Portfolio of Repairs


Here are a couple of shots from the workshop: Workshop
Workshop amps
Mother and Son Reunion
Control cavity screening paint being applied
A moment in time in the shopI'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.



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. 

Kit built wah from BuildYourOwnClone.comThis 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.

Hendrix JH1-S WahJimi 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 trueHendrix JH1-S Wah bottom view bypass switch and used an isolated circuit to drive a pedal on LED.

Vox vintage V847 wah-wah in for repairVox V847 Vintage Wah-Wah This is the older battery only version from Vox and had a lot of stage use under its belt. The pot was seriously noisy and did not respond to switch cleaner. Vox vintage V847 wah-wah in for repair, internal viewReplaced 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; Pedals cleaned and repaired; ready for return to the customerthis was remedied by removing the jack and scraping through paint on the inside in order to get a good electrical contact.

Vox V848 Clyde McCoy re-issue wah-wah opened up to replace the stomp switchVox V848 Clyde McCoy re-issue Wah-Wah The customer had purchased this on Craigslist and found it to be not working. The stomp switch was out of adjustment and did not switch so was adjusted. The switch then worked but was highly intermittent in both off and on positions. The wires to the switch were a little corroded so cleaned and re-soldered, and tried to get switch cleaner into the switch. Reliable operation was achieved by replacing the DPDT switch (pedal has true by-pass) with a Carling switch from AllParts. This Wah has a nice range.



Electro Harmonix Double MuffElectro 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 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 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. Electro Harmonix Small Stone internal viewThese 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 PedalVox 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 jackVox Distortion Pedal internal view sockets. Once the sockets were tightened the pots wereVox Distortion Pedal cleaned up an working found to be loose and noisy. Pedal stripped, pots cleaned and tightened, and pedal cleaned up. Working fine now!


Ernie Ball volume pedal pre repairErnie Ball Volume Pedal The problem here is a common one with these pedals, the drive cord breaks. Getting a cord is an issue the South Bay Area as according to Ernie Ball, nobody within 30 miles of meErnie Ball volume pedal repaired 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 112 PlusFender 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.

This solid-state 100W amp needed new capacitors in the power supply.

B52-AT100 All tube headB52-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 350Gallien Kruger Backline 350.
This 175 watt bass amp was blowing fuses violently (so that the fuse glass was blackened). Gallien Kruger Backline 350 had a blown fuseThe 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-212Dean 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.Dean Markley CD-212 ading a series LED to the footswitch 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 residueDean Markley CD-212 clean-up 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 Dean Markley CD-212 switching j-fet'sswitch 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 with broken send jackMarshall 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 circa 1979Roland 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 transistorsRoland Jazz Chorus-1200 output 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 TwinKustom 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. Kustom 150 Twin internalsThese 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 BassSunn Coliseum Bass
This amp from the 70's had seen a lot of use and was popping when hot. I gave it aSunn Coliseum Bass internals 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 R1000 CyclopsCarvin 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 TICarvin R1000 Cyclops internal view 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 Bass AmpSWR 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 ChampFender 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 ampKora 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 powerKora Jupiter 60W + 60W amp power input 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 Kora Jupiter 60W + 60W amp internal viewfrom 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.


Alesis RA-100Alesis RA-100 This PA was dead on both channels. The issue was dry joints, especially around the volume controls. Two of the three activity LED's had also failed. New LED's and a run over with a soldering iron had this up and running in 30 mins.

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.>


Duct tape on a p-bass with bad electronicsFender 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. Fender MIM p-bass with active EMG's beautifully restoredThe 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.

Ibanez GuitarsTwo 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.