Synth Defects - Ticking Time Bombs

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Synth Defects - Ticking Time Bombs

Postby coastalscrub » Mon Feb 23, 2015 5:17 am

There are documented problems with a handful of synths where leaving the problem unaddressed causes major damage to the synth.

- Korg Polysix - the original NiCad battery leaks and causes catastrophic corrosion to circuit board.

- Roland Juno 106 / MKS-7 / MKS-30 / HS-60 - the voice chips have an epoxy coating that eventually short the chips resulting in dead voices.

- Roland JD-800 - the weights in the keys are glued in with a red glue that deteriorates and cover the keybed with goo. Because there aren't other keyboards with the same keybed, a replacement has to be purchased directly from Roland for around $300.

Not catastrophic problems but there's the membrane button problem in the Akai AX-80 and the keybed problem in the Ensoniq VFX.

Any there any other synths folks should be concerned about?
Last edited by coastalscrub on Mon Feb 23, 2015 7:02 pm, edited 1 time in total.
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Re: Synth Defects - Ticking Time Bombs

Postby Alex E » Mon Feb 23, 2015 7:04 am

Trying to think of some... I know about most of 'em.

The Roland JD-800 has the same keybed as the JV-80, D-70, U-20 and a couple others. If you can find a donor machine that hasn't had those weights fall out yet, you can swap the keys out. Cleaning that mess off the contact strips is another story.

Another issue that comes to mind is how the Mono Evolver/Poly Evolver encoders can wear out over time and skip values. Same with the Prophet 08. Such a drag, cause they're great synths. DSI ended up making those with pots instead of encoders, and offered an upgrade kit.
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Re: Synth Defects - Ticking Time Bombs

Postby Hybrid88 » Mon Feb 23, 2015 7:44 am

Ensoniq Fizmo, the regulators in the power supply c**p out.

And the original tactile switches in the 303/606 and V-Synth don't last very long.
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Re: Synth Defects - Ticking Time Bombs

Postby coastalscrub » Mon Feb 23, 2015 8:36 am

Alex E wrote:The Roland JD-800 has the same keybed as the JV-80, D-70, U-20 and a couple others. If you can find a donor machine that hasn't had those weights fall out yet, you can swap the keys out. Cleaning that mess off the contact strips is another story.


Good to know. Do only the keys themselves from the JV-80/D-70/U-20 fit or the whole key assembly? The D-70 and U-20 have aftertouch but the JV-80 doesn't (or so says the web). I looked around and it looks like the D-70 and the U-20 also suffer from the red glue problem.
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Re: Synth Defects - Ticking Time Bombs

Postby Steve Jones » Mon Feb 23, 2015 8:59 am

Polysix power supply fails and the voltage goes high, killing IC's. Can also happen in the OBXa. Any synth that has a diode on the earth pin of a voltage regulator will go high voltage if that diode goes open circuit. I saw this happen to a Drumulator last year.

Juno 106 - Every juno 106 that I have serviced in the last couple of years has had circular cracks around the legs of the regulator and the two transistors mounted on the heat sink. If the earth pin on the regulator happens to lose it's connection due to the cracking the voltage will go high. Kurzweil K1000 modules can burn their molex connectors due to the amount of current that they carry.

Most Korg MS and PS series synths that I have serviced over the past few years have leaking electrolytics that can corrode the circuit board tracks. Every Roland CSQ sequencer that I have serviced has had severe battery leakage (the battery in these machines is inaccessible and invisible unless you strip the machine right down). I also see battery damage regularly in 909's, Yamaha CS-20's, Korg Poly 61's.

Any synth with a frayed or damaged power lead or damaged power switch is also risky and should be attended to immediately for obvious reasons.
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Re: Synth Defects - Ticking Time Bombs

Postby Alex E » Mon Feb 23, 2015 9:15 am

coastalscrub wrote:
Alex E wrote:The Roland JD-800 has the same keybed as the JV-80, D-70, U-20 and a couple others. If you can find a donor machine that hasn't had those weights fall out yet, you can swap the keys out. Cleaning that mess off the contact strips is another story.


Good to know. Do only the keys themselves from the JV-80/D-70/U-20 fit or the whole key assembly? The D-70 and U-20 have aftertouch but the JV-80 doesn't (or so says the web). I looked around and it looks like the D-70 and the U-20 also suffer from the red glue problem.


I know the keys are the same but I don't know about the entire keybed assembly per se. I think it might be possible if you use a U20. Someone should try it out.
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Re: Synth Defects - Ticking Time Bombs

Postby baz99 » Mon Feb 23, 2015 10:10 am

Korg synths from the M1 to the X5 family (and probably all models in between) are very prone to leaking capacitors.
This usually stays unnoticed until it's too late (when the acid has eaten up a few traces).
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Re: Synth Defects - Ticking Time Bombs

Postby mute » Mon Feb 23, 2015 10:26 am

Korg ESX-1 and EMX-1 have a fuse that often blows and and its in a chip so is hard to replace outside of doing a hack job with a soldered fuse or a bypass. FWIW ... I did a bypass and haven't had an issue since then (5 years).

Korg Poly-800 and Korg microX have shoddy terminals for the a/c adapter connection and often break/short/come loose.
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Re: Synth Defects - Ticking Time Bombs

Postby ppg_wavecomputer » Mon Feb 23, 2015 10:38 am

Mostly battery-related issues, e. g. with the Roland CR-78, PPG Wave, Prophet 5, or -- of course -- the Polysix. The early PPG Wave 2 have a dreadful Keyboard which is nearly impossible to fix with new bushings as it's no real Pratt and Read.

Power supplies tend to be prone to failure after some 30 years of use, causing chain reactions within the synthesiser. That's at least my experience. When working properly, they should cause no headache.

When looked after on a regular basis, a classic synthesiser shouldn't be too much of a hassle. In real life, though, many machines had been neglected for many years before they were unearthed or re-discovered hence you might potentially be in trouble.

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Re: Synth Defects - Ticking Time Bombs

Postby Percivale » Mon Feb 23, 2015 11:42 am

Kawai R-100. So much dust accumulates in connector pads that inputs would no longer register. A good clean/bath restored them to working order.
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Re: Synth Defects - Ticking Time Bombs

Postby Hybrid88 » Mon Feb 23, 2015 4:47 pm

ppg_wavecomputer wrote:The early PPG Wave 2 have a dreadful Keyboard which is nearly impossible to fix with new bushings as it's no real Pratt and Read...

Yeah I found that out the hard way on a 2.2, new bushings are just tight enough to make playing fast impossible. :(

Also got to mention the Yamaha DX-100 (and a lot of other 80's synths) that has it's jack board mounted without adequate strain relief causing cracks in the solder joints and intermittent input/output jacks. Annoying but a simple fix.
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Re: Synth Defects - Ticking Time Bombs

Postby ninja6485 » Mon Feb 23, 2015 5:10 pm

Every Roland product I have with buttons seems to have at least one that doesn't want to trigger - this varies from: you have to press it twice sometimes, to being extremely touchy and barely usable, to being completely unresponsive.
This looks like a psychotropic reaction. No wonder it's so popular...
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Re: Synth Defects - Ticking Time Bombs

Postby pflosi » Mon Feb 23, 2015 6:28 pm

So you just don't program rests in your 303? ;)

IME on the X0X machines the buttons tend to get better with regular use. Same for lots of Roland keyboards (the infamous double-triggering).
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Re: Synth Defects - Ticking Time Bombs

Postby Aaron2 » Mon Feb 23, 2015 6:39 pm

coastalscrub wrote:There are documented problems with a handful of synths where leaving the problem unaddressed causes major damage to the synth.

- Korg Polysix - the original NiCad battery leaks and causes catastrophic corrosion to circuit board.


The Korg Poly-61 has the same problem. Which is why at least 9 out of 10 that you'll encounter don't work! :x
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Re: Synth Defects - Ticking Time Bombs

Postby fh991586 » Mon Feb 23, 2015 6:53 pm

coastalscrub wrote:- Roland Juno 106 / MKS-70 / HS-60 - the voice chips have an epoxy coating that eventually short the chips resulting in dead voices.


The MKS-70 is fine on this subject: you got it mixed with the MKS-7 & MKS-30, which share the save epoxy chip as the Juno 106.
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