz in , mid dwell and level
4V at pin1 and .58V at p7, .16V over47K at o/p as p-p on scope
p1 2V min dwell 15V clipped at max dwell, small board 5532 ok , main board 741 distorts
Tank in some other input setting , black 1.5V p-p and .1V on red p-p, send about 200R and receive about 73R, 
3 springs 
22K R at springline return put 4.7K in parallel to it 
8R phones loads the o/p too much for monitoring
Over 20K dwell pot added parallel  2K seriesed  2K preset 
4 x CD optical block elastomer decouplers added under tank thriugh 4 cut edge slots, with 3mm bolts through 
with TO3 nylon washer padding to the screw cups. Nuts just tightened and then welll lacquered. 
Ground point added to tank from I/P ground point. And ground connection between both pcb and chassis.
Owner never returned so shifting gain from send to receive plus mechanical decoupling must have 
worked. Carpet under if more decoupling required.

Italian RCF Flexa PS6320 modular amp system, 2006
MF6000, PS6320, 5x UP6081
Remove top cover to remove modules
LM393
UC28025DW, Vcc p15, 
ULN2004A
MC34152
ptc to R21 and U18, maybe NTC below 15 deg C
4538 p4 to opt1
C1 supply from small Tx supplies p8 of U18
to probe first smps and control board, turn upside down and fix with spacers 
to the other end of the module
remove6+1 large sc of large H/S plate
Just the thermal LED shows , also with all 5 amp modules unplugged from the rack. Nothing looks bad , driver 
transistors and rectifiers, large Rs and caps sloppy-test cold ok , fuses ok , etc.
12V on C10, 266V on C22
12.3V on C13
D25 wrt gnd not DC, heavy mains /15mS signal
gated HF on D3 
place 47uF,25V over C15, brings supply up from 8.6V to 9.5V 
but still LF modulation on it
12.6V viper p1 to p4 supply  cut through main trace
From D25 and 15V dc but still 3V 5mS sawtoothwaveform and bursts
.9V on FB wrt p1
1.1V on hot side of OPT1
1.6-1.7V on cold side
18R in Tx supply line
FB set by 47K and diode not via OPT1
D21 with 47K zener topcode H2P , measures 11.3V at 3.3mA on testing
Looks like the ST VIPer 12A , SMPS driver IC, data out there, powers a donkey engine SMPS then the main when the cold side control logic says ok to do so. I assume a schematic is not out there anywhere 
traces and ribbons from PTC thermistor on the main SMPS Tx are ok to the control logic. I don't evenknow whether the ps will run with no working PAs plugged into the power bus. Next thing to trace , before probing out reduced-hot 
All the chippery, I've found datasheets for, so maybe resolvable without schematic. What I thought was a uC (with buried FW of course) is a crystal controlled second SMPS controller for the main ps, and control logic is hardwired as CMOS 4000 and opamps
First small SMPS is in burst mode, presumably thermal shutdown (falsely or validly not determined yet), and cycling to restart every 30mS, so reduced supply voltage with nasty sawtooth superimposed. At least Viper 12A are easily available, hoping not due to shorted turns on the small inverter Tx  
Replaced the primary SMPS IC and same poor DC supply .
Determined it was not due to excessive load, shorted turns in the inverter Tx unlikely.
Tried the secondary SMPS powered from bench ps and that brought up the internal Vref , requiring a supply of 10V , not 8.6V which is just below the undervoltage lock out. The Vref supplies the "thermal" LED opamps etc.
Went back to the first SMPS and placed 4.7uF across the little 2.2uF SMD aluminium electrolytic that smoothed the sense voltage and the DC supply came up to 13.2V. So bad ESR cap again it looks like, falsely telling the IC that the Tx was overloading, rectified sense voltage was too high. The opto coupler was not for the primary SMPS, coupling is the other way round, probably to pass mains AC-ON confirmation, to lock out the 24V DC option, not used , as only mains use .
Trace cut points p5 and p7 of U8
second SMPS driver 7 deg C over ambient
cut trace near R33, cut supply toU7, not U10
cutt race near U6 , p13
Bench ps 10.0V on Vc and Vcc then 9.75V on V (C14)
5V ref comes on and supply to U5, Red LEDs both flick on then both off, Gn and Y LEDs off
Replaced Viper and same sawtooth
Placed 4.7uF over sense rectifier cap and 12.5V on Vc/Vcc and no sawooth
replaced with 2x 1uF 100V , remade cut traces and removed 18R in Tx primary line.
Will tidy up cut traces and should hopefully be back into operation. About 2,500 GBP amp and as a not current model and long wire HV ducted cabling and transformered speakers etc, perhaps that again if a replacement 5 ch distribution amplifier was not compatible and all the other kit had to be replaced also 
13.2,5.1V, 10.4V on 10uF
Y LED comes on , reconnect 2 x drive out lines to other board and Yellow on, green on when switched on and after .5 seconds, no red LED
Yellow = AC mode and Gn = on
Failed electro 
452
2R2
50E 800 ohm ESR, 0.05uF 1KHz
Y is standby , Gn is full on
continuous 10V 8uS pulsesfrom both o/p of  driver to large Tx main smps
in full on state no increase in 12.3V and 5.1 V power rails on the control board
refitted in rack
1 UP6081 in place ,slot 7
sw on and peak and overload LEDs flicker with open input
With mid pos bass,mid and treb pots, and volume advanced peak LED comes on
Slot1 , measured DC, from J1
0,23,-23,0,n/c, 65,43,26V
low ,-26,-43,-65
with 5 amps in place about 0.5 amp mains draw
25 ohm in series with test speaker , mid controls and touching the input, hiss but no hash
single .1V 400Hz unbalanced in one ch
5 on vol ., 1V over 33R of test load
1V in 400Hz, 8.6V ac over 33R
red and gn LEds on , red dips about 2 per secondbut o/p ok
vertical line of TO220 , quiescent , 25 deg C over ambient each amp module
and ove rdiodes marked PK MUR?? , 20 deg C over ambient
with amp ventilation sealed off under the rack , and no cover, 
main H/S 15 deg C over ambient.
Bounced back a month later. AC yellow and thermal lamp 
flashing about 0.7sec. A heartbeat thump on the speakers 
and amps looking like xmas tree lights with all LEDs flashing 
alternate overload, then Gn + red peak and signal.
Then next power up ps leds flashing only.
Same with the ps removed from the rack. 
Bad HV cap,C22, 205V only, bulging under the body.
SMPS1 o/p dipping from 13V to 10V at a slower rate than the LEDs
Disconnect J3 and stable 13V but then thermal LED on
Jumpered 400V 10uF to C22 and ps runs properly and 307V 
stable on it.
Replaced C22 which was 1uF 450V 85 deg C with 2.8uF,400V 120deg C from a CFL, 306V Y+Gn, 310V Y only with J3 reconnected

Roland Cube 15X, 2008, PbF
Gradually lost volume and distortion in treble. 
No problem found with me, redid usual suspect solder. 
Replaced input so. , Gnd, T, T-sw, and reinforced the o/p so. Jalco, prize off white rear section and 
slab of silicone rubber slid in each side, 2x 1.8x5x15mm , add glue to reinforce the 2
small closure tangs. Yhr innermost pair of contacts is the speaker switch
TDA5020, 120,1.0R, 2x10R
Earthing bolt needed molegrips on the head to undo . 
Power switch uses contacts in reduced power setting so not a problem source.
With ground tag removed and powering then high level ultrasonic oscillation. 

Roland Cube 30 Bass , maybe 2003
The box had been squashed and distorted in the hold of a plane.
A year later, reported as fuzzy sound on the bass  E string 
even at relatively low levels
but otherwise fine sound rendition or backing off the bass control .
Feeding a signal generator in then indeed a distinctly fluttery distortion
in the range 50 to 70 Hz on top of the wanted output, ok above or below that
range.
No external speaker output on this cube and before getting inside to scope
it or run an external speaker I took the front grille of in case of
parasitic rattling but no change. But putting a sock in the front/back vent
tube in the speaker surround cured it.
No problems with the reservoir cap solderings
Decoupling the negative black lead (not ground) via a 10u polyester cap to
the scope ground the electronic trace was fine at all frequencies and
powers. Semi-permanently blocked off the reflex/bass port or whatever that
hole is called and the intrusive 50 to 70 Hz induced flutter has gone. Just
the normal low level flutter , for low frequency, high power output due to
vortexing/cavitation or whatever the normal distortion due to bulk shifting
of air mass by a cone is called.
Blocked off the vent with a jam jar lid filled 
with hot melt glue and also introduced 4 plastic 
sleeves over the front grille retainer screws to 
push the front grille further away from 
the speaker.
Some tech details 2x TDA2050
270R, 2x 220,47, 2x .68 1/2W,
12.7,0,12.7V ac supply
10 inch , 8 ohm speaker
IC5 to red speaker lead
IC6 to black speaker lead, complementary fashion, 
not ground.
+,-,0 monitor points on the 1W Rs
270R is across the -ve rail cap
IC12 reg ? has 11V , 3.3V 
When out of the casing the 2 earth bolted leads need tying 
together for amp to function.
To monitor the speaker on DC isolated scope I bridged 
the introduces chock blocj connector with a C rather than an R 
to connect croc clips to. Although only 15nF this produced 
high f oscillation of 1.5MHz of a few volts so may be susceptible 
to stray cap. After all that the owner reported the 
same problem with another amp - the E string 
problem was with the Ashworth of Truro acoustic bass 
bridge transducer.
Sound colouration setting on Roland Cube 30
How the output looks, on an oscilloscope, for a
regular sine shape waveform from a signal generator as an input 
and using the "octave bass" option
 Octave Bass shape 
for various frequencies.
Because of image capture/strobe problem I've coloured in part of the missing
60 Hz shape in the top image.
The missing bits on the 160 Hz image are there but feint
Above 300 Hz the distortion disappears.
No distortion, as such other than level change, for these bass frequencies when any of the other sound shape
options are selected.
Looks as though the definition of "Octave bass" is it adds a subharmonic one
octave below the note in question.
Graphing out on a pc the sum of 2 sines of differing relative
amplitude and phase and fixed octave apart produces those shapes.
Just as well I keep repair records as I met this amp 5 years ago with the
same untraceable fault. Owner and me had forgotten it re-appeared when he
used the bass with a different bass amp.
Previously reported as a fuzzy sound when he used the bass E string. This
time just playing the F on the bass E string , a rattly buzz, like a spiral
wound guitar string vibrating against a fret and loss of the actual F note.
I've not seen the bass or transducer , assuming its a piezo element - make
Ashworth transducers, what could cause this symptom, disappearing for 4
years? Both bass and amp have been around the world a few times on cruise
ships so perhaps excessive heat or humidity
It looks as though it was due to owner sticking a bit of plastic tape
between transducer and the body of the bass, to stop the bridge moving - so
much for electronic repair
I gave him a rubbber doorstop, for acoustic decoupling, to place under the spike , worth a try, 
if it is a feedback problem.
Without differential scope amplifier/probe, audio out is missing something
in the bass range about 70-80 Hz. Line-out signal faithfully follows the
bass guitar input signal . Shure microphone, capable of those frequencies,
monitoring the sound from the speaker, does not match the input at those
sort of frequencies. But is it a failing of suspension or something of the
speaker or some inductive/capacitive interaction with the amplifier when
loaded  with the speaker?
Not yet monitored the main rails to see if dipping on this bass amp.
I will then be subbing the speaker, as a test, but it still would not
determine whether an amp or a speaker problem , speaker is original to the
combo. Any simple component to put in series or parallel with the speaker to
check if an output matching problem ?
Volume , tone controls etc are in the DSP sextion and as line out is fine ,
I assume not a problem in that piece of magic.
This is a Roland Cube Bass 30. There may be a faulty , going open, "shape"
switch and may sometime settle into the default at the bottom of the
resistor chain which is the Octave Bass setting which , may explain the odd
effect
I tried a solenoid but not enough output and poor at sub 100Hz. Do you know
what the response is like below 100Hz on your pass-thru Tx ?
reminder to buy one or 2 of these current Tx
http://ww.sourcingmap.co.uk/020a-input-current-epoxy-resin-embedding-precision-current-transformer-ta17-p-133281.html
Dug out a couple of microphone Tx and checked they worked down to 40Hz ,
taking readings, less response but not too much. Then some more important
jobs came in.
One for the phones out line ( so same f response) and one with series 1K or
so over the speaker, should work fed to a normal dual channel scope
I tried a couple of physically larger microphone Tx and the response is
essentially flat from 2Hz (the bottom limit of my sine gen ) and about 20KHz
, rapid tail-off after 30KHz.
So will try one or both of them when I get back to this speaker/PA problem.
RTFM time : the "shape" switch on a Roland cube 30 bass does not switch in
and
out the COSM selection, just changes the character. I think there was a problem in this sw and when the
wiper disconnects then the function stays with whatever was selected before,
the control lines stay high.
Incidently if o/c at switch on then disables the amp totally. The speaker/PA
is perhaps fine after all , but will try comparing at some point , to at
least see if microphone Txs are useful for this
ALPS switch , p1 and p10 common, p9 n/c ?
via 220R to ground p8 Concert, p2 Octave Bass
CN5 p8 GND, Red to  sw p2
Unlike the chain of Rs in the Cube 100 Bass this is separate control lines to +V and taken 
low for active.
Shape sw , line 4 of the ribbon
Removed the innard of the ALPS by prizing outwards the 4 metal tangs of the cover 
and desoldering while levering . The ball bearing stayed in place but fudge glued it in for reassembly.
Cleaned out the active surfaces and grease from the shaft and restressed the wipers.
Overcoming the heatsinking effect of the ground plane around the sw, the 220R dropped away unseen. 
Powering up then no amp function until fingering around the sw area took the line sensing low somewhere, 
for amp function but switch off and on then no function again. 
Then probably confused m/c sc with amp to cab sc, for refitting the speaker and different threads and ended up 
cross-threading a sc into the clinch-type nut fastening that proceeded to turn in the chipboard. 
Had to grind through the bolt to retrieve the sistuation. Tapped all 4 "nuts" with 4mm and changed 
all 4 sc , JIC.

Roland Cube 30x, 2008, PbF
Phones/rec out socket. It is implied in the user manual but can anyone
verify from experience, more exact details.
1/4 inch socket with 2 isolated switch actions (Jalco). For phones, ie
stereo plug, the speaker is fully muted, via control logic .
For rec out , mono plug (explicitly stated in the user manual)
The innermost "phones" switch does pass the speaker current, the outer one
goes via 1K to somewhere. So the mystery deepens.
Previous cube, different model "30 bass", triggering the outermost switch
only , by plastic rod inserted thru the sw , dropped the speaker volume to
10 percent or so of whatever the volume was set at.
Service manual on elektrotanya just describes the test function. Triggering
one phones socket sw, triggered in isolation,  cuts the speaker ; the other
,triggered in isolation, attenuates marginally from eg 1.58V ac over speaker
to 1.2 V . But in normal use , the speaker cut sw takes precedence and both
stereo and mono jacks cut the speaker.
Now I've replaced the socket, foreign object landed inside and then rear of
the Jalco got mangled and pushed out
Just 2x  mm-size plastic pawls hold the white rear in the black body. Maplin
and RS no longer stock them , I wonder why - I gave up hunting for uk
supplier. Standard 1/4 in stereo socket melded to 2 ultra-miniature spdt
microswitches is now in there, (ITF)  far more robust.
Grind out part of the passives pcb to allow for replacement so. 
If thick padding on bush then minimum amount of pcb needs cutting away to give space.
Mica glued over the pcb before fixing upside down so in place and wired 
over the edge to the rear solder points, not thru board.
Padding ring on bush of the function sw.
No function if bond points are not connected to chassis and all LEDs stay lit.
Jalco pinning , not always the same
1 sleeve, 2 tip , 3 ring
4-5 (and 6 in dpdt) one sw and 7-8 (9 with dpdt)
2x 2.5A fuse
33R, 2x 6R8, 390R, 2x 470R
IC6 2933, 2x TDA2050, IC7 7D 6Z, IC17 7812A, IC16 9R 79
IC5 JCPL, IC9 2100, IC10 4580, IC8 4580, IC2 4126 07H1
CN U1 connector empty
One phones sw takes the speaker current to red speaker wire (iiner sw)
Outer sw to 4x1K RA between IC3 and WP4 , then unknown , not traced
Check all ground points if low volume out

Roland Cube 30 Bass 
A sort of auto-wah effect at the flanger rate but with the effects controls
turned to off position. 
For working on these boards external to the casing , remove 
the heatsink and add a bit of flat metal to the TDAs temporary.
Looks like problems with the system of pots (nothing ohmically wrong) turning
to 0 ohm to switch off digital effects?, the LED goes out but it is as
though the micro doesn't know that.
Good sine signals through both sides of dual opamps IC1 and IC2, distorted
signal at both sides of same IC , IC3.
+/-8V supplies (2 TO92  near the main caps) to the opamps good and clean as is 3.3V rail for the
following.
Tracing signal back it seems to go to IC4 an AKM4552VT no data found but
AKM4550VT is an Asahi ADC/DAC of same 0.65mm format 16 pin but slightly
different  pinning.
Good sine in but distorted signal out so presumably the digital processing
is buggered somehow.
Tracing the lines back to the 48 pin IC8 Roland chip then pin 22 goes to the
LED and the wiper of the effects pot goes to pin 4 via 100R. 
Delay pot wiper goes to pin 5 of IC8, 3.3V on all pot end of tracks.
I don't
understand why with a few ohms left on the pot at "zero" the LED goes out
but the effect does not stop. presumably a drift in the 
IC8 internal sensing. Rather than trying to change the sub miniature
pot I added in a switch (thru front panel) to ground, via 50 ohm, 
on the pin4 side of the 100R, 
and 56 ohm over the existing 100 ohm, owner never uses the effects anyway.
Strung some stout silicone cord beween the 6 way 
switch ribbon connector and a cable clip clip around the board edge. 
Then some standoffs under to press both large 
SM devices in case it was poor soldering - nothing 
observed and could not make the problem return. 
If it bounces back then that 
will be the first task.

Roland Boss DR 55 drum machine, 1979
Just some 'top hat' noise but no drumming
The Vcc pin of the SRAM uPD5101 was corroded, no 
other pins anywhere on the board corroded.
Presumably something acidic left over from 
manufacture had corroded the part of this pin 
passing through the pcb.
'Vcc' should have been battery minus diode drop 
but was about 1.5 V less on this IC pin as coming from inside IC.

Roland Cube amp
The only freebie schematic for these sorts of amps I've found is for the 
Cube 100 bass to get an idea of  the series (TA2022 o/p device)

Roland Cube 
Bad volume control
Alps vol pot , 10K  linear playing up
replaced with standard miniature pot wired in reversed upside down 
and part of rear cover and paxolin cut back 

Roland Cube 30
No function including no LEDs.
Failed 3.3V VR, ominously tested  no load as 4V, maybe normal , will have to try some known gooders
About 1.5 ohm ground to 3.3V rail. Found where the confusing inner 3.3V plane came off (near IC9) cutting either side of there and a couple of other places, limited to one area of board.
Powering with V and A limited bench ps set for 3V limit, taking .2A, dropped .4V and .3A dropped .7V.
With IR thermometer I would have thought 0.2W would shine out , about 1 degree C only above, around IC4 and AKM 4552VT codec, Japanese datasheet out there. From that I think I know where to cut its supply trace, despite being under the IC.
Anyone been here before ?, the main Roland chips are dead cold.
Anyone know what 5 pin SC70-5 or SOT416 format IC top coded JAPN is, just in passing, googling got nowhere ?
Reminder to myself when using IR thermometer - use a distant LED torch to illuminate the board. Misled into "finding" a faulty main cap , as heating up a few degrees in one area of the cap, despite no normal connection to any 3V line. My flourescent lamp was reflecting heat off the cap top. Even turning off the lamp made no difference , retained heat of course.
Also handled a switch and 3 seconds later found a (phantom)  hot spot there.
No change in ohmage heating or freezing.
I don't fancy removing a 16p IC, where it is, even if a replacement was available, but now I've got this far I have to follow it through to the end 
The J of 4 letter code JAPN has 2 dots over .
My IR thermo has a conical reflector to the pyro, just the right size to test each of the couple of dozen radial electros, by placing end of cap in the cone, and no excess over ambient 
Isolated that IC and still low ohms load on 3.3V line. About all that was left to cut was area of the big BOSS chippery.
Cut line to p38 of 80 pin R02565501 and inside that was the low ohms, so end of the road I think. Perhaps a thin trace 3.3V or ground line runs under the AKM 16 pinner.
Perhaps I'll solder a wire to p38 and drive again with some less constrained current and see what happens with IR monitoring, for edification. First Cube Roland main chip failure like this I've come across, 2 stomp boxes before IIRC 
Applying bench ps to pin 38 isolated from all else, then for .2A, 1.3V dropped and 10 deg C rise of the chip. 
before consigning to the mule park , investigated the JAPN IC a bit
5 pin,
p1&2 gnd, 3 N/C unless hidden in an interlayer,4 to large Boss R03015201  p21, p5 absent, p6 3.3V
Power-on reset IC? 
 IC is S80130ANMC.   Voltage supervisor with built in delay
I've never seen such long timed power-up reset/delay IC before.
I suppose one dot is the index mark and the other dot Seiko logo. Another SMD topcode out there now. 
UPC2933HB 3.3V,1A ?

Roland Cube - 30 Bass, CB30 2004?
loss of mains sometimes, waggling mains lead would bring it back
N225 "sign of the devil"
Cut first cable tie at its latch to get space to cut the other ties without damage to cables
Stagger cut the sp wiires and add choc block conn
Mains sw replaced as one terminal was loose and cut out a hole in the back plate for 
an IEC socket rather than original fixed lead. Need to remove Tx and mount the 
IEC over the original entry hole and in a vertical sense

Roland Cube 60 ,2006
sp 6.8R
Intermittant drop of ound , kick cab will return it
4sc each side of cab, unplug sp leads
o/p so Jalco , reinforced as detailed elsewhere, easily removed .
Dental hook between white and black at So rear to separate, as limited ability to remove, header in the way
O/P solder pads with bush towards you , no plug insewrted, LH pair closed and to gns, RH 
pair closed and isolated from gnd
sp hiss with bare jack pushed in the socket
bad i/p so, not so easy to remove. 
S, T and T-sw , contacts for replacement , tinned wire to subboard and that hotmelted to main board as 
no anti-turn on the replacement
Tried "long snips" lino blade tool but still not enough 
wire length. Remove 4sc of Tx, one needs heating to remove, 
beware glued felt under the Tx. Remove mains fuse board

Roland Cube , intermittant low volume
Speaker Bosssp1 8R , CHINAI.S.T 138K measured 6.1R, 6.8R tweeter. 
Recording out diverter switches. The one at cab side drops the speaker 
volume if  activated/loose. Other one cuts the speaer, both via control , 
not carrying speaker current. Both about 18 to 20mm inside from the lip of the mounting boss. 
Measuring activation force 330gm (spring balance or light spring lengthening measured and 
transfered to weighted kitchen scales) at 20mm from end on 140mm long 4mm 
plastic dowel held at the other end, held so the rod is diagonal across the 1/4 inch hole. 
450 gram for the full cut out one.
Avoiding dismantling whole amp.
Dremmel disc cut into the black plastic at rear top of socket , right on the axial edge as that is 
where the switch action is, cab side . About half the rearmost length. Push some silicone 
sleeving into the gap to tension up the spring closure action . Brought closure force 
on measuring from the front to about 600 gm.
One of the speaker connections was poor also.
Roland cube , tweeter over the 10 inch bass unit. Stands on what seems to be
a plastic stem passing through the bass cone, wires to it passing through
that cone also. How to remove the tweeter section to get to ,hopefully,
failing wiring joint that is normally covered by the dome of a single normal
speaker. There is a square recess in that stem, a "Frenchman" to break a
plastic weld joint ? no fixings proper seen anywhere.

Roland DB500,1999
cuts out sometimes to very feint, sometimes dips in volume, sometimes goes hollow ie 
lack of middle sound.
Sp 5.5 but easily varied when tugging on the red/black sp wires and a rattling noise coming 
from inside. The rivet for the tag board at the basket had pulled through the fibre board, 
flapping around with bare tinsel wires able to cross over , and a line etched/scratched in the enamel of the basket. 
So tugging on the wires was tugging on the cone itself and varying the DVM-R reading.
Bad low input socket bypass sw so affecting the signal into the high ip .
low ip S/T/Ts
high S/R/T/Ts
sp SPEAK00020 121919 G1 8 ohm 67-99 450250
Earliest example of PbF ?
Previous earliest I've personally come  across was a Yamaha RS7000 sequencer, 2001 ,
too early to  mention the likes of RoHS or PbF etc anywhere on that.
This time a Roland DB500 from 1999, the solder joints hazing over if you  admix with leaded solder. Or is it some other solder formulation that can give a PbF+SnPb solder sudden-cooling + hazing appearance?
I know it all started coming in , in Japan firstly.Japan passed the Electric Appliance Recycling Law, April 2001.
And the soldering on every aspect of Sony's DCR-TRV 30 digital camcorder,
released in March 2001, is "99.7% lead-free, including all supplied accessories". 
Anyone know what the Tick N225 compliance mark means, again on the back of an amp with dodgey solder.
Latest component datecode 9940 and a pcb "7 segment" overlay date of 9945 
I assume the circuit boards were populated+soldered in Japan, although only reference to designed by Roland Corp USA on the rear of the Amp 

Roland DB500 fell on its back
phones o/p ok and DSP ok
Insulated phones so, Ring sw contact broke away (see elsewhere here)
This time moving contact grind back either side of the V central section of the contactto take 2x 
thickness of heatshrink sleeve to give insulation from insertion of the jack

Roland DB 500 bass amp , 1999
Sometimes cuts out leaving hiss through amp , returns by knocking the 
heatsink. Remains trouble free for some hours and then 
returns. Likely symptomatic of bypass sw in a 1/4 in socket, 
corrosion / grime thin enough and spring action enough to break 
through upon knocking metalwork..
If phones socket then no relay click over and no hiss in PA. 
If hiss on pa then "return" sw problem.
suspicious solder on 5V reg pcb on h/s
Is there any redeeming feature about working on this amp?
I don't suppose removing the front would reveal removeable connections on
the speakers.
So you have to remove a choke, ferrite filter, numerous earth straps etc to
be able even half get at the main board. Then desolder the 4 speaker wires
 i see a choc block going in there). 
assembled in USA, otherwise Taiwan .
CHIA YU is probably the make on this one and the choke as well
But its the stink of horse manure
inside that is most annoying. What do they make transformer lacquer from in
the USA? . This is the third such box , and all USA made, take the covers of
and the room smells of manure. Not the fresh stuff but the rotted form ,
caproic acid coming off it according to my chemist friend, or maybe butyric
acid.
other littoral stinkers were
Fender Pro 185, 1989
JBL SA660 (James B Lansing ), domestic amp 1969
maybe (precursor to?) this form of varnish
http://www.patentstorm.us/patents/5225468/description.html
This invention relates to polymeric insulation compositions which are
crosslinked to produce heat resistant and flame resistant products useful
for coating wire and cable products. More particularly, the invention
relates to crosslinkable flame retardant ethylene-vinyl ester and
ethylenealkyl acrylate copolymer insulation compositions which do not
tarnish the surface of copper conductors upon curing.
/
THE PROCESSING ADDITIVE
While any known processing agent can be employed, fatty acids or fatty acid
derivatives, polymeric processing resins and hydrocarbon oils, or
combinations thereof, are most generally used. The fatty acid derivatives
can include metal soaps, esters, ester-soaps, amides, and the like.
The term fatty acid as employed herein, refers to aliphatic carboxylic acids
having from 8 to 22 carbon atoms. While these acids are usually derived from
natural sources, they can also be synthetically produced. The fatty acids
can be branched or straight-chain, saturated or unsaturated and they may
consist of a single acid, or as is more commonly the case, a mixture of
acids within the specified carbon content range. Illustrative fatty acids
include caproic acid, caprylic acid, capric acid, lauric acid, myristic
acid, myristoleic acid, palmitic acid, palmitoleic acid, stearic acid,
isostearic acid, oleic acid, linoleic acid, eleostearic acid, behenic acid,
erucic acid and the like. Useful fatty acid mixtures are obtained from
triglycerides present in natural fats and oils including coconut oil,
cottonseed oil, linseed oil, palm oil, soy oil, tall oil, safflower oil,
corn oil, rapeseed oil, tallow or the like. /
This time yes but I doubt a JBL SA660 (James B Lansing ) 1969 amp would have
had a Chinese transformer inside. Is it a specification thing? I don't know
how many hundreds of amps made in or made for UK I've poked around inside
of, but none with the smell of rotted horse manure (not as unpleasant as
fresh manure smell BTW). So probability-wise looks either a USA thing or  UK
air polution or 240V operation combining with exotic materials
I should say it is not just me, this one and the JBL previously confirmed my
smell diagnosis, by 2 seoparate people other than myself. The JBL really
stunk out the room , not just while it was around but for some days
afterwards.
I can find no www reference to USA based repairers ever noticing this
agriultural smell, making it all very odd. Do they use another word for
horse manure over there?
No point in replacing like for like the 1/4 inch Jalco 1/4 inch 
sockets (see tips files for work around) 
Jalso A with pis marked 1 8745 9326 with 2 isolated sw
Jalco H 1(gnd) 4(sw) 32 (tip)
Phones one had to fit right way up and tags bent up and wires 
through a hole drilled in the pcb.
Had to cut away a bit of the digital board to make space for the phones one. 
Needs one isolated sw action as -14V (to 5218A -rail) used for switching of relay so 
use the fixed contact for that one.
22R to tip and 22R to ring from feed line.
Red and black speaker wires 5R , brown and orange 6.2R
Tr 4.8R// .7R (R-B-R) .7R,.7R
-ve rail pass transistor 2SB1642 , + rail pass tr 2SD2531
also 2SC3858 , 2SA1494
10R,.33,100R,+ 3x 5W unseen values
2x 5218A mitsubishi
2SC3381, 2SA1349
74HC4051, 2x 2SA1837, 2x 2SC4793

Roland micro cube, 2006,
9x8 x 6.5 inches excludes the handle 
Bad input connection, unless forced in one direction, 
not 2 years old.
How to get into the box? the bigger ones are easy in comparison.
Such a litle thing putting up such a fight. I've removed the speaker to have
a look inside and all I can assume is that it is just very strong metal/wood
glue locking the top panel part into the woodwork. The rear section is loose
of this L section panel but locked in place by the top section.
Its that double sided glued foam stuff, large areas of it around the 3 sides
of the top section. 
Eventually gained enough confidence to push a blade into the 3 to prize
apart, remove all 3 plastic pieces before any forcing.
post mortem on the Jalco 1/4 inch socket
No obvious problem but for minimal metal and plastic content and makes a
nasty scratchy/clicky noise on turning a jack plug in there, probably
because the tip contact is along the axis of the plug rather than across.
I suspect it was failure to positively disengage the grounding contact as
only something like paper thickness separation with the plug in place. I
could not induce the problem as found and had to take word of owner that he
had to bend the plug one way to make a contact.
Replaced with a chassis socket wired into the pcb
A 16 pin SMD IC with no heatsinking and drives a 4 ohm speaker of about 8
watts probably.
Markings,
TI logo
200001
67K
CC8C
Nothing found on TI etc but probably D class IC

Roland FP2 electric piano, 2004 ? , not PbF probably
No R speaker nor R line out, L &R phones out seem ok, as does the speakers
on/off sw. Amp hiss from the R speaker only, L is fine.
I got inside this 7 octave thing without breaking any foil ribbons. The
phones input socket switches seem ok, so does the line out sockets. But the
Line-In Left/ Mono input has a bad bypass switch. Although it is in a
position that would suggest a Ring contact it seems to be a tip contact
switch, difficult to trace the local traces as vias etc.
Anyone know if the problem there would cause the loss of one channel. As
difficult to "bench test" this sort of item, any other areas to look at
before some sort of reassembly?
I've only run it so far without the keyboard half connected, next time I
come across one I will try external input feeds L & R before dismantling.
These line in/outs seem to be simple mono so. with tip sw, no ring contacts
for sensing of R-S connection of a mono jack.
The "switching" logic seems to be if In-L/Mono tip is no longer grounded
then feed that signal to both L & R amps ; if you feed a signal in the R as
well and so its tip also is no longer grounded then defeat the signal from
L-in going to the R ch , and allow the R signal to R amp. Or something like
that, I still don't see why failed tip sw and no signal in there, would
defeat the keyboard output to the R amp.
The phones outputs were only operating as 2 mono outputs, now 2 stereo
outputs from L&R ext inputs . Hopefully that tip sw failure was the cause .
I suppose regular repairers of Roland and Yamaha pianos etc have long frames
that can hold, open, both halves safely while powered up , plus ribbon
extenders.
No change, same loss of one speaker. I'll have to look out for some sort of
basic midi keyboard for the next time, not one of my current bits of test
kit.
No convenient overlay marking of L-out/R-out on the main processor board or
on the PA board. I don't suppose that info of which header/pins those
signals should be on, is out there somewhere. I've found some long P-K bolts
and with spacers should be able to fix the 2 body halves adjascent and 180
degrees apart , and work on powered up , to at least find where those audio
signals lay. This keyboard has been dropped it would seem , stoving in part
of the base chipboard , up against where the ribbons connect to the keyboard
but as the keyboard works as such, then that local area was unaffected , I'm
assuming.
Then hopefully couple some test signals in there without the keyboard
connected
I decided that lash-up too whisky. The digital seems quite well separated
from the analogue on the PA board and 2 lines seem to come from off board to
p2 and p6 of an M5218 dual op-amp SIP via electros from CN1 p6 and p8.
Injecting 0.1V in those points carried through to both the speakers. That
CN1 header traces back to the display board with vol and balance pots on it
so a job for tomorrow
I'll know for next time, zero in to the pot to confirm PA or digital board problem.
Low profile 7 pin ALPS 103B 502C pot, I could get tending to 0 fully CW and
CCW pins 2,4,6 but not another triplet of pins. I did not realise these were
bass compensation? centre tapped dual 10K pot tracks
p2,4,6 one pot with 5K mid tap p1
p2,3,5 mid tap p7
and p2 common to both tracks
presuambly compacted grease lifting the flimsy wiper, from getting inside.
The track immediately around the spindle is conductive circle of p3 wiper so nearest the spindle grease.
Hopefully that was the problem rather than me not realising these were non
standard pots.
Will try tracing the p6/p5 upstream signal side back to the main processor
board or wherever for non-kbd  testing purposes
Back working again. Pin 5 and 6 of the vol pot is a good test point. They
trace back via electros to p1&3 of CN1 jumpered via 0ohm Rs to CN4 p10&12 of
the large ribbon and pinning back to CN13 of the main processor board .
Now to find something to cover over the hole in the chipboard and replace
all the screws etc
At least Roland FP. are not as heavy and awkward to handle as Yamaha P..
3 long pk at either end and 7 under front edge to separate the 2 halves of the unit.
With a dumpy crosshead driver handy I removed the 4 sc for the 1 in 2 out ribbon 
interconnect board as could not see how to remove the ribbon clamps. Probably would do the 
same again , to give more room to manoevre but with clamps still in place. Swing the full 
end of the clamp in ribbon-lengthwise sense to unclip the hook edge .
LA4708 main PA hybrid.
PA pcb 2x pk at the midi so. chromed m/c sc at earth point
24A05, BA3823LS, BA07T
JRC 2374AD, M5128AL, M5216L, RSC1= .24R
on reverse HC04 , 3x 4570, 
only 1 way of the sp sw is used of the 4 so makes it look as though there is a problem there for 2 ch
As non standard pinning and low profile 4 sockets, logo 6 flecks in a ring, 
decided to reinforce the closure force of the existing and cleaning. 
3 holes through the pcb, immediately outside and into the extended pad of the paired tip 
terminals , no multilayer board problem. 
18 inches of silicone sleeving anchored at the large diode and then a bead over each tip sw and 
round the panel boss to the next x3 and stretched and tied off and glued knot.
R10,R11 , 10R on the display board , 2x C4570

Roland RD300SX electric piano of 2004,
incidently very different from the RD300S on
http://www.synfo.nl/servicemanuals
otherwise SM not found
Meddling owner got inside to fix "scratchy" control.
Removed all the under screws and then refitted mixing up PK and machine screws. Probably wrenched the 2 foil ribbons on taking the casing apart and then trapped a ribbon between a keyboard pylon and grounded aluminium foiled base chipboard. Intermittant loss of notes in the second octave. By the time I got inside , changed decay setting to maximum, and holding notes in that octave, no loss of any notes moving the cables, presumably as I wasn't in full flow and playing big heavy chords.
Luckily not a CD sled type ribbon, and plenty of space here for a fudge repair.
As one track on one edge only is damaged, as far as I can find , I'll try scraping back and mechanically bridging with cut-down phosphor bronze saddle from a small slide switch plus external clamping over that spot.
I would normally fully disrupt the break and take a piece of enamelled copper wire from pcb to pcb, perhaps with a pair of turned-pin DIL socket socket pins to make a breakable union. (rather loathe to take a soldering iron to the main processor board)
Anyone ever tried miniature rivets (good enough for pot construction), ?bridging with a piece of phosphor bronze strip from an analogue meter,say, plus mechanical clamping? woods metal low temp "soldering " over the break?
ie anyone  had success with some technique other than silver-loaded paint/car window heater-strip repair paint, which I don't think is reliable and don't use. 
Just in case anyone wishes to try similar.
Razorred back the blue lettering side of the ribbon either side of break, made more definite, so cannot intermittently remake after this bridging
Robbed slide contact from a new smallest size slide switch. Only a fine notch between contact faces, so stripped some seriously multistrand fine copper wire to loop into that notch. Twisted up and soldered off , to give some pretension to the contacts, ie to similar degree as the header contacts . Keep the excess wire in place to help sliding over the ribbon edge. Check for continuity. Swathe in hot-melt glue . Proof tested by checking continuity while locally bending, positive and negative, to about 30mm radius of curvature. Not that there is any bending, in use, just as some sort of integrity test.
More generally within the width of a ribbon , perhaps, make a hole between conductors, cut in half one of these switch contacts , place over bared trace, pass copper wire loop through the hole and twist up against tiny washer and solder off, cut off excess wire.
I wonder if anyone has tried "cigarette paper" spot-welding a bridge connection on a ribbon cable. A thin bridge strip clamped in place over a barred trace , with some thin cigarette paper , in between. Connect a high A, low V transformer (+diodes?) to it, with a current monitoring relay mains cut out.
Clamp up tighter until the current bridges the gap and forms some sort of spot weld. Repeat for the other contact. Would it fail in similar fashion to trying to solder to such ribbon traces? 
I would estimate the "insertion force" for sliding the 2 contact modified ex-switch contact over the edge of the ribbon was about 1/4 to 1/10 of the force required to insert the 22 way ribbon in its header, so similar or greater contact force for the "repair" .
Pin is neg for 9V 600mA supply. If less current ps is used 
display will come up a few sec , flickers and dies.
3sc at each end + 7 under rear, leave 8 under front edge excluding the one 
in the semicircircle cutaway, the inside clamp bracket.
Lay upside down and lift base up slowly to deal with ribbons.
Edit + write demo working , vol control ok
8 + 1ms under front, all the rest are pk.
Mark posistion of 3x keyboard feet on the aluminium foil before removing 3x top sc.
Line 1 of CN101, 16+22n ribbon lines = 38, 2x7+2x12 ?but plus 4 keys
line1 to common of D46,D47,48 and  31,32 of octave2
Refit central m/s of 3 of the keyboard to base then the end 2, 
turn over and fit all those pk.
Rest ends of top section upside down over a large book at each 
end , refit ribbons
refit 1 ms of bracket first and then the pk

Roland SH 09 , Synthesiser , 1981
New owner thought Ext I/P not working but 
only modulates interior oscillators when a key is pressed.
Remove rear + top metal section to get access.
Rennovated volume pot.
ps rails +15,0,-15V
Explored BA662 representative V dc
-14.3,0,0,0,-14.9,-1,-0.1,-0.02,+14.9
Maybe a pinned variant of BA6110 but the 6110 P/O 
in D.A.T.A books is patently wrong.
For BA662 looks like 
Pin 1 , control V ?
2  I/P with FB from buffer  O/P
3 i/p
4 Ground / Bias ?
5 -rail
6 opamp o/p to external FET
7 Buffer I/P from FET
8 Buffer O/P
9 + rail

Roland XP 60 , 5 octave keyboard , 1997
In for a power supply fault but while in there, the floppy drive has never
worked. Would it be a standard PC drive? or known simple repairable stock
fault? It does klunk once, on pwering up , sort of PC fashion
Standard PC 3.5 inch  FD in the xp 60 . Removing it and poking around and
refitting I can save to a 1.44M PC formatted disk and load back a "song" and read
as HEX files on a pc so perhaps stuck stepper spindle or connector problem.
I did not try an ex-PC FD in the Roland.
Noted the type as in the Roland as
Panasonic JU 257A 726P, not researched it, as the green FD front panel LED
was not lit before fiddling and did come on after fiddling and with it
return to function
I did notice 3 or 4 submin 2 or 3 way slide switches inside that Roland
Panasonic FDD, gives a goodly number of permutations
This one is back with its owner. The FDD would solenoid? click at power up
but no front LED, I assume a leads/connector problem unless a stuck spindle
could lead to lack of LED
PS problem 
some buttons illuminated but no display or output
Probably dropped as all solder points at the vregs (touching Vreg hs clamp 
would make good or bad) were bad esp the +15V
ribbons measure , when good
-15,-15, 0,0,15,15 (measured -1V when no display)
-15,-15, 0,0,15,15
0,0,0,0,5,5,5,5
0,0,5,5,
0,0,5,5
0,0,5
C4570HA (sil) JRC 5532D p4 and p8 for +/-15V or not, 5238A,4570, 5218A
AN7915F, AN7715F, P005RF21

Roland XP 60
loss of one note
Remove base, undo screws holding half full length pcb. Conductive rubber contacts on 
underside touch upperside traces of pcb. A1 to 2mm bug must have been in the wrong place at the 
wrong time , neatly squashed under one pad only was enough to silence the note. 
Cleaned all pads while in there with meths

Roland TR626 Drum machine
Intermittant power problems.
Beef up the soldering to the power inlet socket and glue with hot melt 
string to the pcb for mechanical strength.

Roland VR760 piano, 2003
Pushed in and broken solder joints on  dual 10K pot volume control and reverb vol control.
Need to remove bottom panel. Outputs board, dissolve the paint on the 
rear panel nuts (with paint remover gel) to remove main board 
with the flash reader. Mark all ZIF cables etc before removing. 
Remove the IEC board to remove the EQ panel.
ps voltages at main pcb are 15,0,-15,5.1,5.1,0,0

Roost Session Master , 1976
Failure of  output valves due to loss of  bias due to physically breaking
resistor. Also blown up dual concentric can capacitor for HT3 and HT4. Caps
for HT1 and HT2 are fine. And HT-side open circuit reverb transformer that
takes its supply from HT2. Can anyone speculate what the order of
destruction was , considering all failures were connected. The broken
resistor was due to tightly regimented construction and use of  turret tag
strip board rather than planar sheet. Strip form can twist with
temp/humidity or vibration and as the resistor leads were straight and tight
, then no give at all.
Owners reporting of final session
"reverb worked for the brief time it was making noise.
before i turned  off  the amp off the last time, it sounded distorted like
it was turned up loud although the i think the channel volume was up with
the master set low so that might explain this.
From what  i remember the volume started to drop fairly slowly and the was a
bit of crackling.I looked round the back and noticed that one of the valves
had melted a bit.  Thats when i figured i should turn it off  to prevent any
damage or further damage."
Am in process of rewinding the transformer after counting off turns of the
original and have restuffed the cap. No overherating of the transformer or
hotspots or shorted turns , mechanical break due to bad winding procedure
allowing the windings to migrate and press over the lead out wire which
broke 5mm from the end.
useful stuff here
http://www.roostamps.co.uk/roostschematics.html
Owner switched off amp when he saw one of the bottles melting , leaving a
deep dimple over the anode but not punctured. Its matching polarity one had
starting to do the same. (Reminder to myself , leave some slack in axial
leaded components, regimented stuff looks fine but this is the practical
downside).  100K bias supply resistor lead had snapped because tightly
joined to 10K phenolic preset wiper, itself mounted on turret tag strip, not
sheet, so plenty of scope to bend with humidity/temp/vib.
At the moment trying to find from the owner what the sequence of distortions
were before final meltdown. As one of the double pack HT electrolytic cans
(for the preamp) is kaput and the reverb transformer seems also kaput.
I would expect .5 to 1R // 1k to 2K but this measured DC and AC R and L , is
0.2R // open, I can never be that sure with high L. Reverb tank disconnected
measures 0.8R and 165R. I'm fine with restuffing can electros ,Main HT
seriesed electros seem ok, and cannot see how loss of bias would blow preamp
stuff. Unwinding/Rewinding small reverb tr will be something different.
The output matching transformer is 27R/27R ie the same , does that mean
bifilar? seems unusual
That was quite painless. I suppose as audio, between mains frequency and
SMPS f., T&I iron lamination but air gap, all E in one varnished lump and
all I in one lump. Between interlaced I&E iron of mains and ferrite
airgapped of smps. 34.48gm of  bobbin,terminals, thick wire and the broken
0.13mm wire . On outside winding , should count off easily via paint
stripper softening or hot air  and weight if not. No obvious overheating on
the outside or telltale melting of the bobbin at the now revealed centre.
I suspect just marginal overheating combined with too much wire , it is
seriously squashed up on the bobbin to have got it slid over the E plates,
and pehaps just a mechanical break somewhere, but it did occur in the same
session as the loss of bias meltdown.
Counted off with no breaks, paint stripper on outer layer and then blast of
hot air if the wire was "grabbing" . No hot spot or shorted turns. Break 5mm
from the end due to mechanical strain presumably.
No wonder only 0.2R over the inner coil , it is .78mm diameter wire.  3 amps
of audio ac expected ? , I can see 0.6mm wire going back there ,or whatever,
for 1 layer of same number of turns
 1 and a part layers , the part layer had ruckled under the tape allowing
the thin wire turns to drop off  at the ends , hence grabbing on counting
off, and pushing radially over  the wire lead-out, especially as a few part
turns to take up the recess from the thick wire part turn. Surprisingly no
obvious punch through between primary and secondary (which is which in this
circumstance?) as ruckling had allowed fine wires to touch thick wires it
would seem, bypassing the intended interlayer tape
speakers 15R//15R , measured 6.6R
Rola Celestion G12/5-
2x32uF in can, terminals blown off, restuffed the can with 2x50uF ,450V , ovalling 
the can a bit to make space.
HT fuse , 1R to gnd
4x 1K, 10W vit to p4
Tr 5.5R// gy-be 13.6R, W-gnd 38.5R, heaters <0.1R
3pin din to reverb tank .8R , 165R
For rewound reverb tr .4R and 285R
feeding 400Hz with low power ordinary 600R sig gen to fine wire side
2.63V .275mA in // 17.8mA,0.042V out
mains tr 4.9R
op tr 2x 26.0R , matching , bifilar ? marked 1A1 496
At 50 percent mains 
158V ac gy-be
main Caps 223,111,207,197,217,109,218


Ross model 10 practise amp
uses TDA2030, 0.1R

Samson Expedition EX30, 2001
Racing tape transport reported but not 
happening when I tried it.
Obviously been knocked as the mono/stereo 
switch was very bad, needed replacement as 
had been puushed in. The speed pot looked skew 
as well as loss of detent so likely problem as disconnecting 
the lines to that causes the motor to race.
Took apart and reassembled but no problem found 
Both 12V feeds need to go to 
the speed board to fully function
Measurements at 50K pot (mid detent )/presets 
disconnected from motor section
'0'preset 850, -12 1230R, +12 16.4K
10R next the 7809
With blue LED driven off sig gen in dark  room 
the motor flywheel speeds were 21.3Hz, 24.1, and 
27.2Hz at ends and detent.
on tape 7812A, 200R,1/2W 150R, TA8142
The 2 orange fibre washers are necessary to avoid an 
earth loop with the metal front tape unit panel. 
without them then a bassy rumble on the audio.
Problem was mechanical at the pimch wheel, lack 
of closure force due to bent/misaligned 
levers under fouling . Could not 
find the real fault in there and a loose 
torsion spring in the housing was probably associated.
Bent the metalwork a bit but that left the eject 
function a bit iffy , requiring play button 
to be pulled out before eject would function
12 in 8R,250W and 8R 50W horn.
Bottom section removal is possible to save the weight 
of 4 off 12V batteries.
Access to the pa is not via the side heatsink. 
You have to remove the speaker section , 
unplug the pa leads from inside , including 
the earth straps before you can remove
the pa via the side.
Most leads have DC function labelling on overlay
pa uses 3x2068, TA7313, 2x TDA7294, n/c thermal sw

Schaller acoustic guitar "pick-up"
Lead unsoldered/broken-away insde the pickup
Thick brass body so difficult to solder 
coax to it and not melt the insulation.
Drill small hole throught the brass and 
countersink for the head. Bolt inside 
a small solder tag.

Another acoustic guitar transducer
same sort of problem, wire can rotate 
and eventually breaks up at the pickup inlet.
No known make "Made in W Germany" 
and a delta shape logo. Cut away the lead to 
poke a rod in the hole to prize off the cover 
disc. Filed the slot larger to tightly 
take the wire and a nylon cable tie. 
Loop the tie tight around the wire on the 
outside and feed wire and tie tail inside. 
Pull tight and place another cable tie grip 
only on the inside to anchor.

Session Duette Guitar,(name of amp) from 1986
As well as dealing with immediate problem and other issues, like perished rubber drive bands to hold (just ) the tank in place and sometime thereafter free to fall amongst all and sundry.
The BDV64B and 65B are presumably held with epoxy to their vaned heatsinks, nothing mechanical. 30 years integrity of epoxy? I assume I'm duty now bound to add fixings, after trying to prize apart one with fingernail insertion, still holding. Was this a common practice then and reliable since, or would it be zinc oxide white goo bonding, to some extent, over 30 years and original reliance was just on the transistor leads not bending with vibration etc ?
The vanes are screw fixed to the pcb but not transistors to heatsinks 
no fixing holes in the vane at the TOP3 sites and no signs of scratching of the black coating to the heatsinks to indicate the one-time presence of and springs, which would have to be long clumsey things.
A couple of silicone rubber bands will go in there , as belt and braces, as well as a couple for holding the tank in place.
So far the circuit looks like W-S site, RG30/SG30 schematics 
ch  change footsw operates in dual mode only
Bypass contacts kill amp on phones,return and ext sp, RET leaves amp noise.
Broken fuseholder .
Main problem burnt wire that was free to touch 1R5 resistor and burnt pcb under both 1R5, had led to fuse blowing previously.
remove lower 5 sc ,only,to remove wooden back panel with the amp 
Make sure the wires are tied back when finished. Removed both 1R5 and 
extended the short end with wire to remount further off the board and a 
couple of PTFE "thru-chassis feeds" as standoffs.
A ptfe block and silicone band around each TOP3 plus some RTV to 
keep in place , as well as the 1R5 standoffs
2x 470R at zeners, 4x 072, 2x MPSA92, BD139
tank 717R and 33R
bad solder on a 1/4 inch so. was causing cutting out
desolder marked sp wires and marked tank wires, refit with a couple of 
silone rubber bands in place of the originals
3 ms , 2 wood sc and a couple of staples removed to access the rear of the pcb but keep wired up.
ext sp in series
phones level seems low
sp Celestion G10C-30
high o/p  will cut out, no hiss 
momentary sw off mains and on again will restart
+/- 33V on heatsinks after cutting out
good ac on speaker terminal.
sw off mains and sp imp >9K
part cutting cone and lifting spider, no discolouration of VC, 
break at the bend VC former to cone

Sessionette 75 1986 (Ward)
3x 3.15A internal  fuses
TL071, 3x TL072, 470R 1W
2N3053,2x 680R 3W, 2SK226, 2SJ82
4R7 3W, 220 1W phones dropper
sp 5.9R, or wire grounded to basket, beware testing with loose pcb
Tank 24,720R
Bad fuse holder replaced
2x680R needed support, 2 strips of paxolin with hole either end to take 
the 2 Rs angled apart, so strip will stay in place.
Main pcb flapping about, failed standoffs
clean and reseat opamps
undo top pots +I/P and some ties enough space to check 2x 1N4745A
pots 10KA,220KB,10KA,220KA,10KB,10KA,10KB,470KB
PA Qs, 2x A872,2x C2547, MPSA92 at diode , 47R 100R
ch sw wires Bn Bk W & W,Be,Y
tighten powerFET bolts

Shure 518SA Unisphere B. The dome was mangled from being dropped a few times
but electronically fine.
Bashing the proud parts of the dome with a lead-faced hammer , dome cupped
in hand , has improved that immensely . And oven cleaner has removed all the
tobacco and gunge, perhaps too well. But there is an overall cant to the
dome, there before I got to it, how to bring it back to axial?
The ring around the outside of the dome is still in place
The thread is 34.6 mm / 1  3/8 inch ? external diameter , what metalic
something to screw in there rather than the mic body , or avoid
lathe-turning a thread on a bar? or how to grip the interior ledge of the
mount , inside the dome, with an expanding chuck or something ,lay the dome
in a padded hollow of some sort, and lean into it with the bar to grip or
whatever.
Did not require as much force as I thought and vaguely screwing the mesh
dome over a length of 35mm diameter plastic waste-water pipe was all that
was needed, pushing dome into a block of expanded polystyrene
Dart point in socket pins to close up 
Small O ring over XLR seriously stretched to pad out gap
95mm circle of reticulated foam (pan scourer) anti spittle layer
replaced foam inside the dome

Simms Watts AP50 , c1976 stage amp
No bass due to broken pot.
Supplies are 40,-40V and 17V
8V on the wire bridge of the pre-amp

Replacing a thermionic valve rectifier with silicon diodes,
ie "solid state rectifier" for 5u4, 5ar4 or 5y3 replacement
Measuring an epoxied-in commercial one , 
via a bench power supply, 
so low volts, for Fender
Combo amps and those 3 tube/valve types would suggest
pin 2 not connected
pin4 to pin8 , 2 seriesed 1N4007 (say) (cathode to 8 end), 0 ohms added
pin6 to pin8 , 2 seriesed 1N4007 (say) (cathode to 8 end), 0 ohms added
So no resistors added for "sag" it would seem
I assume there would not be a low ohm positive temp coefficient thermistor
in each diode line but could there be a voltage dependent resistor or 2 as I
only powered from a normal bench power supply.
I would add 50R or 100R, 10W as a sag resistor between the commoned cathodes and pin 8 
and 4 diodes in all. 
2 1n4007 and 100R measured 70 percent "goodness" on Avo CT160 tester at 120mA current setting, 
75 percent is usual reading for a thermionic double rectifier.

Sound City , for schema etc also see Hiwatt

Sound city 30R, 1987, GDR German Democratic Republic
Squeels and bangs and intermittent failure
Strange mustard yellow and more usual green copper carbonate 
corrossion in the area around both fuses. 
Replaced both by grinding out rivets, drilling a central 
hole and bolting in 20mm fuse holders.
Main caps 18 and 38V wrt ground.
3 loose cropped component wires loose on the main pcb trackside,
Uses 2x KD606 (70W, 60V, 10A NPN ), SD339 TO126, SF118B, SF828D, 
aand TO92 type ones marked
EW4 C37
EW3 C39
EW3 C38 etc
EW* is the date code and for C3 replace with SC33 and SC337== BC237, 
"C" is low power, low frequency, "S" is switching, "D" is
high power, low frequency and "F" is low power, high frequency.  
For reading these and specs/equivalents and other GDR components
http://www.elektron-bbs.de/elektronik/tabellen/ddr/transis.htm
http://www.elektron-bbs.de/elektronik/tabellen/datum.htm
http://www.tu-chemnitz.de/etit/zentral/ddr/index.php
http://www.dl7avf.info/charts/semi/siltmax.html
Reverb pcb has 30.8 and 20.8V on the extreme wires
reverb details tank taken but mislayed, maybe 300R and 40R
2 second hash noise at switch on is the same at switch off so probably 
normal power rail imbalnce issue, no relay, not failing cap.

Sound City 50 plus valve amp
One EL34 glowing excessively
Bad solder connection to the bias pot of this valve.

Sound Lab GTX 100 guitar tuner
Not a fault as such but a modification.
The Candleclub,Southampton
Is an amateur performance venue with mainly singer guitarists making their first 
appearance on stage where the noise,lights and maybe insufficient foldback make it very 
difficult for the unexperienced to tune their guitar up on stage.
A borrowed guitat tuner and one i donated to them both had the 
flaw that if left in line with the pickup lead whether the tuner 
was on or off meant reduced signal level to the amp. This is due 
to the monitoring circuitry loading the signal line.
There was just room to mount a standard 2 pole toggle switch 
in the box if the solder tags to the switch were cut down. Then 
one pole in line with the battery and the other pole cutting 
in the input. This required a cut in the trace between the feed 
through 1/4 inch jack sockets input and output where it 
branches off to the rest of the circuitry. Mounted (ruggedised) in a steel 
box with no top and one side missing to take the signal leads 
it could be left permanently in line with the pick up lead and be trodden 
on without coming to grief. 

Sound System Music Ltd , AC Euro, AC 360, mixer amp, 1996
No audio output.
Inferred history as bought at auction.
Someone had tried tracing source of crack noises,  
replaced one TL074 , not the one causing noise, with the wrong type of op-amp and 
also bent the pins forcing the replaced DC lead to the mixer the wrong way round.
Poor soldering on all ICs , not domed up around the IC pins, 
so one o/p pin solder joint bad.
First thing is polarise mark the indirect power connector, 
diode protected nevertheless .
Sequence is phono; from springline, to springline,audio o/p ; 
plus , gnd, -
No load DC rails were +-66V on 63V caps
Dropping 50 V over each 470R to give +-16V 
(15V zeners). Put some insulation on the interboard 
buses at output end as they were bent and could easily have touched.
Amp used 10P16 and 10N16, MPSA42 and 92 and 1R,3W
Silk screen pcb printing showed 5 amp fuses uprated to 6.3A and 
2SJ162 changed to 10P16 and 2SK1058 changed to 10N16.
On another occassion , bangs and pops on the output 
when touching the casing or lead yanking.
Solder joints failed on the thru-board pins on the PA that 
take the speaker lead wires.

Soundcraft Compact 4, small mixer , 2005
More a case of lack of use, certainly not due to wear , and as I can see the grease oozing out of the spindle area, presumably compacted grease spots on the tracks.
2 main rotary stereo pots are bad I don't mind attending to individually
but half the other such 30 or so  rotary pots are "scratchy".
I think I'll use my modified electric toothbrush head and methylated spirits squirted in the convenient access hole in these Alpha pots, agitating via the toothbrush reciprocating motion , while plenty of meths inside, in the first instance.
Any other ideas? desoldering a load of stereo rotary pots with plated through holes and very close SMD active devices is asking for colateral damage. How to get the grease out or at least redistributed without removing the pots.
BTW intrusion of graphic designer cobblers?, its impossible for an owner to remove the DC power connector without pliers or by pulling the lead at the wrong angle, ie straining the usual failure position, because recessed into the side cheeks. 
I do wonder how long the pot makers have known about the problem with the lubricant migrating and the very flimsy wiper metal used in the SMD era sub16mm pots era. The grase has to only bind a bit and solidify a bit and the wipers will lift off the track. Ive never seen a worn track on one of these pots. 
toothbrush wheeze on the pots has made this usable again, for how long? the amount of grease around the spindle must be limited at the outset 
knobs R, 3x Gy,Y,W/Gy

Souncraft Spirit SX , 2001
Distorted sound , all mounting screws for the pcb were loose , need 
laquering in. 17-0-17 supply , break in the central line. 
To remove 1/4 inch socket bush nuts 1/6 turn only as turnbuckles , not nuts.
Lage self taps along front edges, mixture of machine and self tap so note. 
Leave screws in sides to remove the metal top and sides.
Some date (the slide switch) DVM diode test unpowered
,,,.84,.84,1.3,1.1,1.1,1.2, .87,.87,1.2,.8,.8,1.2,
.8,.8,1.3,,88,.88,1.3,.88,.88,1.2,.88,.88,1.3.
sw position not noted
Fluke 77, .18V ac 400Hz in ch1 , 1/2 way all pots , sliders 
on "0" db. Top 7 traces along top near ps
.08,.13,.15,.15,.14,0,0 V ac
For ch 1 and just top pins of each pot 
.25,.28,.67,.36,.68,.28,.68, .38V ac (this one 5 pins down from top pin) 
using ground point at bottom of the board.

Soundlab PMX 802D, 1984?
R channel went down after about an hour of use, 
recovering later.
Tended to the usual suspects. Protection 
relay and IC controlls both channels 
so not the problem unless relay problem.
8 pin SIL Marked C1237HA , on overlay PC1237 
and found datasheet on net under NEC uPC1237HA.
The leads from R and L channel (to one of the 
o/p device emitters) to 
the protection circuit annoyingly marked red and 
black , if disconnected will not 
disable th erelay click over
Most annoying there is not a standard 
overlay for the power device orientations 
on the overlay. Replaced one , with very 
bad green corrosion , the wrong way round 
and blew the amp. 
I determined the schematic for this amp.
Unusually all devices are marked on the overlay 
as their type number, not circuit numbers.
They all face the same way ecept 
the D600 next to the TIP42c, excluding the 4 
output devices.
Replaced 2sc2344 (tip41c on overlay) with 2SC4159 
and 2SA1011 (tip42C) with 2SA968
rails
Digital 5V and 8,0,0
main ps +/-48V
mixer ps -14,14,0,0,14
main board of mixer +/-10.5 V on op amps
-14,14,0,0,0,0,0, on ribbon
end board of mixer , on ribbon
0,0,0,-14,0,14,0,7x 0
240V primary 3.8R, <>0.15R per secondary
ps disconnected pa , "diode " test +/- to 
gnd 1.9 to 2.0V one way and >2.1V the other, alternate each way.
Load test of one channel with thermometer 
mounted over the heatsink.
400 Hz giving 8V in 4 ohm load.
30 minutes to stabilize at 33 deg C over ambient, dropping 
0.5V ac in that time.
This amp returned a few years later with a new owner , my foregooing holding up.
This time beer spilt over the top. Could not use the reverb and then dead.
Bar graph flashes up at sw on then dead. 
Bad mains sw. Cut open the recess to take a larger standard size sw and replaced solder 
with spade terminals to make any return visit easier to separate the halves.
Delay board 74LS624, 311D, M50195P mitsu, HM4864P-2
Effects send pot problem solder at one end giving "spacey" sound especially in 0 posistion.
3 large screws under the front ledge.
L and R 1.3UH output coils touching but ok. 
400 Hz, 1mV , ch 2 , all mid, sw out, slider at 0 
2x7 ribbon , lines from red
13.9, 0,0,0,0,.01,.01
0, -13.8, 0, -13.1
AC 0,0,1mV, 0,0,6mV,6mV

Soundlab SP 800 amp, 2002
Anyone familiar with this amp? worked for years with the present owner but
there is a quantity of circuit , each channel , that has been removed. A
"friend" decided to short a speaker line to give the current fault , but I'm
faced with a lot of post-production modification that does not look made by
the manufacturer.
Cropped tr legs and desoldered Rs,Cs, 4Tr,7R,2C all x2. Removed at
manufacture or previous owner?
Leaving this circuit in place with 2 Triac/scr. Unknown TO92 size SCR (on
overlay) marked (unclear on each channel examples)
08D
09
2 lines from the disconnected circuitry went to the left and rightmost pins
of that SCR. Nothing at any time to the centre pin. C is actually 2 back to
back 220uF, 50V for pseudo unpolarised C.
May need to change font for equal space font for the following


o-------------------------------|---o Speaker
         |                     .-.
         |                     | |
         |                     | | 10K
         |BTB24-600            '-'
         '                      |
        _|_/o-------------o  o  o
        V_A             SCR     |
         |                      |
         |                      |
         |                      |
         |                      |
         |                     ---
         |                     ---  110uF,100V
         |                      |
  o------'-------------------------------o Ground


Can anyone identify the SCR ?
I cannot identify as small SCR or diac in a 3 pin package, represented
as 3 dots, marked SCR  in the ASCII
looks as though someone else has been here with a different amp
http://forum.allaboutcircuits.com/showthread.php?t=23271
... The schematic calls this burnt component a "triac driver sbs bv thresh"
and on its twin (in the non shorted channel) its only labeled "08d 25". This
is in the protection circuit of the amplifier which unloads the outputs if
there is a problem.
...
This is a 3 leaded device btw
so the 09 in my case and 25 for him is probably datecode
googling about ,perhaps a DIAC08D, would that be an 8V diac ? sounds about
right value of bilateral switch for a 400 W amp into 4R
From that previous thread and mention of
MBS4993
I downloaded that datasheet and it looks as though a sort of Darlington
triac arrangement in the soundlab amp
The amp channel failed to s/c , knocking out fuse, so speaker protector did
not come into play.
The way to confirm the identity of this "08D" device is to
remove one and check for a switch action , at about 8V, on a current linited
bench ps.
Another oddity with this amp. Each channel has one floating, nominal zero
DC, connected to true ground by a 50 ohm NTC thermistor, why thermistor ?.
The missing circuitry may relate to fan proportional control of 1 or 2 fans
going by overlays.
Only one , on constantly, in this version. But why the 2 DC lines back from
the output on each channel. This is an all N-channel mosfet amp. Can they
have a DC offset if driven hard?
Inrush thermistor 3.3R
4x 0.1R, 2x 4.7 (at rear) 8x 1.8k 2w, 4x 4k7 2w, 2x 3.9k
Replaced one failed IRFP240 with an IRFP450
12x IRFP240, 4x C4793
One zobell R 4.7R, 2W colours had changed on over 
heating from yellow to brown, green to black, gold to silver
mains tr 4.7R, y-y 0,5R each ch
no load DC readings 
-74,-72.2,-74.5 / (-72.2,0,-76.2 ) x3
-74.2,3.8,-74.6 / (3.8, 76.4, 0.1 ) x3

Sovtek MIG 50, 1993
Rusian guitar amp using 2 off 5881 and 3 off 12AX7
Blowing the 1 amp "valve" fuse.
Each 5881 connected from anode plate to ground via 
390pF,2KV disc ceramic. One of these tiny caps that you 
commonly see in SM PSs had gone s/c between 
the leads. Cracking it open solder ? on the wired faces had 
melted /migrated across. Replaced with physically much 
larger 360pF ,HT caps on each 5881.
Wired the 110/240V switch paddle back to the transformer 
mounting so it could not be accidently flipped to 110V.
V dc with 5881s unplugged and 3 12AX7 present
 both 5881 sockets *.600,600,-61,*,0,0
nearest 12AX7 356,33,51,0,0,326,35,51,0
182,0,1.2,32,32,304,0,183,32
178,0,1.2,32,32,216,0,1.7,32
o/p matcher Transformer dc ohms 53 each winding 
and 1KHz ac L of 3.2H each winding and 19.4H end to end

Speakon loudspeaker connectors
(and pirated copies) 
, I noticed the R symbol on a Neutrik line plug
(4 way) that was mated with a no R, Cliff (2 way or maybe only 2 of 4 way)
chassis socket, they meshed and locked together and functioned fine as far as
i could feel/ see.
Apparently the 'blue' series are rated at 20 amps at max 120 volts.
Neutrik NL4`s are rated 30 amps for the 'old type' and 40 amps for the 
newer X series.

Spear MV07060208 with 2 EMGHZ pick ups 
All controls loose 
47uF cap wire uninsulated touching pot body
EMGHZ
bridge and fingerboard ones different
7.4K , 7.9H 
7.2K, 4.0H
7 to 8mm gap between open strings and polepieces on fingerboard
4 to 6 mm for bridge

Spirit Powerstation 350 (Soundcraft) 350W Mixer / Amp.
Mixer OK but no power outputs.
The mute lamp (speakers disengaged) permanently lit.
Nothing wrong with the pa it was failure of the protection circuitry itself.
1/4 of the LM2901 (driver to relays) had o/p held to negative rail.

Spirit Powerstation 350
No power o/p,monitor o/p ok
Failure preceded by clipping LED illuminated falsely ie no clipping.
Probably one TDA7294 failing putting DC on o/p then second TDA 
blew and muting circuit cut in. On powering up excessive heat on 
main heatsink but all fuses OK. Trying to isolate which of the 4 
power ICs failed removed pairs of fuses and a 100uF,63V cap 
blew up. Without + and - 42V to the o/ps there is -15V on the IC 
and reverse polarises some of the caps. This associated 
(third) power IC was ok just a blown cap. Both failed ICs were 
resistive to -42V rail. Good ICs ,out of circuit, about .5 +supply 
pin to o/p pin on DVM diode check and about .5V -supply pin 
to op pin. As resistive rather than short took a lot of 
current but not enough to blow any of the fuses.

Squier Bronco Bass guitar
Missing .25 in so bush nut, replaced inner nut with  washer and then nut and washer outside
Broken fisrt pot, 500K, pickup 5K

Squier sidekick guitar amp.
Broken away pcb from the front pannel
Weak 1/4 inch i/p socket had the back-nut come off the bush which meant 
user straining the pcb when plugging in the guitar lead leading to breaking of
 all pots.Replace with i/p socket mounted on the chassis and wired to 
the pcb and replaced all pots.

Squire Roadrunner Junior double disco deck and amp
OK driving one 8 ohm speaker but distortion driving 2 giving 4 ohm (designed limit)
The power output monoblock presumably has 4 o/p devices 2 in parallel 
for +excursion and 2 for -excursion.One tranny had presumably gone 
o/c so expensive monoblock replacement.

Sqire fog machine,no model number but 1993 and 
using MC1458N and LM324N on main board.
No smoke output.
No snubber network across the solenoid glycol pump so added one 
and changed the blown triac with a higher rated triac.

S R Technology Club 60/A
Dropped onto wooden floor then distorted output
pots at 1/2, .1V 400 Hxz in , .1V mixed line op, low level at sp with background buzz. 
In cct with xover 6.3R (B) .6R (T)
7.1R r-bk amp op terminals
3R8 both Tx sec.
2x680R, 4R7
5x072, CA3080E, LM3386T
Above 1V in and op sort of clipping distortion
+/-34V on the LM , mute -3V
ip p9 & p10 rounded sawtooth waveform going to spikes with more signal, same as op 
so preamp problem somewhere
With no tesyt input but applying 400Hz to , in turn, p9 and p10 then 
good sine op (with some mains hum )
+/-15.2V for th eopamp supplies
Labelling ICs from the CA around the U shape then IC4 at the pots header was ok 
on p1 and p7
IC5 p7 was soft cornered square wave
No electrol shorts
IC4p7 via 470R to line out
IC5 p2 and p3 close to neg rail V
Replaced the 072
.1V 500Hz in , mid pots, 1.84V over its speaker

Stage Line TXS - 150 SET, 1998
Dropped and then no funstion
"re-coning" dynamic microphones?
Not this time as I used the core of a Shure dynamic mic as a parts mule for
a dropped radio mic, but just wondering if it can be done for some worthy of
repairing expensive mic in the future.
Both the Shure and the one with the broken hair-fine wire of the voice-coil
have a thin diaphragm glued to a rigid surround . For speaker re-coning the
cone is quite substantial and heat tolerant compared to this diaphragm
material and hot-air heating usually removed the supension surface from the
basket, but I doubt that process is possible with a mic - anyone been here
before?
As part of the fitting I intend using silicon rubber rather  than the more
rigid rubber of the originals, any thoughts as to any effect on sound
quality? I was thinking a less rigid support may give more allowance as far
as not transmitting shock-loads to the mic core . Initially I was wondering
about a material more like a spring would give a reverb-tank spring-lime/joy
spring reverberant character but then remembered a lot of studio mics are
surrounded by springs.
Well I seemed to have learnt something by burrowing in. Has anyone come
across failure of a microphone from having been laid down against the
heatsink of an amplifier ?
I desoldered the VC tails and then with a warmed blunted needle lifted the
diaphragm from the rim, without any obvious deformation. It looks as though
the VC is held to the diaphragm with a wax of some sort, ie relatively low
temperature melting.
So microphone assembly construction, I assume is something like this
melt a thin line of wax over the end of the former , the thickness of the
former
lay the VC in the hole in the magnet
solder the 2 tails
lay a thin layer of wax in the preformed hollow of the diaphragm , of
diameter a bit larger to a bit smaller than the VC former diameter
with a carefully controlled amount of DC or some sophisticated signal to the
coil , to make the VC move towards the diaphragm evenly and centrally locate
itself with even air gap to the magnet gap (perhaps an active system
monitoring capacitance between VC and magnet body)
a blast of warm air , perhaps only about 80 deg C to melt the wax , in the
central area of the diaphragm
keep the centralising signal present while the wax cools
I won't bother unwinding 1 turn off the VC and reassembling as it was only a
basic mic to start with and I've a robbed a mic core to replace it with
anyway, with just adjustment of the suspension rubber as a different size
rather than that wax business
I suspect instead of wax the joining was via UV cured epoxy on further exploring of the diaphragm
Electronics VXM286TS under the battery
RS Q? ADP 28
Philips SA571D,4558,14.603 xtal (red ch)
01.17.94 on overlay
2 sc escutcheon and ring falls away
soldering iron break the wax and pull out the mic guts, under x30 can see the wire break 
at the VC
For Shure mic 561F , 1 minute of conical soldering iron tip on the small allen key grub 
screw mad eno difference to loosening. Dremmel + .5mm disc cut in to make a slot but still no 
shifting. Continued grinding through the grub and swinging , in an undercut sense, 
to remove all the grub and the 2 Al parts come apart with twisting, no screw threads.
Back to wirelss mic, the battery terminals needed tightening and lacquering.
Insert rf pcb through then sw cover , then slot in the escutcheon, held in place 
with the ring

Stagg foot pedal
wrong cable entry gland so cable can turn , fix with hotmelt glue inside. 
Bronze tip 1/4 inch jack may have internal short, replaced

Stairville lamp, model number absent ,perhaps PAR 56, 13 LEDs on a diameter, 2009
Some red LEDs out and then all blue LEDs stopped
Tx 167R/1.4R
28pin pic/uC, 4093,7805, SN76176BP
On the LED board all SMRs measured ok
+RGB header
+12V to the ring trace and 0V to blue common about 1/3 of the blue lit feebly
then 1/2 Gn + some feint
then 1/R plus some feint
70R measured i nthe Gn supply line 
2R over R and o/c over blue.
Failed fuse i nthe blue line and corrossion on the brass button for the fuse on the G fuse
PbF failure of  20mm fuse ?
How to determine whether tinpest layer round an end of the filament or a physical break?, just durious as to 
failure mode. 200mm F type. Breaking the glass is likely to disrupt the failure situation. Filament seems to be in 
proper place , diagonal along the visible part of the tube and no observable movement on normal handling. 
No circuit failure to have caused long term aging stress failure of the filament at one end. I've not tried 
500V/1000V insulation test (could perhaps marginally "weld" the failure) but DVM-R >30M 
Tried the fuse on 500V insulation tester with 10M in line and >500M ohm measured 
Set fuse in an open frame fuse holder. Ground into the glass until it cracked. Could insert a needle in there 
and o/c in both directions.
One end broken , whether by me , unknown, other end fixed in. Crush the glass in preset mole-grips and then 
I decided to prize out the caps from the holder with a blade and the one with the still captive filament went 
flying across the room .
One of the 7 red LEDs in a row was defunct, applying a bit less than 12V 
to that LED side of its SMR, replaced and that row came up again


Stairville DMX Master 1 lighting controller , 2006, marked PbF and RoHS
And indeed failure of heatsinky solder on crude o/p XLR socket.
Redid all external fittings and 7805, XLR have only 1 of 4 fixings used
Then later
If someone changed the polarity by changing the switch at the rear of a
lighing controller what would be the result?
Assuming fully working order beforehand.
1 no lamps controlled
2 erroneous lamps controlled and erroneous control
3 correct lamps but erroneous control
would a symptom of erroneous control be say by sliding up the blue content
then G and or R component of lighting drops
Something like situation 3 - maybe a bit garbled, in
phone call about "broken" controller , but someone had flipped the switch on
the back

Studiomaster Powerhouse 8-2 500W mixer amp
For renovation of sliders but a few points in passing.
The fan duct over the power devices was half clogged with 
fluff. R53 and R68 10ohm,1W resistors were charred and 
replaced with 3x3.3W in series. There are a number of 
non-localised and non polarised interboard connectors on 
this m/c so mark before removing and make sure on reassembly 
not be 1 pin out ie 0to1 ,1to2 ,2to 3 etc.

Studiomaster Powerthouse 300 8.2, 1996
Dismatling pa, remove plastic snap rivets from underneath and remove black bits from pillars 
when pssible , reintroduce on reassembly. Fit only the 2 rearmost pillars to th ebase plate 
on refitting , for alignment. 
I'm being spun the story that this was put into storage and on powering up
again , just the mixer section was working.
So the following is hypothetical but is it a possible scenario?
Does not say anywhere that this amp can be bridged, but also does not say it
can't be bridged so perhaps a green light to the owner to run both channels
together.
Anyway blown fuses and some shorted TO3 in both channels. One 16 amp rated
relay had an obvious brown patch inside its casing, opposite the contacts,
but still worked at test levels when the active was replaced. The good
looking one did not click over but its coil ok and audio output up to the
one contact . Both replaced as due to overheating, the plastic linkage from
contact carrier back to flip lever are melted/deformed. The brown stained
one has a serious pitting , well reverse of a pit, sticking out of a
contact.
Now if due to dirt or initial pitting , then poor contact and then making
and breaking current under serious load could that in combination with
speaker insductance create spikes of a few hundred volts to knock out active
in both channels ?
If the bad relay was passing less amps than it should, then excess load on
the other relay and so both overheat.
If DC passed to the speakers , from blown TO3, due to a short in speaker
lead say, then I doubt the situation would last long enough to cause the
relays to overheat from assumed  good state previously
Occams's raison again , more likely scenario 
User did something stupid to one side and blew it up, then they did 
the same to the other side.
LEDs work, phones op , no pa output.
No relay click over.
low amp fuses ok
fuse next to main caps ok , 3 other blown
37V dc over F2 and F4 hours after trying power so discharge the caps.
Check what standoffs have rivets under and unclip those ones only on the pcb. 
One of the screws holding central screen plate to the main h/s is laying 
in the bottom of the chassis so could have shorted something under the pa
Undo conn1 , fan spades, R to daughter boards and 1/4 in sp o/p 
pa SM2814B
2SD1763
BDX330
4x MJ15004, 4x MJ15003
( 2 x 2N3773 instead of the original 15003)
ea amp centre 10R
10R 4 x .22R
4x .1R 2x R56 and .1R W/W
Remove all TO3 bolts to find shorted TO3
TO220 al test ok "diode" test
3 shorted , replaced with MJ15024 and MJ15025
From main caps fuses are 2x5A(T), 2 xT2 then 2 x T1
Testing without mixer and main pcb upside down. 
2 larger 30 amp rated relays are now wired in there, I will leave at that as
far as mods are concerned. Exploring the originals it looks as though even
when new and good there is only just sufficient closing force and movement
to close the contacts. Then with perhaps "normal" heating of 16 amps passing
through, then the plastic mount for the contact carriers may deform slightly
under the on-action and enlarge the gaps. So progressively worse.
Make soure the mumetal arount Tx is well covered as touching the LM7915 reg h/s 
will knock out both 1A fuses
60% mains , ignore XLR grounding rings
TO220 Vdc "front" to "back" with 20mV 400 Hz in R Return so, .8V ac over 8R load
-1.1,-30.3,0
-.5,1,-1.1
1,30.3,0
-----------
-1.1,-30.5,0
-.4,1.1,-1
1.1,30.5,0
with 60% 1 and 9.7V across relay coils
R is front amp 
initially no op L amp due to relay fault
Still 60% mains dc and ac on daughter board pinnings with 20mV 400 Hz in and only measuring with 
DVM ac and dc.
First 6/6/6 pin daughter pcb
-12.3,0,0,0,0,11.4 dc / ac 22mV,17,25,13,13,19mV / 0,3.6V dc (39mV ac) , 3.6,4.1, 4.1,0
first of th ecentral boards 6/5
0,0,0,11,4,0,0 dc / 0 (33mv ac) ,11.4,0,0,0 dc 
back 6/5
ac 0,0.9,10.4, .04, -, 0 / .9, 10.4, -, - , 0
dc 0,2.5, 0,-12.2, 1.4 / - , 0, 11.4, -12.3, -1.3
80 % mains , DC at fuses +/_42V
100% " " +/-54V
Someone previously had replaced one of the 1/4 inch speaker sockets, very
pro looking soldering and heatshrink , but on the wrong pins on closer
inspection.
Connected to tip and ring rather than tip and sleeve of a stereo socket,
ground to tip. So worked fine with mono plugs , presumably no one noticed
antiphase sound. Then someone presumably tried it in bridge mode. 
Make sure that if the 1/4 in sp so come loose then the tags or solder cannot touch the 
steel divider sheet.
The fan was very reluctant to come on from idle, much higher temp than 
I would have thought likely.
Release the 2x D1763 from h/s and using hot air gun
TP1 6.61V to 6.1V heating front D1763 down to 6.1V, TP2 6.62V rear down to 6.2V, 
TP3 4.8V, 4 4.83V
Fan having only 14.45 and 9.58V over it
2 BA4560 on relevant daughter board
p9 from Tx end goes to base of TR13 at fan 
TP1 to p10 of daughter
TP2 to p11
TP3 to p14
TP4 to p15
IC6 probed and seemed ok
-13.7,6.6,5.5,-15,5.3,6.6,-13.7,15.2
D1763 rearmost .59V,6.6,0 , same as frontmost, cold
2K to gnd brings down to 4.7V fan on high, TR13(b) .86V
560R , 6.6V drops to 1.6V , fan high and relays cut out.
3.6K 6.6V to 5.5V no fan speedup but hot air 
to both temp sensor TO220 soon drops to 5.3V and fan speeds up
1.5K on TP1 drops to 3.5V and relays cut out
2.1K , 4.1V relays cut
2.7K , 4.8V relays out
So probably TP3 and PR3 are moitor and set relay cut out point
TP4 and PR4 is fan fast temp
Adjusted PR4 clockwise to drop 6.6V to 6.3 or 6.1V forgot to check properly
Bolted both thermal TO220 back to h/s (both are tied to some extent and both need warming)
Beware of trapping 4 wire lead at the S/R portion of main board, and align 
the XLR ground rings if misaligned
Heating whole H/s from inside the amp with hot air, concentrating at 1/4 and 3/4 
points over the TO220 and monitoring with non contact IR thermometer
Fan speeds up with 35 deg C over one Tr and 31 deg C over the other, a great improvemnent. 
.1V , 400Hz in at returns , 4V over 4R L and R ch
m/s s/c for divider plate
large pk for plate to H/S and laqcuer leaving out the one that loosened
12 pk for mixer top

Studiomaster Powerhouse 8-2  mixer amp, 1994
See aside with Trace Elliot GP12SMX
Looks as though someone tripped over input leads to the XLR sockets in those
2 channels and wrenched the sockets, must have wrenched/cracked the 2 boards
as well.
Probably mixer landed with the , now absent, mains switch hitting something
at the same time. 
Opened up chassis hole to take a larger neoned rocker and glass sleeving 
over the thermistor
2x 1R & 317T on phones board
2/2/2/2/ MJ15003 & 15004
TR16 SM2184, TR15 TIP31C , TR14 BDX330 not necessarily original
8x R1 , 4x 5.6, 8x R22
3x 10R , 3x 4560D
marked +/-65V dc
4 way fuse carrier in the IEC socket, 100/120/220/240 read as the rest of 
script not nearest legend, on end, at the socket.
120V setting 3.9R . 240V 7.9R
2 channels not working, looks as though a speaker plugged into one ch , 
then did the same on the next ch before realising their mistake.
+/-13.6V op amp rails ok but pin7 on IC2 of both ch was 12.3V , not about 0.
Replaced each 4560D , beware of replacing 15w IDC into the gap, not over pins and 
avoid being one pin out also.
Adjascent D2 4148 measured DVM diode test of .4V so replaced it

Studiomaster Powerhouse Vision 8, 1996
Left channel clipping, then dropping out totally after a time, first problem
in preamp, imbalanced gain, second unknown pa or prea. At least possible to
swap the pa channels over, to resolve to pa or prea , if
nothing actually found.
Fan startup, comes on at power up for 2 seconds
(presumably normal) switches off and comes on whan heated.
I've never seen that before, a TO220 device trackside under each pa pcb,
thermally touching the heatsink. Only 2 pins used, the B-E junction, with 2
isolated traces to the umbilical ribbon the carries the low voltage rails
and signal i/p. I wonder what is special in the 2SD1763A used for that
purpose.
I've not got the schematic but I've found you can run it stripped down.
Disconnect the 2 PAs and all the ribbon cables except the one between the ps
one, via small rear panel and up to the mixer. To check for any mixer
problems, removing display and memory stuff, monitor output by phones.
You can then plug in one amp at a time , or
swap around , to localise single channel problem to one ch or the other in
pa or mixer section.
ps ribbon to mixer socket on main board under/between ch8 
HF pot and REV slider
There seems to be odd power rails , +/65V main power rails and a pair of
+/79V.
With pa's and mixer removed and Conn3 and conn4 ribbons removed, so just the
main combined ps and thermal board in place, DC voltages on con3
80,0.2(£),15,0,0
-80,16.6($),0,0,0 (*)
2x5 header volts viewed/monitored at pins , starting from main caps
end
* has 0.6V ac, and £ has 0.2Vac on it with 400Hz input and 0db bar
registered on the meter
$, 16.6V via 100R to base of thermal monitor TO220 ,to test point T12 ,
obviously drops down to Vbe , with pa in place
T10 for the other amp TP
The 0.6V ac also on that pin of conn4, clear and balanced , unlike
originally with all connected, very marked signal imbalance. There was a
problem with the "group" slider , but maybe not the cause of original
problem. I will next try with swapped pas in place, then display board if
all seems well.
At 75 percent or less of mains voltage both red LED "fault" lights light,
gives some sort of check of functioning.
I don't know what temperature is required to activate the yellow LEDs and
channel/channels ? shutdown, but presumably greater than 90 deg c.
You can monitor signal in of the PA at R11 , R9 end.
Monitoring output and T12 TP, increasing the heatsink temp with hot air gun
and fan off. No change in output level up to 90 deg C.
With fan connected , fan comes on (at T12) with  Vbe between 0.61 and 0.62
and temp between about 45 and 55 degree C (the "thermal" Tr is underneath),
dropping to 0.52 or so at 90 deg C. Both channels checked like this.
with zero on FB,REV,aux and centre for all else per ch.
 0.1V  input , 400Hz giving clipping point 
max slider, required gain settings between 45 and 55 db for each of the 
8 channels, both sides L & R
purple 116V ac supply
orange 38V ac
check main rail 1/4 spades are recessed before powering up 
disconnected .
To work on the PA and mixer , make extender for the 16w ribbon 
from conn2 of display board and conn under PGM/Edit led .
2 G cramps to fix a piece of gaffer taped dixion vertically 
in the front RH corner and small cramp for top 
of dexion to the mixer panel held vertically above and over back plate.
5 amp mains plug fuse is tool for this torroid.
Added 4 football studs underneath the case, as manky rubbery sheet there.
0.125V, 400Hz i/p at ch1 with full slider , 23dB mid gain, 
mid position of pots, 0dB on master slider , 0dB on bargraph30mV on pan pot 
and 0.56 V ac on R11 of PA resistor
With fan disconnected and 400Hz , 0.1V, 23dB gain, 0dB bargraph , 
3.3V ac over 4 ohm, one channel
thermometer bulb over centre of relevant heatsink cover/locator "pcb", took 40 
minutes to stabilise at 26 deg C over ambient.
The VFD display is very exposed/vulnerable with the mixer pannel 
mounted vertically for testing purposes.
Remove the short ribbon at the rear plate , not under the 
central screening plate. When reassembling I managed 
to trap and pierce a ribbon with a mounting screw, disabelled whole 
of mixwe pannel but no colateral damage other than repairing break on 
line 6 from red on the 14 way lead from front phones board 
to graphic board. Captive nuts not very captive 
so loose end covers/handles. 
Really a 2 person job, one holding a dolly and the 
other hammering a small cold chisel radially into the swaging. 
I tried a large ball-bearing in a cramp but could not 
find a suitable anulus to go round the ball to keep it in place 
while tightening up.

Studiomaster Powerhouse Vision 12, 1996
A previous "repairer" removed all fuses , ratings on  overlay , so ok. But
did not mark the ribbons before removing all of them. Majority are mateable
without ambiguity. There are 2x 16 way ribbons with exactly the same IDC
connectors that could go to either of 2 places on the central board holding
the graphic sliders and LED bargraphs.
Completely different lengths to the ribbons , does not help to decide as the
headers are adjascent
One ribbon is  from Conn1 of rear INSert sockets
The other from the CCD display board
Cannot start rectifying whatever the underlying problem was, before sorting
out this added problem
But a thoughtful designer would make one 18way with 2 redundent or
blocked+cut pin identifier/inhibitor somewhere. As the ps and pa seem to be
ok I don't want to compound the problem. I think a few ground tracing is the
way forward, just requires removing the display board which should be easy
enough
Unfortunately neither 16 way ribbon carries a frame ground. But that board
and the other 2 boards carry plenty of BA4560 and except for a few ohms of
dropper resistors, could match up +/- rail pins 4&8 unambiguously with
definitive, non-matching,  ribbon pinning
So the long one , piggy-backed to the rear inserts board, goes to the header
nearest the graphic sliders.
Short one from the display board to the header nearest the display.
Logical yes, but both are plenty long enough to have been inserted in
either.
Applied half mains and increased to about 80 percent and some magic smoke
appeared from a very lonely looking R112 ,reading a burnt 10 ohm, with a
black band visible , 1/3 W on a rear board with nothing else other than 4
sockets. This connects top frame to base frame grounds, which I had not
cross-connected. 
Red non-polarisor side of 10way
=R57 on 909/911
mixer pannel gnd to main gnd via 10R
C5 on display board
Dug out 2x8 way extender for main to mixer ribbon to work on this amp live.
70 percent mains and outputs +/-1V but go to 75 percent and outputs would
swing up and down to (reduced but large ) rail voltages .s
70% mains and display scrolls through correctly
72% mains and the 4 red LEDs light , green thermal LEDs always off
75% mains LED3 out with a slight flicker and LED4 bright flicker and these violent output swings.
Slight ticking noise , like small reed relay clicking over, coming from something undetermined, 
coils perhaps? 
TR6 was the only thing showing any excess heat on IR thermometer, only about 5 deg C so not relevant 
probably.
80% and serious pulsing manis draw of an amp or so.
Disconnect the mixer pannel and same 
Disconnect both small ribbons from ps to PA and LEds go out
At 75 percent mains +/-48V ac on fuses and 2x43Vac on F1&F2 
and 2x 15V ac on F3 & F4 
Someone must have plugged something they shouldntave in the external inputs.
1x BA4560 there, except for grounded pin3 and 5, all other pins were near
enough at +/-15 voltage.
Fan kicks in , even at 70 percent mains, at power-up initially only when cold.
Disconnected Con5 to rear board with 4x 1/4" so. and the problem goes
Someone must have plugged something they shouldntave in the external inputs.
1x BA4560 there, except for grounded pin3 and 5, all other pins were near
enough at +/-15 voltage
Replaced with TL072
100 percent mains +/-65V main rails
55V ac and 19V ac on other fuses
Eprom board SMD face side is viwable when fixed to the nylon standoffs.
To connect /disconnect internal ribbons - Angle up the top panel with 6 inch 
gap at rear, sliding down and forward an inch so the lower edge of the top panel 
"hinges" between the main slider pot bodies and the top of the front vertical panel of the base. 
The blue display lens will easily push out with handling of the mixer panel .
Meths cleaned off the selotape gunge on the label pads but not some felt pen marker names, 
some paint stripper worked without destroying the white pads.
No Regen function or LED, sw works ok
Mains hash on Left ch on phones and Line-out-L, at start up regardless of standby.
Before the graphic as changing that will change the character of th ehash
Jack into the Insert-L, no change.
Disconnect bus ribbon at phones board then dead, no hiss at high levels on phones.
Reconnect and disconnect all input conns , leave main board conn in place, then hash.
Disconnect bare ribbon from phones panel and hash goes.
Reconnect all the main bus conns, disconnect the simple main to phones ribbon and 
hash goes and good test signal from ch 1 out to phones and Line-outL 
Outer line of this ribbon, away from red side, has a nick out of it, made good and insulated.
Regen line from its sw is p9 (from phones end) of 17 of 34w ribbon, polarisation gap line , 
to display board, to IC8,p8 74HC541. Reseated all ICs on th edisplay board and resoldered 
Rs etc around TR2 seemingly affected by hot-air from previous "repairer"

Sunn alpha four , 1978, mixer amp
Broken pot spindles, the fourth,offset, terminals are not 
bass compensation , just support.
Uses 3x 2n3055, 3x SJ994
2x 140, 4x .33, 2, RC4558, TIP 29
primary DC , 14.5 ohms

Sunn SPL 7000 high power amp
No output either channel and no known history
2 of MJ15023 B-C s/c replaced with MJ15025
Q118 2N5401?
burnt Rs R133=? R160 =100R
C55 .1,100V ?
R109,R110 = 22R ? had gone high
R121 422R
R111 430R
R134,R135 2.2R were o/c
Other Trs C2168,C1567-S,A958,
Q20 A968B
Q22 C2238B
The fan on this amp (UK version) used a 110V 
fan with a dropper so at low temp runs at 50-60V 
then switched out to 110V off the main transformer
In working order each pair of 15023/15022 showed 
.44R E-E and 4.4R B-B
Beware 1/4 inch jack needed in B input for single 
channel use.

Vocalist Live3 digital voice processor/harmonizer,2012
(Vocalist , also see Helicon , related?)
Last time I saw this was non-momentary/non-latching footswitch problem, sorting out the firmware failing by slowing down the switch action. That fudge has worked fine. Now guitar input ok but a noise over the microphone input that is white noise wavering in strength so it sounds just like buffetting gusty wind noise. No change to the hash on jiggling anything external. I've recorded the noise and are uncertain whether the wavering is random or complex cycling in nature. I wonder if there will be a cure this time, barely 2 years old. 
Just before opening it up, I noticed the phantom button, in on position. Repowering again 48V on and switching off, after 5 sec or so the intrusion noise went. Testing for 48V , something tries to establish on the mic line but drops to 0V over about 5 seconds. So the 48V subcircuit needs exploring 
Thought I'd start from the 48V switch trying to locate the generator. But multiplexed into the uP like all the other switches. Only 63V caps are at the mic input and L&R outputs. Other end of the board is a DC/DC type inductive core lump next to 6 pin SMD IF8CG but no info found on that topcode.
The owner was concerned as to whether he'd done something stupid, despite it failing mid-song. Does owner psychology mean he did something stupid, soon before the failure? 
That supply seems to be for 3.3V.
Looked for 2x 6.8K resistors at the XLR in and 2 are present, common of those goes via control Q17 and Q18 and some small droppers to a 5 pin SMD U23 and an even smaller inductor. U23 Marked
052
671
483
no info found of course playing with those numbers. p1 and p5 inductor/supply from 5V regulator, 2 gnd, 3 to diode, 4 output. 
 As it happens , ironically, no fancy expensive DC powered mics used as the input.
The 48V is "blocked" from an NJM2122 low noise op-amp by 63V 33uF electro and 10K . Replaced the 33uF with 47uF63V. 
and smaller 4.7uf replaced with doubled up 2.2uF. 
Managed to break a pin on the gain pot, misaligning on reassembly. 
soldered across and reinforced with hotmelt. 
Grease on all pot shafts so lifted wipers wil lbe the next problem.
But of course switching on the 48V transfers across the cap to the opamp input, rated +/-10V maximum. In the normal run of things is 10K adequate and this failure is just random? Would an op-amp with +/-20V rails or larger permissible input maximum voltages more likely to survive? No obvious (all SMD) clamping zeners seen in the circuit, add some 3.3V  zeners  ?, at the cap or opamp input? , or any other known work-around this proplem? (other than disabling the 48V supply which would be the easy option, after replacing the op-amp and leaving the rest as-is) 
IC desoldered. On further checking there is no 10K , cap straight to opamp input. But on that line , some distance from the IC ,as space constraints , a diode topcode A7W. Probably a dual diode BAV99, checks out that way with DVM-D check. The common is connected to the input+cap and the diodes connected reverse-wise to + and - rails which are +5 and -7V, which I suppose clamps to less than the +/-10V of the specs, but fast enough? 
I just noticed in the 2122 datasheet
"When the supply is less than +/-10V, the maximum input is equal to the supply "
not supply voltage and 0.6V let alone any next to instantaneous overshoot voltage beyond that. Looks like another design flaw with this 2012 model
Replaced with a new opamp and noise generator has gone. I had mis-traced the path to the IC and the caps are directly connected to an input. I cheated and removed the 48V option, internally, as never used anyway. 
Does the 7mA limitation overide the 0.6V overvoltaging of an input? As the designer was very restricted in space (the "protect" diodes were some distance away) perhaps mutually reversed zeners in one SOT23 don't exist and he chose 2 diodes tied to the supply rails instead .
Audio amp probe p1 of U20 bad hash with no 
signal input. Replaced 2122 with 4580, NF 3 instead of 1.5nV
Problem gone now, opamp changed and 48V source disabled internally , 
traces one on top and one under the pcb to central sw pins.
2100,4072,072c,5218a,4556a
xlr to 2122 P1 and P7 op to gain pot and its associated electro
m/s for ground clamp fittings
3 thin pk each side minor pcbs
3 large csk pk end cheeks to top
Outer covers , narow vertical edge inside first , then force the wider rear edge into place.

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.


e-mail 
ncook246@gmail.co.....m 
 
 
 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/