I have found a source of the correct original type of step switch used in the Roland TR-808, and 
put them in the Parts section of my main site. You have to be really careful on how you remove the switch actuator so as not to break it, and the ribbon cable to the panel is very fragile leading to intermittent/no step 
button operation. The originals get gummed up and dusty inside, and they cannot be cleaned. I stock 2 types, the original, and a sealed variant (which has a different action). If you replace a switch I would suggest doing them all.
Tag Archives: analog
Original Oberheim SEM
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.
Roland VP-330 Service
Roland VP-330
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
Synthfool’s Opto-Key Installed
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.
Ace Tone Rhythm Ace
Ace Tone Rhythm Ace
I have an interest in old, analog, drum machines, and take them in for service. Sheldon brought to of these model FR-1 units in for service; one was in pieces, the other had gummed up switches, and was generally sad. The biggest issue I has was a lack of schematic, so if anyone has one
to share I would appreciate it. They also wired the boards into these units in a way that makes it extremely difficult to work on them. A full service was carried out on both, and both were fully re-cap’d as one had low volume, and the other excessive hum.
There was also a severe crackle on one unit that was traced to a 
noisy germanium transistor, that thankfully NTE had a replacement for (NTE103A). You had to adjust the bias afterward, but the pot fell apart on touching it, so that was replaced and all was well.
Roland Juno 60
This unit needed a deep cleaning session and service.It was disassembled and cleaned-up, with fluff etc vacuumed away.
The sliders and volume control had switch cleaner applied to cure the crackles, and key contacts were cleaned. One bank switch was not working, so I removed, opened it, and cleaned it. The battery was replaced, and FCO applied for dropping into manual mode (I have never had one come in that had 
this dealer applied; it addresses the fact that the power to the front panels goes through a couple of small connector pins, and this was insufficient, so direct power connections are added). Patches re-loaded, and unit put on burn-in test for a week.
Korg MS-20
Korg MS-20 Restored
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
Octave Cat Restored
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
Arp String Ensemble
Arp String Ensemble
I have had three of these come into the shop in the last 6 weeks, and the last of these was picked up yesterday by the owner. I’m seeing failures of rare and expensive divider chips such as the SAJ110 (QDIP pin layout but the only NOS parts I can find are DIP so an adapter socket needed to be made), and SAH190 can. The Mullard C280 series “tropical fish” striped capacitors are falling apart on touch (you see cracks appearing at the ends), but wherever possible I leave them alone in the signal path as newer mylar types may have a different tone (the C280’s are sought after by vintage pedal builders for there tone, which I guess means they are non-linear!).
An SAJ110 on one machine was sucking many amps (it measured 12 ohms) and had
caused the power supply to fail, on another it was a 
missing output. I recapped the power supply on two units, and for one of them we did a mass replacement of electrolytic’s as part of a restoration (and a sample of physically tired looking capacitors showed they were drying out with severely reduced capacitance.
The third unit had one dead key, and the owner had already changed a TDA0470 to no avail.
Looking with a scope the replacement chip was bad, and in fact it was ordered over Ebay from a vendor in China so who knows what it actually was. The original was put back in, and after much probing and deciphering of component layout the bug was traced to a bad resistor that had oxidized where the leg was cut off (they seem to have used some sort of pin flattening cutting tool in the factory which makes it hard to get components out), and then it had been re-soldered with a blob of solder over the top of the joint hiding the issue.
These keyboards sound great, but there are a lot of supporting components and rare chips that went into it so reliability is an issue.
Roland SH-5
Roland SH-5
This SH-5 came in with LFO-2 not providing modulation, and the led was dark, also the bender action was jumpy. The LFO-2 issue was due to a bad CA1458 operational amp which was replaced and restored operation. The bender is metal on this unit and we were seeing a little grittiness due to wear and lack of lubrication. I stripped out the keyboard control panel and cleaned, lubricated (pot cleaned and a small amount of grease applied to metalwork), and aligned it. Tuning and scaling was a little off on both oscillators, and was adjusted to spec.
