Synth Defects - Ticking Time Bombs

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Re: Synth Defects - Ticking Time Bombs

Postby ppg_wavecomputer » Tue Feb 24, 2015 2:28 pm

mmp wrote: [...] Road case foam rot ruins exterior finish.


That's true for every type of softer grey foam that is used to line cases with -- curiously, the type of foam made from recycled flakes seems to hold up better.

Rule of thumb: Check/replace foam lining after some ten years.

In most cases (no pun), residue can be removed using lighter fuel or rubbing alcohol, especially when the surface has been lacquered or oiled (wooden enclosures). With metal enclosures (Jupiter 8 et al.) this becomes more of an issue as the foam can eat into the silkscreened lettering etc.

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Re: Synth Defects - Ticking Time Bombs

Postby adamstan » Tue Feb 24, 2015 2:50 pm

Siel Opera 6/DK600/Kiwi is another one, which suffers from NiCad battery damage.
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Re: Synth Defects - Ticking Time Bombs

Postby ninja6485 » Tue Feb 24, 2015 5:41 pm

pflosi wrote: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).
You know, it's never come up ;) :lol: But yea, I've noticed they do on the xoxs for the most part. My D50 and mc500 are the worst offenders. I still don't know what sounds are in Bank 7 on the D! Thank god 8t integrates so well with its pc editor!
This looks like a psychotropic reaction. No wonder it's so popular...
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Re: Synth Defects - Ticking Time Bombs

Postby grenert » Tue Feb 24, 2015 6:30 pm

The Siel Expander also dies a similar, leaky-battery death as the Opera 6/DK600 mentioned above.

Many synths with PCB-mounted 1/4" jacks that are not secured to the case can develop problems over time as the cables get torqued and jack housings crack and fall apart.

Later Pro-Ones with the membrane keyboard eventually become intermittent and require cleaning of the internal membrane connections (not easy).
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Re: Synth Defects - Ticking Time Bombs

Postby sam » Tue Feb 24, 2015 10:06 pm

The opto coupler which controls the tuning in the polysix are slowly becoming a problem..if any one has a fix for this I am very interested to know..
Chorus chips in the 106 are also going down...
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Re: Synth Defects - Ticking Time Bombs

Postby EmptySet » Wed Feb 25, 2015 6:34 am

I've seen a number of JX3P control panel switches go south. Or you have to press them five times to get them to work. Worse yet, there is NO replacement available for them. You can rip apart another 3P for parts but that's it. Really a bummer, especially since it looks promising as they're ALPS switches.

Others have mentioned it, but man, that MOOG goo in Opus et al synths has got to be the worst thing I've seen happen to a synth. There really is no description suitable for how horrid the mess is.

I've also replaced quite a few caps in DX7s power supplies. Otherwise that synth seems really solid.
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Re: Synth Defects - Ticking Time Bombs

Postby ItsMeOnly » Wed Feb 25, 2015 11:52 pm

Korg 01W: leaking caps. Judging by the forum and blog posts, the C95 and C96 and also C100 and C101 capacitors were basically timed spark-plugs that bombed the instrument after almost fixed period of time (usually ~7 years).
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Re: Synth Defects - Ticking Time Bombs

Postby Re-Member » Thu Feb 26, 2015 1:33 am

My SH-101 suffered an instant K.O. when I accidentally plugged in the wrong power supply. I took it to a repair shop that specialized in vintage synths and the guy said it was a pretty common problem with the 101 and easy to fix. I only had to pay the one-hour charge minimum and nothing more. Since then, I'd had the power supply cord wrapped in bright red tape to avoid it ever happening again. The moral of the story is never try to reorganize your gear while drunk. :roll:
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Re: Synth Defects - Ticking Time Bombs

Postby sneakthief » Thu Feb 26, 2015 6:56 am

1. SH-101
Speaking of the SH-101, the power button has 2 poles: one to send power to the regulator and one to send the regulated voltage to the DAC.

Unfortunately as time goes by, the switch corrodes/oxidizes and the varying resistance makes the DAC freak out and therefore causes the wobbliest pitch at the slightest touch.

The fix I use is simply to jumper that side of the switch and install a relay instead - which is turned on and off by the first side of the switch.

2. Yamaha RS7000

Here's a problem that I've never seen documented but have had in both my RS7000's and one other guy's:

The switching PSU has a chunky transformer in it. If you tour with your RS7000, there's a good chance that the solder joints below it will crack, leading to intermittent power, especially when first turning it on.

The quick fix is to use tons of solder on those joints. Maybe epoxy glue would also help.
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Re: Synth Defects - Ticking Time Bombs

Postby HideawayStudio » Thu Feb 26, 2015 9:51 am

rschnier wrote:ARP Omni / Omni-2. Power supply throws voltage spikes when powered up, causing damage over time to the many tantalum (decoupling) capacitors connected across the power supply rails throughout the synth, eventually causing one or more to dead-short. Since the power supply rails are not fused, when the dead short happens it takes the power supply and other components down with it.


In truth it often amazes me how reliable most music gear is but with most vintage synths now being 25+ years old frankly there is a potential ticking time bomb in every one of them - after all, how long would you expect the other electronic gear in your house/studio to operate without fault?

There seems to be a little bit of hysteria over the Omni PSU which frankly is no worse than most other inexpensive linear series-transistor designs. The LM723 regulator is well understood in external series transistor applications and still in production to this day and has been used in countless designs over many decades. This regulator offers external current sensing and limiting and is implemented in this fashion in the Omni using sense resistors. Transistor substitution is not an issue either as the design is not critical owing to its closed loop design and even the transient suppressors suggested by ARP are still in production:

http://uk.mouser.com/ProductDetail/Litt ... JQUA%3D%3D

I am not saying this is a great PSU but it isn't as terrible as some make out.

I actually suspect there were some politics in play here and the issues have been clouded with time. The 35+ year old tantalum capacitors ARP were using were known even back then as being extremely poor quality and I very much doubt most would have survived any longer running on any PSU design (the steep rapid climb to normal rail voltage on every power up even without overshoot will eventually kill bad tants anyway). This is why I'm concerned people who have retrofitted their Omnis with "medical grade" retrofit PSUs may be lulled into a false sense of security if they haven't recapped their instruments first.

What is often overlooked is that the vast majority of tants in the Omni are not even used in the usual PSU decoupling roles but in fact are used to implement the timing aspects of the keying circuits ie. the very worst place you could put a low ESR device as they will be subject to literally hundreds of thousands of voltage transitions during their lives by the very nature of the circuits.

Why you ask... for another reason that is often overlooked - although these days we usually only use tants for their low ESR properties in those days tants were seen as offering the best packing density and were very often therefore used in tightly packed circuits and not necessarily for their electronic properties. This is why their replacement with modern miniature electrolytics is often perfectly acceptable.

I work on a lot of gear from this era and I'm seeing the same/similar capacitors failing randomly in a plethora of instruments. In fact in the early 80's E-mu were sufficiently brave to raise an ECN to the effect of "do no use ITT tantalum capacitors in new designs!" - the very same caps that had failed in the Crumar GDS.

The second issue of failing CMOS chips in the Omni is due to a couple of issues (and certainly PSU transients won't help) but in the main frankly these are going to fail with extreme age regardless of PSU design as the early CMOS multiplexors are absolutely notorious for going leaky in all manner of ways or just failing outright. Replacing these with modern parts makes a lot of sense as their susceptibility to transients became understood and were later ironed out to a certain degree and frankly there isn't a vintage synth with CMOS MUX from this era on the planet that isn't immune to this growing issue.

I'm working on yet another very poorly DK Synergy this week and guess what had melted the linear PSU rail transformer?... yup, you guessed it - yet another dead short tantalum capacitor.. and no, the PSU design is distributed with local regulators and entirely different to the Omni.
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Re: Synth Defects - Ticking Time Bombs

Postby rschnier » Thu Feb 26, 2015 7:01 pm

HideawayStudio wrote:There seems to be a little bit of hysteria over the Omni PSU which frankly is no worse than most other inexpensive linear series-transistor designs.

Hm, not meaning to convey "hysteria" :? However...

I guess I see the issues with the Omni/2 as being a convergence of two (actually three, if you count the decision to not put fuses at the power supply outputs) design decisions that when combined, created an outcome much worse than either would have otherwise caused alone. Normally it's a good decision to use tants to decouple the rails on digital circults, as they have the lowest self-inductance of available capacitor technologies (and of course, lower self-inductance means better ability to decouple out the high-frequency hash on the PS rails). But ARP put tons of those little buggers across a power supply that has since proved to be prone to overvoltage conditions -- the one thing that's most deadly to a tantalum capacitor. If ARP had used electrolytics and mylar caps for decoupling, for example, OR if they'd used a power supply design that wasn't as apparently prone to overvoltage (just to save the cost of a dedicated regulator for the negative rail?) -- or even just put a couple fuses at the output of the power supply :( -- there wouldn't be as many catastrophically-dead (i.e. cascading toastage) Omni's out there. (I own two; both were acquired after they fried on their previous owners. I know you have at least one also, Dan, so am not disagreeing with your points.)

Sure, we'd still be seeing some failures, as tantalums will still occasionally fail, as you mentioned Dan. But what happens in an Omni when things go boom is what (to me) puts it in a different class of vigilance required (and thus worthy of mention in this thread), in the same way as Korg's decision to put a leak-prone battery right in the middle of the Polysix's main CPU board puts that at another level of vigilance. If someone can possibly manage to catch it before it happens and prevent the "boom," they save themselves much more heartache and tears than in your typical garden-variety failure where you just need to have the failing part replaced and then you're good again. I'm not disagreeing with you, not at all -- I just hate to see wonderful, vintage electronics burn itself up. I guess the moral may be...in all these vintage synths, take extra-good care of their power supplies and what's across the PS distribution rails....
Last edited by rschnier on Thu Feb 26, 2015 9:57 pm, edited 6 times in total.
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Re: Synth Defects - Ticking Time Bombs

Postby madtheory » Thu Feb 26, 2015 7:10 pm

Brilliant analysis Dan. The synth community is lucky to have someone with your expertise, love of the instruments and and the willingness to share!
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Re: Synth Defects - Ticking Time Bombs

Postby princefan3 » Thu Feb 26, 2015 8:06 pm

Dam....I own both a Mk 1 Omni and a Korg Poly 61 which actually works.

The Omni I don't have to worry about as in Tech world as we speak...New power supply and Tants all over.

Korg Poly though I am worried about...opened the lid and squinted at the battery area....

No damage so far but looks like the old light blue baby in there...it looks in top nick though not like an old battery, but this might be misleading me...would it be safe to place some type of foil or plastic cover underneath the battery just in case it went..

Not sure if I should just get rid and forget i ever had one.
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Re: Synth Defects - Ticking Time Bombs

Postby rschnier » Thu Feb 26, 2015 9:13 pm

princefan3 wrote:would it be safe to place some type of foil or plastic cover underneath the battery just in case it went..

Often it's not just leakage onto the circuit board that causes damage; these batteries also tend to emit a corrosive vapor at the same time they leak, damaging board traces and other components within a several-cm radius. So, not sure whether putting foil or plastic under just the battery would provide enough protection to justify the effort. If you can manage to, it's best to replace if over 5 years old, and then keep it replaced every 4-5 years (?) as time goes on.

The Polysix's battery type seemed to be among the worst for emitting the vapor, as luck would have it.
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Re: Synth Defects - Ticking Time Bombs

Postby HideawayStudio » Thu Feb 26, 2015 9:54 pm

rschnier wrote:Hm, not meaning to convey "hysteria" :? However...

I guess I see the issues with the Omni/2 as being a convergence of two (actually three, if you count the decision to not put fuses at the power supply outputs) design decisions that when combined, created an outcome much worse than either would have otherwise caused alone. Normally it's a good decision to use tants to decouple the rails on digital circults, as they have the lowest self-inductance of available capacitor technologies (and of course, lower self-inductance means better ability to decouple out the high-frequency hash on the PS rails). But ARP combined that with a power supply that was prone to overvoltage conditions -- the one thing that's most deadly to a tantalum capacitor. If ARP had used electrolytics and mylar caps for decoupling, for example, OR if they'd used a power supply design that wasn't as apparently prone to overvoltage -- or even just put a couple fuses at the output of the power supply :( -- there wouldn't be as many catastrophically-dead (i.e. cascading toastage) Omni's out there. (I own two; both were acquired after they fried on their previous owners.)

Sure, we'd still be seeing some failures, as tantalums will still occasionally fail, as you mentioned Dan. But what happens in an Omni when things go boom is what (to me) puts it in a different class of vigilance required (and thus worthy of mention in this thread), in the same way as Korg's decision to put a leak-prone battery right in the middle of the Polysix's main CPU board puts that at another level of vigilance. If someone can possibly manage to catch it before it happens and prevent the "boom," they save themselves much more heartache and tears than in your typical garden-variety failure where you just need to have the failing part replaced and then you're good again. I'm not disagreeing with you, not at all -- I just hate to see wonderful, vintage electronics burn itself up. I guess the moral may be...in all these vintage synths, take extra-good care of their power supplies and what's across the PS distribution rails....


I honestly think this is not so much a design issue but actually a pretty decent design ruined by poor quality parts. The PSU is current limited so ARP did their due diligence. What I doubt they expected though was to witness a sea of premature tantalum cap failures. ARP were notorious for their designs suffering due to the bean counters having their way - their products suffered endless quality issues due to poor quality parts such as cheap sliders, trim pots, caps and connectors.

On paper the capacitors in the Omni are very conservatively rated with the lowest voltage rating tantalum cap still spec'd at 10 volts above the 15 volt supply rail - most on the supply rails are rated way beyond it at 35 volts which in theory shouldn't fail even if the series transistors in the PSU go dead short let alone suffer an overshoot condition on power up - by this point half the synths CMOS would have been blown away anyway (which sadly happens from time to time with Omnis!)

In this day and age you are lucky see a 20% safety factor on tantalum voltage ratings with many parts on 5 volt rails rated at 6.3 volts.
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