[sdiy] Repairability of modern analog synths

[Michael E Caloroso]

I brought a Memorymoog Plus back from the dead, complete restoration.
Everything was working, except autotune would fail about 30 seconds
after power up.

After confirming voices, autotune path, RAM, CTC, et al I was left
with one remaining component.  I swapped out the Z80 with a surplus I
had in stock... and that fixed the problem!

The one component I least expected to fail.  EVERYTHING ELSE WORKED!
I studied microprocessors in college, there must had been a bad
register on the Z80.

That was a witch hunt, but it proved the old adage of
troubleshooting... never rule ANYTHING out.  Even MICROPROCESSORS.

MC

On 10/20/20, Roman Sowa <modular at go2.pl> wrote:
> I've had one damaged microcontroller once. Can't remember the synth, but
> the damage was very tricky, and for some users could be even "I can live
> with that" type of fault. It was working, everything was fine, except
> pitchbend. I also thought "it's never the microcontroller" and searched
> for possible damage on the way. It quickly turned out that one
> microcontroller pin was used to detect the polarity of pitchbend wheel,
> and that pin was dead. You couldn't force it to the other state. Maybe
> some nasty ESD event from 30 years ago in the factory or simply bad
> luck. After micro replacement it worked as new.
>
> And that's not yet the strangest fault I've seen in a synth.
>
> Roman
>
> W dniu 2020-10-20 o 15:03, Gordonjcp pisze:
>> On Mon, Oct 19, 2020 at 03:42:34PM -0700, David G Dixon wrote:
>>> It would seem to me that one big problem with "modern" synths is
>>> replacing
>>> programmed chips.  I can't speak for other people, but when I open up a
>>> broken synth and see microcontrollers, I close it back up and leave it
>>> where
>>> I found it.
>>
>> Why?  It's never the microcontroller.
>>
>> That's like all the crappy garages that used to go "oooooh, can't fix
>> that, it's got a computer, it'll be the computer that's faulty, that's
>> expensive and needs dealer tools".  Does it hell, it needs a set of tyres
>> put on, you lazy tit.
>>
>> If you see a modernish synth with a fault, it's going to be the power
>> supply or one of the much-maligned 405x MUXes.  The closest I've got to a
>> faulty microcontroller in a synth is doing the DSP in MS2000s - funny I've
>> never seen a Microkorg with a dead DSP!
>>
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