ARP Soloist meets 3D Printing

This is a ARP Soloisist Slider Fixrare original ARP Soloist (before the ProSoloist or DGX). A lot or restoration work was done on it, but one issue remained; the slider shafts were all broken at the point where they exited the case, and the slider caps were long gone.

The sliders are the same type as fitted to the ARP 2600 and moog SonicSix, amongst others. This is a hard to find part, and here we have 4 sliders with 3 different values. ARP Soloisist Slider FixSometimes you can find replacement shafts for these on Ebay, but nothing was listed at this time. After much head scratching I decidedARP Soloisist Slider Fix to raise the existing sliders by 8mm, and needed some precise flat blocks to do that with. I came up with a design and after many attempts (that’s 3D printing for you!) I produced a nicely printed set.

ARP Soloisist Slider FixThe sliders were removed, opened, cleaned, re-greased, then set on the blocks which I had super-glued to the ARP Soloisist Slider Fixcircuit board. There were locators in the blocks for the original slider mounting, so when the wiring was added using a heavy gauge wire extension, all was firm and true. I re-assembled the unit and added some Omni-2 style slider caps I had previously printed. All working and crackle free. Next move was to tune and scale it.

One item remains on the Soloist, the after-touch used conductive foam which was known to only last 8 months, and had all by disappeared on this 1975 keyboard. I would have liked to have got some modern strain/pressure sensors and tried to make a solution, but the owner decided to defer that to another time.

MTG Turbo CPU + MIDI + CV

 

MTG Pro One Turbo CPU

Turbo CPU

I’m generally against modifications.  I have seen too many vintage synths spoiled by badly drilled holes that hold fragile switches, connected through an “umbilical cord” to undocumented perf-board based mods made decades ago, and then more wires soldered to the circuit boards. Working on the gear becomes difficult as these wires are holding the case to the cards, and of course wires fatigue and come away, and you have a challenge as to where they once went, and how the mod is supposed to work.

 

CV WiringI do see the benefits of a good MIDI implementation, and I have come across a couple of MIDI kits where the designers have come up with good clean designs that can be unplugged for service. In this entry I talk about the Turbo CPU upgrade kit from MTG (Music Technologies Group). Grant runs the MTG and I have found him responsive, friendly, and helpful so recommend doing business with him.

In a different post I will talk about a nice MIDI solution for the Roland TR-808 from another vendor.

Installed MIDI interface cardAll of the instructions are available to download from MTG (http://www.musictechnologiesgroup.com/index.html), so you can see what is involved. I’m on the list of experienced installers and would be happy to implement this for you, but note that I am not a reseller so you have to purchase the kit from MTG. Turbo CPU a simple removal of the CPU and install of the Turbo CPU module.

Drilling holes for MIDII think most folks would be interested in the MIDI interface which for a solid installation does mean drilling the base of case to mount the MIDI interface card, and the back of the case for the MIDI connectors.

I prefer the look of the MIDI connectors squeezed between the lettering, and made some identification labels for the MIDI ports squeezed between logosMIDI ports. Both customers for this kit wanted the MIDI interface, plus the “DIY” CV interface which adds a tiny MCP4728 chip to the v2.00 MIDI board (I was fortunate that the MCP4728 was pre-installed on one unit, but had to order it from Mouser for the other.

Alternative MIDI connector mountingFine soldering skills are required to install this chip as it is surface mounted, so ask Grant if you can have a card with the MCP4728 pre-installed when you order :-). The DIY CV interface gives you MIDI control over 4 CV wires and is a great addition that requires no trace cutting or case butchering, so I like it!

MIDI interface with plug connected CVFor my implementation of DIY CV I installed a connector at the MIDI interface card for the 4 wires so it could be disconnected for service.

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 www.syntaur.com).

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.

Original Oberheim SEM

Oberheim_SE1This 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, Oberheim_SE1_2undocumented, 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 Oberheim_SE1_3standard 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

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.