[sdiy] Korg Minikorg 700S issue

[Mike Bryant]

Sounds like the sample and hold is loosing charge on the capacitor.  Look for a high quality capacitor - probably something in the range 2.2nF to 47nF with an opamp nearby - fed from the keyboard and first clean the PCB spotlessly around it, and if that doesn't work change it.
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From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Luís Marka via Synth-diy <synth-diy at synth-diy.org>
Sent: 21 December 2024 13:50
To: synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: [sdiy] Korg Minikorg 700S issue


Hey gang!

I am finishing a restoration on my good old Korg Minikorg 700S. I got it some 30 years ago and in fact, I think some of the front panel switches never worked properly before... now that I opened and cleaned every switch and slider, it indeed works so much better. However, two issues still remain: one, engaging the "Bender" switch takes it ou of tune: pressed keys never reach their intended frequencies; not sure if this is by design or not. Actually, holding a note and engaging Bender takes its frequency down. And two, releasing a key when Sustain (in fact, Release) is turned on makes the pitch slooowly slide down, almost like a pitch bend being applied to the note. Holding a key maintains the pitch, but soon as it is released, the pitch decays.


I already checked all resistors and replaced every capacitor around the Keio VCO module, but it made no difference. Has anyone ran into such issues before?


Thanks!
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