I'm at the point now where the number of vintage synth
and amp repairs undertaken means that I cannot keep this log up to date. I
hope that the information here has helped other repairers and I welcome
their contact with questions. My main focus has become
This Old Synth,
which services vintage analog
synths from the 60's, 70's, and early 80's.Pedals
Wah
I have spent a lot of time working on Wah pedals. The most common problem is "scratchy sound" due to the Wah pot. These are special ICAR taper pots with a fitted gear, a common variant being the 100k Hot Potz I. You can still get these pots but Dunlop is guiding folks to fit the newer sealed (which also means more expensive!) Hot Potz II. Some of the non sealed pots can be restored with a shot of switch cleaner, and I always try that first. Switch cleaner seems to work on a lightly used pedal that has been idle for a while, worn pedals invariably need a new pot.
This is a
kit built Wah from BuildYourOwnClone.com that
did not work. A new Wah switch and changing the values of a couple of
resistors brought it to life; sounds really nice and the pots enable you to
dial in your tone.
Jimi Hendrix Special JH-1S
(these were built to Hendrix specs with a
special inductor and 470K Wah pot which moved the Wah tone to lower
frequencies). I fitted a Hot-Potz II, true bypass switch (true bypass
removes the tone sucking load presented to the amp input when the pedal is
off that is a problem with standard Wah pedals). I used a 3 pole true
bypass switch and used an isolated circuit to drive a pedal on LED.
Replaced
the pot with a NOS 100K Hot-Potz-I to match the original, and
cleaned/lubricated the pedal; the pot noise was gone. On final test I
found the pedal to be picking up radio signals due to a poor input jack
casing connection;
this
was remedied by removing the jack and scraping through paint on the inside
in order to get a good electrical contact.
Distortion
Electro
Harmonix Double Muff. This pedal had a faulty output jack, nice simple
repair! I'm surprised this pedal is not more popular as it offers
distortion and then more distortion on top of that; maybe they should have
added a second stomp switch to add the extra distortion, rather than a
slider switch.Electro Harmonix Big Muff Pi NYC This pedal was intermittent and the customer did not like the tone. The intermittent problem was due to a faulty volume pot, and a genuine EH part was obtained from Small Bear electronics and fitted. We then replaced the transistors and tweaked capacitor and resistor values to give the tone the customer wanted.
Electro Harmonix
Holy Grail The customer was fed up with EH wall-warts for each of
his pedal, so the task here was to drill the case to accommodate a Boss 9v
power jack and fit it. This is a sweet sounding pedal! Electro Harmonix Big Muff This was an older pedal with two issues, the stomp switch was bad, and the pcb tracks were open near the pots making it fail as the pcb was flexed. Resolved the issues and put the pedal back in service.
Electro Harmonix Small Stone
This is a vintage
(1979) version 2 (release j pcb) small stone that I picked up in a faulty
state. I diagnosed the problem to be a failed Operational Trans
conductance
Amplifier.
These are type CA3094 and have been obsolete for many years, so a hard to find part. I obtained one from Small Bear Electronics and this phaser is up and running, sounding sweet! 
Vox Distortion pedal
This is a fairly mild distortion pedal that has seen a lot of live on stage use. It was a mess of howling, crackles, and feedback. The initial
problem was bad case earth and loss of signal ground due to very loose jack
sockets. Once the sockets were tightened the pots were found to be loose and noisy. Pedal stripped, pots cleaned and tightened, and pedal cleaned up. Working fine now!Volume
stocks them... so you order, pay a high rate of postage, and wait. The $4
part arrived and was fitted in 20 mins (a bit tricky fitting this cord but
doable)
Guitar Amps
Fender Princeton 65 This amp was dead and had a broken tone pot shaft (knob lost). It was dead due to a simple blown fuse and testing did not turn up a cause for failure, so just one of those things! During test the volume pot was found to be crackly and did not respond to switch cleaner. Eventually found genuine fender parts online for this amp and restored it to its former glory.
Fender Princeton 115 Plus This was basically working but the hum was so bad it was totally
unusable. The main capacitors had become dry jointed and reflowing the solder restored full operation, and no parts required.B52-LG100A. This solid-state 100W amp needed new capacitors in the power supply.
B52-AT100.
The AT100 is a 100W 3 channel tube amp with quad output stage. It
was non-operational due to an issue with one of the tube bases which was
replaced. The reverb tank had fallen apart and on replacing it the driver
controlling operational amplifier was also blown. Parts replaced. This is
a loud amp with lots of control over your tone. 
Gallien Kruger Backline 350.
This
175 watt bass amp was blowing fuses violently (so that the fuse glass was blackened).
The main power supply was found to be badly dry jointed, especially around the main capacitors.
Re-soldering and replacing the fuse with the correct slow-blow type restored operation. I liked using this amp and was sorry to see it go!
Dean
Markley CD-212 tube combo The issue here was with the drive
channel switching. The led indicator in the pedal was missing and was not
found inside the pedal. Wiring reworked which got the switching going at
the amp according to the channel LED's on it. Attempting to put a new LED
and resistor in parallel with the switch per the effects loop caused the
amp channel indicator's to show a partial switch.
Scoured the web for schematic's for this amp and found some partial poorly
drawn ones, but nothing on the footswitch. The boards have a number of
issues reported with this amp not switching correctly (or at all) due to
J-Fet failure (the J-Fet's are used as a switched short across various
volume etc. controls in order to mute sections of the amplifier). I decided
to rewire the switch and put the LED in series with it which worked as far
as the channel LED's were concerned. On test the drive channel was found
to be very weak on its depth of distortion; the clean channel mix for the
distortion channel was not working, and various pots were very noisy. Amp
stripped out, vacuum run over inside and residue
of a liquid spill cleaned. Foam cleaned knobs and panel and got over the
majority of the pot crackles with switch cleaner (NOS pots for this amp
are hard to find BTW). Pre-amp tubes were a little touchy, cleaned tube
bases (a new set of tubes at some point would be a good thing). Amp was
now working reasonably, apart from the drive section clean volume mix and
low overall drive. Checked the channel
switch
FET's relevant to this and found two of them to have leakage resistance.
Obtained 2 new 2N4393 J-FET's (these are rare and obsolete, but thankfully
J113's are an equivalent and could be found locally); fitting them
resolved the drive channel issues. 
Marshall
JVM2000 DSL100 This amp was a nice simple repair, or should have
been. The effects send jack was broken (but still worked). These jacks are
plastic and the difficulty is in getting parts, especially the nut which
had been lost. The correct part was ordered but had more pins than the
original. Tracing the connections showed that only 2 pins were used so the
extras were cut off. 
Roland
JAZZ CHORUS-1200 This is a circa 1979 stereo output amp
that came in for blowing input fuses. The problem was traced to the pair of
output transistors on one channel being shorted between emitter and
collector. These transistors
(2SD845) became obsolete many years ago. Thankfully one of the listed
alternatives had a later equivalent from NTE (also an old device). A trip
to two different Fry's stores got me the last one from each (NTE92).
Checked all other transistors and off load voltages, ok. Cleaned the pots
and jacks; amp sounds fine now.
Kustom
150 Twin Paul contacted me to see if I could repair his 40 year
old Kustom amp. He had been having great difficulty getting it repaired at
other shops as they wanted a premium for diagnosis prior to repair. It was
a fairly difficult amp to work on due to the use of the chassis for the
negative rail. I found a schematic for a similar amp and diagnosed that
although they measured OK, the input transistor for both channels had zero
gain.
These
transistors are long obsolete, and the first line replacement was long
obsolete too. Searching the web a found some NOS replacements for the
first line replacements and fitted them. All the pots were cleaned and the
amp was back alive. Paul was so happy he kindly sent me a citation, thank
you Paul!
Sunn
Coliseum Bass This amp from the 70's had seen a lot of use and
was popping when hot. I gave it a
general cleanout, replaced a broken power switch and double-ganged volume
control, after which I could fault find the popping sound which was due to
a socketed transistor which was loose.Fender Twin Reverb Re-issue This amp came in for popping noises when hot. It had been to another local repairer who said it was working as designed, and charged the customer leaving him disgruntled. I ran it on the bench for a couple of hours and the described symptoms emerged. Using an oscilloscope I positively identified a bad ECC83 as the faulty item and saw that the problem moved with it when I swapped tube locations. Fitted a matched pair of EH pre-amp 12AX7's and ran clean for 4 hours. Customer is delighted!
Carvin
Cyclops R1000 This is a 500W bass amp and it had gone silent
after issuing smoke. The problem was traced to shorted 4558 Op Amps on the
output board which were dragging down the 15v rail. Replaced both op amps
with better quality TI
parts from Anchor Electronics. On test the amp sounded scratchy and the
15" 4 ohm Carvin Eminence speaker was found to have a rubbing cone.
Customer (Gary) had a spare 8 ohm JBL speaker which we fitted until he can
get the original re-coned. Amp sounded great on keyboards and will be used
for that in the future. 
SWR SM400S
Customer
purchased this bass amp off of Craigslist with one deal 4*10 cab he got
with it was buzzy which we isolated to one of the speakers, he is off to
get it re-coned.
Fender Vibro Champ This vintage 70's amp came in
with low sound and was noisy. Previously a repairer had removed the tube
rectifier, converting it to solid state. This resulted in higher than normal voltages which stressed other components.
I cleaned the tube sockets, removed the solid-state conversion, and
replaced the cathode bypass caps. The power dropping resistors were
replaced with ceramic types and a new set of tubes obtained and fitted.
The bias of the output tube was set to spec and the amp performed as it
should.Hi-Fi Stereo Amps
Kora
Jupiter 60W + 60W Stereo Block This came in with the symptom:
Distorted left channel (crackles and pops), then it went dead. This is a
high-end tube amp from the Kora company in France. The "deadness" was
cured by obtaining a new power
input/fuse/switch/filter assembly. The original was a 3amp filter part
with screening. The nearest equivalent I could get from Mouser (same
manufacturer) was a 6amp filter part, so better, but it lacked a screen. I
moved the screen from the old part to the new one and installed it. Under
test I fount that the crackle heard on the left channel was due to tube
bases. I cleaned and re-soldered the bases but they are fragile individual
(meaning that they are individual gold socket pins, not held together by
an insulated base. This is not desirable as heat
from
the tubes gets to the pcb scorching it, and any rocking etc. as tubes are
reseated is a direct stress on the solder joint/pcb lands - so reliability
will continue to be a problem) pins, and some of the actual spring
contacts were staying on the tube pins when removing tubes. After this
work the amp was working fully. The need to replace the tube sockets was
discussed with the customer who felt that the amp would only be lightly
used now and if it fails again we would replace all sockets and install a
fresh set of tubes.PA's
I have decided not to work on any more PA's due to the density of power transistors in a cramped space and an inability to drive these hard with a speaker rather than resistor load.>
Guitars
Fender MIM Precision Bass
with EMG active pick-ups. I got this on
Craigslist List as an 'as-is' non working project, and boy was it in a mess. The electronics were a mess of bad soldering and faulty pots and connectors, and the pick-guard had a hole drilled through with a battery held in place on the guitar body with duct tape.
The
whole thing looked sorry and was set up terribly. I worked through all
issues, replacing parts, cleaning duct tape off, lemon oiled the fretboard,
new strings and full set-up. Now, apart from a couple of paint chip dings
on the back where you can't see them, it looks fabulous. It plays well now
and has a great solid tone. This bass just sold through Guitar Showcase
who reported that the customer was delighted with it.
Two
Ibanez guitars
found their way into my shop today, a nice blue Soundgear Gio GSR100 Bass, and a
black RG 120 guitar. These were both in a world of hurt,
and cosmetically filthy (why do folks put stickers on guitars? I would
expect it was to cover damage, but when you finally clean all the goo off,
the best paint on the guitar is where the sticker was!). These low end
Ibanez guitars are fundamentally sound but have cheap electronics and poor
screening. A clean of the guitar and pots, tightening loose just about
everything, and new strings and full set-up got these units back to
presentable and usable condition.