Hi, I’m curious about the typical causes of component failure. Having my old 1970’s Pioneer receiver recapped and running again has made me wonder about the sorts of issues my aging synths will be facing and any kind of care of maintenance needed to keep them happy making their crazy sounds for years to come? My understanding is that capacitors are like batteries in that they eventually go bad and need to be replaced. Do you wait for them to fail, or recap them ahead of time? What other parts are prone to fail that I need to be aware of?
Hey, this is a great question. If you are resurrecting a synth that has been tucked away unused for 20 or 30 years (which we often do), here are the main things we do, in order of importance:
BATTERY: If the synth uses a coin-type Lithium battery, it may be dead, but that’s no big deal. The terrible thing to find is a synth that uses a rechargeable battery (typically a NiCad) which has sat for so long that it has leaked corrosive material. This can often be seen as bluish-white crystal growth around the battery terminals - like on car battery terminals that needs attention. This can have devastating results on a synthesizer. Once you clean that stuff off, and remove the battery, you may find that the circuit board traces have turned black in places, and may no longer be conducting electricity over those bad spots. There may be many traces that need to be repaired, and that is a very tedious process. Components that such a trace connects to, such as ICs, may be damaged as well, and need to be replaced. I have even seen instances where this corrosion has travelled through a wiring harness, and affected an adjacent circuit board.
The Korg Polysix and Poly-61 are good examples of this situation. If you are looking at one of these and it powers up but behaves very strangely, you are probably experiencing battery corrosion in action. Generalmusic also made keyboards that use a large NiCad battery.
If the synth uses D-cell or similar batteries to actually power it up (Korg Poly-800, for example), these may have leaked if left unused for years. That’s a mess too, but not nearly as damaging as the above description, because for one thing, they are typically in their own housing, removed from the circuit boards.
Just an aside: The batteries in most synths have NOTHING to do with their operation. Their only function is to retain program and/or sequencer data when the keyboard is powered off. Many people trying to bring a dead synth back to life think, first thing, ‘Maybe it’s the battery…’ It’s not. You can remove the battery, and the synth should still operate normally. (This doesn’t apply, of course, if the battery actually powers the synth, as in the above Poly-800 example - though the Poly-800 can also work with a power adapter. And another exception is the Yamaha DX7, which loses all programs when the battery dies, and then makes no sound. As with other synths, you can still program a sound from scratch and it will operate normally - but that’s not so easy on a DX7…)
TANTALUM CAPACITORS: Tantalum caps are teardrop-shaped capacitors, often in a cheery red or blue color. The problem with tantalum caps is that when they die, they short out. Most other components simply stop passing electricity when they die - which is much safer. If you stop passing electricity, the unit simply stops working. But if you short out, nasty things can happen, often resulting in smoke and frying components. So on an old synth, we go through the power supply and replace any tantalum caps with electrolytic caps. (Note that both tantalums and electrolytics are polarized - they will have one + and one - lead, and have to be oriented correctly. And they also have a voltage rating, so whatever cap you use one has to have the same voltage rating or higher than the one you are replacing.)
We do this routinely on the power supply, because a short here can have terrible consequences on everything hooked up to the power supply (i.e. the voice circuitry, etc.). We typically do not replace tantalums beyond the power supply (unless they are actually dead), because (a) they may be involved in the character of the sound, and (b) the consequences if one shorts out are much less devastating. And there could be dozens of them, so a total recapping can be a huge and unnecessary project.
ELECTROLYTIC CAPS: As these age, they do degrade, and so we will often replace these on a power supply board - again, trouble on the power supply can cause delicate components to fail, so this is often a good preventive maintenance chore. Sometimes you can see the caps actually bulging - that’s a bad sign. Sometimes, though, the larger caps have a glue that supports them on the PCB - so don’t see that hardened ‘puddle’, and think that the cap is leaking. We kind of play it by ear on recapping these, depending on the age of the unit. Some techs recap routinely, others have a ‘If it ain’t broke, don’t fix it’ view.
And like with tantalums, beyond the power supply, we don’t replace electrolytics unless they aren’t working. On many units, the caps play a significant role in the sound, so if it’s sounding good, leave it alone.
OTHER: Other than those things, which apply generally, some synths have specific things that are their ‘Achilles heel’. Roland Juno-106 voice chips, Ensoniq Fizmo voltage regulator, Alesis Ion output transistors - these things are well documented causes of many failures. A quick Google search of a keyboard you are working on will bring up these sorts of things.
Again, excellent topic - I hope this helps!
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Also have a look at CMOS substrate failure
today fabrication and yields, move to newer technologies NMOS etc mean that CMOS substrate failure is less of an issue.
Some chips have very low production runs (in the low 000s) and so have a higher rate of failure eg. PD508 / CEM 5508
Heat is always a factor, even a small DC fan drawing away hot air will increase longevity.
NASA have great papers on this stuff.