Linn 9000

Linn 9000 1My customer won this working unit on Ebay, and agreed to pick it up from the seller. Between the end of the sale, and it being picked up the seller decided to get his tech to replace the batteries as they were leaking. Following this it would partly boot but hang, not good! Thankfully a heavy discount was negotiated to cover repairs, and in it came to my shop.

I have not worked on one before, and I was amazed to find it Linn 9000 3is based on the first IBM PC, ISA bus and all. This one had a lot of Forat mods, including the SRAM256 card which I have read is a favorite for folks to blow up by inserting backwards. I checked the batteries that had been fitted, and was only getting 2.4v, and one read shorted. I purchased new lithium batteries and a charger which confirmed that one was indeed Linn 9000 6shorted. New batteries were fitted. Powering on found the screen blank, and this was traced to the CPU being stuck in reset. The transistor between the batteries and this line was bad, and replacing it released the reset. Checking the CPU clock found it running less than 1/10 correct speed. The osc chip SN74LS04 and its socket were badly corroded by the battery acid; parts replaced and clock working correctly.

We were back to it hanging, but things were now solid as the battery/acid damage was out of the way. Address line A6 was found to be low amplitude, and the SRAM256 card was Linn 9000 4dragging it low. Removing the card put the 9000 into a mode where it was looking for the SRAM 256 card (Forat firmware and card), so it would not come up. From the schematic, -12v would go to A6 on the SRAM card if it were reversed (surprise!). I traced the shorted A6 line to a PAL on the SRAM256 card, and socketed the chip. Lifting the PALs leg Linn 9000 7enabled the card to be plugged back in. Bruce Forat was contacted for parts, but by the time he came back with a price I was well into reverse engineering the card fitted detection in the PAL using a logic analyzer and 8080 disassembler. Clearly the address decoding part of the PAL was still good as after zapping the code that looks for the card everything came up. The customer wanted to go this route as he wanted to see what else was bad on the 9000 (i.e. was it a write-off) before spending more on it. As the PAL is socketed he can eventually order the PAL from Bruce, and fit it along with the original firmware eprom.

Linn 9000 2Testing showed the floppy controller was bad, and a chip change fixed that (did the cable get reversed at some point?). Last thing was to replace the screen with a more modern high contrast led back-lit one. Customer sent me a YouTube video of it in action that night, he is delighted!

Moog SonicSix

SonicSix1I’ve completed a few of these now, and must admit to a little trepidation when they come in as this synth was clearly made for education use (everything is squeezed into a SonicSix2plastic suitcase with no ventilation holes, or easy access to pre-sets for set-up etc.). Setting it up is difficult to say the least, and like others in blogs I have read, just got it to scale on both SonicSix3oscillators with minute adjustments. The original pre-sets are of very poor quality, so I replaced the majority of them; thy used very low ohm values and did not get a nice sweep on adjustment, so multi-turn replacements would be good, but space and access is an issue.

SonicSix4The main issue was that it did not scale, and sounded like hell. The root cause was the -15v regulator where the 723 regulator chip was holding it at -23v. Thankfully no other chips have died (yet) due to this. One of the rectifier diodes was also bad, so there was a lot ofSonicSix5 hum from that, but after replacement of these parts things settled down. The Mullard C280 “Tropical Fish” caps were falling apart, so they were all replaced, alog with the can caps. Next move was to service all of the pots/switches, re-bush the keyboard, and (struggle with the) set-up. Jim was delighted, which makes the effort worthwhile!

Moog Multimoog

MultiMoog1Back on my favorite brand, Moog. There is a steady stream of MiniMoog’s through here, which is my overall specialization, but I do not report on them as it is MultiMoog2mostly the same issues that strike them. This is a Multimoog, which customer Jim scored along with a Sonic Six. This one had no output, and the key bushings were shot; the seller reported that it worked when he put it it away in the closet decades before!

MultiMoog3It cleaned up nicely, and the bushings were replaced with each key cleaned by hand. The buss-bar plastic mounts had gone brittle, so I had to make some parts on the lathe, and rob a parts keyboard to resolve this. The lack of output was due to a dead CA3080E MultiMoog3transconductance amp (common bug). Pots and switches were gradually worked with switch cleaner until they performed correctly. The buss-bars had to be removed in order to get the oxidization off them and the contacts. Unit was set up and played nicely. One surprise for me was that the after-touch was fully working, pity the design of this severely limits key travel.

Crumar MultiMan-S

CrumarMM_6This unit had been powered off for many years, and although it looked nice once dusted off, oxidization had done its worst on key contacts, made sliders crackly etc. The brass section was not working, and the pitch slider was broken.CrumarMM_2 - Copy I could not find a source for sliders, and ended up grafting a metal shaft onto the pitch control. The sliders are of a closed and sealed type, but thankfully (and surprisingly to me)  injecting switch cleaner into screw holes in the slider cases banished the crackles.

CrumarMM_4 - CopyInvestigating the brass issue revealed cracks in a circuit board from impact, with a poor repair attempt in the past. I wire jumpered allCrumarMM_5 - Copy bad and suspect circuit board traces such that if the crack grew a little then it would still work. The final issue was key contacts, and in the end I had to remove the buss-bars in order to clean them CrumarMM_1which is a major strip-down effort. The contact springs were really bad and had to be repeatedly treated using isopropryl as a cleaner. The results are pretty good, but the only way to get it to 100% would be to find new springs. Customer just loves it!

March of the Juno-106

Juno101_1I do not know why, but March saw a stream of Roland Juno-106’s. Voice module failures were a commonJuno101_4 failure item, and I spent a lot of time running modules through the acetone bath. The acetone bath method is not a cure all, as once a chip is damaged by the epoxy coating shorting it, then it is bad of course. The acetone strip method is a Juno101_5good preventative maintenance item though. I have been suggesting that customers look at services such as the synthspa as they say they will replace bad modules as part of their stripping Juno101_8process, and I cannot compete with that as I’m having to purchase reclaimed modules for repair.

Juno101_2One unit had been dropped which resulted in a lot of broken keys, and a distorted panel. Another unit suffered a broken pitch bend lever, and another the plastic push “spring” for VCO modulation (both of these parts are available from Sam at

Juno101_7Loss of patches due to battery failure was seen on 2 units, so I’m recommending replacing the battery now even if the voltage is good. The bad side of this though is that the patch loading tool for the Juno-106 only does a patch at a time (no sysex load/dump capability), so you have to do the tedious patch edit and save for all 128 patches.

Juno101_6Two units were highly touch sensitive, and this was due to multiple bad sliders. One issue leading to this is oxidization due to a bad storage environment, another is the crumbling gasket Roland used falling into the slider. The cure is to remove, open and clean all sliders, remove old gasket material, and make a gasket from stiffened felt. While I have been in this area I have also been replacing intermittent patch etc. switches, and really they should all be done if one fails as dust getting into the switch is the culprit.

A final issue seen is with the bubble contact strips failing and giving intermittent keys. On the Juno I seem to be seeing other factors such as a liquid spill (on the Korg Poly6/61/MonoPoly they just plain fail).

All of this is leading me to making the standard service for the Juno-106 include front panel switch replacement, slider removal, open, clean, and lube, gasket removal and replacement, battery change, and optional module acetone strip. This is all labor intensive so not cheap, but it would get the keyboard running nicely again, and last another 20 years.

Roland System 100 Model 101

System100_101_1  This unit shipped in and per the customers description, had a dead keyboard and lots of slider issues. TSystem100_101_4he sliders in here are rare, and the worst one was a dual slider type that could not be found anywhere. All sliders were found to be gummed up with old grease, dust, hair, and other debris. The unit had to be deep cleaned, and all sliders opened, cleaned, and lubricated.

System100_101_6The keyboard was giving a large negative CV out, so off the audible scale. The customer said it worked until he tried to clean the contacts due to a few bad keys. What he had done was to overSystem100_101_2 aggressively clean it such that a lot of the CV contacts were dis-formed and resting on the gate bus-bar. These were straightened out, but the majority of keys were then intermittent and badly triggering. Closer investigation revealed that the contact wire that is welded onto the key spring was either missing, or broken at one end such that a consistent on and off point for the trigger and gate could not be achieved. Contact sites were rare and expensive,System100_101_3 so it was a case of using the good trigger contacts from some of the contact assemblies to make complete good ones, then salvaging assemblies from my spares RS-09 (fewer keys) to fully populate the 101. This was a LOT of work, but the keyboard is fully functional now and the owner is delighted.

System100_101_5One other note here is that if someone uses the wrong tool on a ferrite oscillator coil slug as a previous repairer did on this one it will crack and not be adjustable in the future.

Roland TR-808 Step Switches

Roland_step_1I have found a source of the correct original type of step switch used in the Roland TR-808, and Roland_step_2put 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 Roland_step_3button 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.

Rack-mount Synths

MKS_70_1I often get asked to work on rack-mounted synths. Unless they are very early units I have to turn them away as without factory extension cables (which I do not have for MKS_70any model) you can’t get the crammed in cards out on the bench in order to work on them. I this post you can see the amount of stuff that has to come out in order to perform a simple battery change on a Roland MKS-70.

Roland VP-330 Service

Roland VP-330

Roland VP-330

This Roland VP-330 came in for general service. VP330_5As 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 VP330_2I 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.

VP330_4I 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

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 came up with an optical method of detecting key presses, called the Opto-Key. This incorporates a micro-controller in the Stripping the keybed for re-bushingdesign, 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.Removing the keys

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 View of Opto-Key controller and optical sensorshad 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.