This Oberheim Synthesizer Expansion Module had been modified to the extreme, with over a dozen holes drilled in it for switches and jacks (did I mention that I’m anti mods that are harming to appearance, undocumented, and make the unit unreliable?). It no longer worked, and the circuit board and connectors had been damaged. The mods were removed (see tray of junk) and the unit put back to standard as tracks etc. were repaired, and things put back to where they should be. I made a cover piece from Formica to cover the holes in the case, and obtained the correct power switch and jack. The unit was then re-capped, set up, and is finally back with Jim, its proud owner.
Tag Archives: vintage
Roland VP-330 Service
This Roland VP-330 came in for general service. As is common with Roland synths, the gasket material had crumbled and a lot of debris was in the slider controls and needed to be removed. Its amazing that something that was designed to stop dust entering the sliders ends up doing damage (this makes me shudder because of the hours spent cleaning off the foam turned to goo on the Moog Opus 3, Rogue, and MG-1).
I cleaned out the sliders, disassembling a number of them, and lubricated them. The old gasket material was removed, and I used double-sided tape to attach stiffened black felt (from Michaels), which I cut slots in for the shafts. The end result is nice, and certainly improves over the look of the gaping slider slots. The felt will shed a bit of course, but the cure is better than leaving it the way it was.
I have applied felt to a number of Juno-106’s using variations of the attach method (double-sided tape, glue, attaching to underside of case, or to the top of the sliders). I would be interested to hear of any better materials (neoprene?), along with supplier.
Opto-Key MiniMoog Upgrade
The MiniMoog, along with many vintage synths, suffers from oxidization of the key contacts. It needs all keys to be pressed regularly to break the building oxidization, before it becomes a problem. The symptoms of the keys going bad are they become “squirelly”, i.e. multi-triggering, or dead due to not triggering at all. Another issue you see on keyboards is that as the keyboard generates CV from a resistance chain (1volt/Octave being common), any resistance in the contact alters the voltage out, thus frequency.
The folks at www.synthfool.com came up with an optical method of detecting key presses, called the Opto-Key. This incorporates a micro-controller in the design, making it possible for them to also add MIDI In/Out. Jason, the owner of this early MiniMoog, decided that as it was in need of service, he would ask me to implement Opto-Key, rather than continue with the key contact clean regime.
The keyboard was re-bushed while disassembled for the upgrade, and I can report that it works nicely. A service was also carried out, and some pots had to be opened in order to clean them and banish crackles. For reliability the disintegrating C280 “Tropical Fish” capacitors were replaced, the power supply re-capped, re-greased, and bridge rectifier replaced. All switches and open-back pots were cleaned, and the unit set to spec. Plays nicely now.
This MS-20 had sat in a basement for some 30 years, and was in a grubby state with corrosion on the jack nuts etc. One key was broken, and the power cable was damaged beyond use. I took it completely apart, cleaning everything, lubricating all pots and jacks. The caps were leaking, so a re-cap was performed. The customer obtained a replacement key from Japan, and I fitted that, along with a new power cable.
A benefit, and curse on the MS-20, are all the jack nuts. When you take the patch panel out, there is another set on a plate over the jacks to remove in order to access the circuit board. The benefit is that these nuts can be swapped for the outer ones, the washers flipped over, and then it looks nice and shiny. The MS-20 came in looking sad, and not making a sound, after restoration it looked and played great!
Octave Cat Restoration
I have done various Octave Cat’s and Kittens, from the original version, through SRM II. What they have in common is that they are tough to get going, and sorting out the keyboard contacts is always a major pain. This one though was the worst of the worst. It had been stored in a bad environment for many years, giving it corrosion and a bad case of filth. Worst of all though was that the bottom was missing, and the buss-bars/keyboard contacts were mangled, along with broken resistor packs. It was missing 5 of the j-wire activators, and all of the knobs and slider caps.
It was stripped, cleaned, and gradually rebuilt. I managed to straighten out the buss-bars and contacts, re-bush it, and hand-clean the keys. Everything was cleaned, and the sliders/pots/switches treated with switch-cleaner. Some of the switches had to be opened and deep cleaned in order to get them working. Electronically, some CMOS chips had failed and were replaced. VCO1 would not run at its lowest frequency, and I could see that a previous repair attempt had changed all of the suspect chips, plus there were a lot of component changes/ additions. I was fortunate in that another one came in, so I could compare and put it back to standard, and fix the original issue!
Life was then repeatedly cleaning and adjusting keyboard contacts, and fine setting it up until it worked reliably, phew! We purchased some knobs from Frys, and found that Sam at Syntaur has the slider caps. Doug at Synthparts thankfully had some of the j-wire acticators
Roland Juno 106
A number of these have come into the shop and for most of them it is a 80017a voice module issue. Roland put 3 chips (including the 3109) and supporting components onto a module, then covered it with a moisture sealing epoxy coating. There is a belief that the coating was required in order to protect surface mounted resistors from humidity change in order to stabilize their value, and/or protect their IP. This coating is thought to become conductive after 20 years or so. The only source of replacement parts is through chip pulls from scrap machines, and they are rare so costly. A typical symptom is a hanging voice, and/or crackling. I recently invested in a de-soldering station in order to get these chips out cleanly. The keyboard here was purchased on Craigslist by the customer for a good price but when he got it home he found it crackled badly, and a voice was hanging (you can isolate which of the 6 voices it is by putting the keyboard in test mode). For this unit it was not obvious which chip it was but careful testing showed it, and it could be verified with an oscilloscope. A replacement was obtained and fitted; all seemed well. After 3 hours of just sitting warming on the bench another chip started to crackle and had to be replaced. Speaking with the chip vendor this scenario is not unusual. The keyboard was not such a deal now that the cost of two replacement chips is factored in but the customer loves it and will get good use from it.
I have been using the acetone strip method to try and re-use a bad module before scouting a replacement. It takes 3 days of soaking and careful work to get residue out from between the chip pins. I silicone seal the module after washing it in order to seal the above mentioned resistors from humidity. This method has been pretty successful with crackly modules, but has not been good for completely dead ones, or where the VCF is drifting as we are looking at chip failures in those cases. It is a sad fact that all of these 800017a modules will eventually fail, and one unit eventually did have all 6 replaced. I have not tried the aftermarket replacements for the 800017a, but would advise folks to consider that. Also there are places that you can send the card and they will acetone strip all 6 modules; I’m not sure what the deal is when the strip does not work on a module though.
The bottom line is that if you are thinking of buying a Juno-106 then be aware of its issues and that they are not cheap to repair.
via This Old Synth – Vintage Analog Synthesizer Repair Portfolio Page.
This is the red version, and this one had the hand-grip. It had several issues, the most common of which was a touchy power switch (causes oscillator drift). I go 2 ways on this repair, either wiring across the switch so it is permanently on (no-go if batteries are being used), or order a replacement from TechnologyTransplant; the customer voted for the latter.
The switch arrived and was fitted. Switch cleaner was applied to all pots, switches, and sliders. I then re-soldered tracks around audio out and modulation connector, restoring switch operation and getting rid of crackles, and also re-soldered around the frequency and filter sliders as things were intermittent there.
The bender was only operating in one direction, the LFO push function did not work, and the unit needed adjustment as putting the VCO amount slider forward caused a frequency change. The last 2 items were cured by setting up the position of the bender on the pot shaft. The big issue was that the LFO switch was bad, and they did not make this repairable. I was unable to find a replacement (although having stripped that area out on a Juno-106 yesterday I see it looks similar). I managed to remove the old switch and modify it so that a micro-switch could be installed, and this works fine.
The unit was finally set-up to spec and sounds great!
Rhodes Mk1 73 Stage Piano
This unit was suffering from multiple dead keys, and things had been getting progressively worse. There were other mechanical issues, and once they were resolved the electrically dead notes could be focused on. By tapping the coils center pole 12 pickups were found to be dead, and on removing one it could be seen that the inner end of the winding had rusted through where it meets the pin. There is not enough wire left exposed for me to attach a bridge wire to, so the coil was deemed beyond repair. As I researched the Rhodes Mk 1 Stage 73 I found out just how big a problem that rust on the coils was, and that most used parts on Ebay etc are remnants of machines scrapped due to this problem, with statements in the ads like “rust cleaned off”. Continue reading
Arp 2600 with bad VCO
This just came in with “squirrelly” keys, and VCO 2 was drifting badly when warm. The keyboard contacts were cleaned, and VCO 2 was checked with an oscilloscope. The VCO was found to have drifting frequency output, but stable inputs. The 2600 had sealed VCO’s (these early modules were encapsulated in solid epoxy, later ARP ones had an epoxy sealing layer and can be opened and repaired) so an aftermarket replacement was ordered from CEM. The replacement part arrived after some months and was duly fitted. The keyboard contacts were cleaned, and the unit set-up per the service manual.
via This Old Synth – Vintage Analog Synthesizer Repair Portfolio Page.
E-mu SP1200 Drum Machine
This was purchased by the customer some time ago, and he had stopped using it due to boot problems. It had sat in storage for some time and gradually degraded. It was a missing large touch-pad button, plus the boot diskette had been lost. Without the diskette there was no way of finding out what else is required, and the customer went off to find one.
A boot diskette was finally sourced, and after many attempts it finally booted. The boot issue needed to be addressed, and it showed a need for pad button switch cleaning. The LCD back-light was also out. Continue reading