I have a Korg Mono/Poly MP-4. I was able to tune each Osc on Circuit
board KLM-398. However, as you ascend the keyboard up from the
lowest note to highest note, the pitch drifts up almost a 1/4 step or
so on all 4 oscs. This is even on all and the same. So, playing
octaves sounds a bit off. The manual says tune from the middle
octave, perhaps a "stretch" tuning is deliberate

Also, noticed after repeated playing of octaves that perhaps one out
of four repetitions will yield a pitch that is a bit off tune on just
one of the osc. There is no pattern here, it is random as to which
osc is out of tune and when.

Lastly, some times if you play two notes together in POLY mode, and
then quickly play a single note or let off the first note, you hear
the note you just let off sound when you play the next single note.
Like a double voice trigger. Changing release times and sustain
doesn't stop this behavior. Maybe it is the auto damp function
acting up

Any suggestions

TIA.