Saga Musix' demoscene blog.

Synthesizer Repairs November 7th, 2022

I've been building my studio with lots of vintage synthesizers for more than ten years now. There are some common faults this old hardware develops with age, many of which are easy to fix with basic electronics knowledge and basic soldering skills.

Often these repairs require purchasing spare parts, which can be rather expensive when bought from stores specialized in vintage synthesizers. Of course I know that they need to make a living, too, and sourcing the parts, figuring out what are the correct and best parts to sell can be a time-consuming process. If you want to be 100% sure that the parts you buy will fit your synthesizer, buy from these stores. Otherwise, here is an assorted list of spare parts I bought over the years that can serve as cheap and suitable replacements.

Service manuals

Tactile switches

Ah, the bane of every synth owner's life. One of the most common parts to break on synthesizers. You know it's time to replace them when a soft touch is not enough to trigger the buttons anymore. Better replace all of them in one go, as more and more of them will fail over time and they are really cheap.

Without further ado, here are compatible tactile switches that I have bought over the years:

• Roland D-50, Roland PG-1000, Kawai K4: TE Connectivity ALCOSWITCH 1825910-6
• Roland JD-800: You can get a set of buttons for a fair price at Vintage Synth Parts. The JD-800 uses three different types of switches. The third type, used for LFOs, filter mode and other patch settings is not part of this set, though.
• Roland R-8: Omron Electronics B3F-6120. They are a bit on the expensive side compared to the previous items. I have a feeling that the switches used in the D-50 might also work here, given that there are extra holes in the PCB for switches with four legs, but maybe the missing ground pin would cause issues.
• Roland JP-8000: TE Connectivity ALCOSWITCH FSM4JRT (untested, will most likely work. again the switches used in the D-50 might also work here if the PCB has holes for switches with four feet, which I have yet to verify. They might also work as replacements for the arrow button tact switches in the JD-800.)
• Kurzweil K2500: TE Connectivity ALCOSWITCH 1825966-1
• Behringer BCR2000: TE Connectivity ALCOSWITCH 1825967-1 (I assume that the BCF2000 uses the same type of switches)

Capacitors

Roland's SR-JV expansions ROM cards are known to contain a capacitor that may leak or even explode with age. There are many suitable replacements with higher margins than the original capacitors Roland put on those boards. I used Nichicon GYB1E101MCQ1GS as a replacement.

EL-backlit displays

Electroluminescent display backlights get dim with age. Typically your options are to replace the EL foil to revive the original, or to replace the entire display assembly with a new LED or OLED display. This also has the advantage that it avoids the high-pitched noise that you can often hear from the EL display's inverter, at the expense of modifying the look of the synthesizer. Finding a suitable replacement display can also be a tricky task at times. Displays advertised by their seller to work with a specific kind of synthesizer are often overpriced.

For my Yamaha TG77, I opted to replace the entire display assembly with an LED-backlit display that is guaranteed to work with the synthesizer. Yes, it's probably four times more expensive than finding the same display on eBay (okay, maybe twice as expensive after customs duty and shipping), but I think the price is still fair and it comes pre-assembled with clear instructions and no soldering is necessary, which saves some work. The display is available in various colour schemes, the one linked above is probably the closest to the original colour scheme of the synthesizer.

Encoders

The "alpha wheel" on my Kurzweil K2500 broke down, no longer producing a nice reassuring click with each turn, spinning freely instead. I could not find a drop-in replacement, but the Grayhill 25LB15-Q encoder gets close. The shaft is too long and a bit too thick, which can be fixed by cutting it a bit shorter and using sandpaper and a file to make it a bit thinner. Make sure to keep the "D" profile of the shaft so that it slides nicely into the hole inside the button. When doing so, constantly keep checking if the shaft fits into the button so that you don't make it too thin - otherwise the button will not sit firmly on the shaft anymore. The little hole in the lower plastic part of the alpha wheel is also not quite in the correct position for the little stud of the encoder, but that hole can be widened a little bit with a sharp knive or scalpel so that it fits.

This replacement is a bit more "clicky" than the original part and thus requires slightly more force to use.

Memory

Ah, my speciality, you could say! Together with my pal dojoe, we built and sold Roland memory card replacements (M-128 / M-256 / M-512) that are backed by non-volatile MRAM. Unfortunately we no longer sell them, but you can build your own, as the card design is open-source.

In similar fashion, I teamed up with WaveReX to develop a replacement for the ME-1 memory expansion for Kawai K5000 synthesizers. You can get it from the WaveReX shop.

Looking for Ensoniq or Kawai memory cards? They are even rarer and even more expensive than the Roland cards. The good news: These cards are just rebranded Fujisoku 38-pin SRAM cards, and sometimes you can find those OEM cards for much lower prices (and by that I mean less than 30 Euros). Just make sure it has the right capacity - a card type starting with BS8 indicates 8KB of SRAM for example, equivalent to a Kawai DC8, and a BS64D1-B card would big enough to be compatible with any Ensoniq or Kawai synthesizer.
Some sellers refer to these cards by their US patent number ("uspat4780791"), as this is usually the only thing printed on those cards apart from the brand name and serial number.
German users may also have some luck by keeping an eye on "Telekom Connex Memory Cards", which are also just rebranded Fujisoku cards.

Don't pay outrageous prices for the Kurzweil K2500 PRAM option. Build a cheaper one yourself: dojoe got you covered, again.

Speaking of the Kurzweil K2500 (and the K2000): Revision A-J of the K2500 (and all K2000s) use 30-pin SIMMs for sample RAM. If you want to max it out, you need to go with 16MB modules, which can be expensive to find. Some years ago I found this kit on Amazon, which was comparably cheap at the time (less than 30 USD), but it has since gone up in price. Still, it is probably one of the cheapest brand-new options that you can find. Owners of the later K2500 models are lucky as they take 72-pin SIMMs, which are much easier to find in the required capacities.

ROMs

Software / Patches

Ensoniq sadly is one of the few once-big synthesizer manufacturers that are no longer in business. This means that a lot of great resources were lost in time. However, the Web Archive snapshots of their download pages are pretty complete, so a lot of the orginal material such as demo song SysEx dumps for the SQ series can be downloaded from there.

A lot of older Kurzweil material is still downloadable from their website, so don't get scammed by people selling original Kurzweil floppies for your K2500 for outrageous prices - you can still download various operating system versions from the Kurzweil website. The contents of their old FTP are currently unavailable, which might be a temporary issue, but even if it's permanent, they can be downloaded through a Web Archive snapshot.

Belts

I recently got my hands on a Yamaha DMP7 (their first digital mixer), and apart from a completely depleted soldered-in backup battery that I replaced with a CR2032 battery holder, the motorized faders were barely working. Obviously this was due to worn-out rubber belts. I couldn't find any resources on the correct size of belts, which is really unfortunate: As cassette players and optical drives have somehow went out of fashion for some reason, replacement belts for these kind of devices are often expensive. Either you pay multiple Euros for a single belt of the correct size, or you end up buying a hundred belts for 10 to 20 Euros, but there's only one or two belts of the required size, so the final outcome is still expensive. Most of those kits lack the small belts required for this repair, anyway.

Luckily I found that German electronics shop Pollin had a selection of belts that could potentially fit, with a convenient price break point at 10 belts - and the DMP7 requires 11 belts. The belts that I linked have an approximate diameter of 18mm, or 30mm when stretched. I think this might be a bit too tight, but the next bigger option (22mm / 35mm) is definitely too lose. If you have the possibility, you should try to source belts inbetween those two measurements.

Assorted repair resources

• Check out my previous blog entry on cleaning Roland D-50 key contacts.
• If your Roland JD-800's keybed is in a sad state due to the red glue issue, this video by Scott's Synth Stuff could be interesting as a few options such as replacements for the rubber bushings are discussed there. Someone else fixed the keybed in mine before I bought it, so I cannot comment on the repair.
• Some rubber bushings were missing on the keybed of my Kawai K4, so some keys were rattling and moving left and right. I tried the method suggested in the previous bullet point and used two layers of silicone tubing (4mm inner diameter, a thicker outer diameter might have helped with only requiring one layer), and it did indeed work.

Untested / planned fixes

The Yamaha AN1x display backlight can get dim with age (although I do not remember it ever being brighter than it is now...). The backlight consists of 2V LEDs, which narrows down the options a bit. Some replacements are discussed on the Syntaur forums.

My Roland PG-1000's backlight is still okay, but it has some annoying high-pitched noise coming from the display itself. Since the original display looks absolutely gorgeous, I'd like to keep it stock if possible. I will need to figure out if replacing the EL foil or other parts of the display can fix the issue, and will update this blog post accordingly.

I also want to replace the slider dust covers in various synthesizers, as the foam used in those covers started to disintegrate or already has done so. Stay tuned.

Final words

That's all for now. I will add more material in the future when I need to do further repairs.

Last updated: 4th of December 2023