[sdiy] Korg M500 keyboard problem

[Louis van Dompselaar]

I have a Korg M500 under repair that is impossible to tune.  I can't get
the C much lower than a flat F.  Also, the lower octave can't be tuned
narrower than 13 semitones and the upper is almost 18 semitones.

It's probably all due to the keyboard.  It is (very) similar to the MS10/20,
but the output voltages are odd.  Upper C is 10V, middle C is 4V and
lower C is 1.88V.  I don't think I can ever get that tuned.  Anyone ever
seen that on a Korg V/Hz keyboard?