Vintage Synth Repair

Hi!!!

Not sure if Korg O1Wfd is vintage yet, but here goes: My trusty O1Wfd has developed an irritating error and I would very much like to
know where to start to look for the source of the problem.

It goes like this: You play a chord and there will be other notes sounding in
addition to those you have played. They play at random time (but always 1-2
sec. after you have pressed the keys for the chord you want) and they often are
one or two of the notes you used in previous chord you played. They also are
louder and slightly distorted in sound. There´s also high pitched crackle in the
background, while the "ghost notes" appear...

They seem to have something to do with longer release times and reverbs, because
they hardly ever appear with short sounds with zero attack and zero release,
like "mono lead" etc. Short polyphonic sounds are OK as well, so it´s probably
not about mono/poly mode...

Combi and Prog sounds are most badly affected, but when played via Seq mode
there are much less problems. The shorter sounds are mostly faultless in seq
mode.

I would imagine that someone else has also come accross this kind of
malfunction, so I would be very thankful for any pointers for the problem
source.

I downloaded all data from the factory disk, performed the data dump from
another O1 and tried to play the faulty O1Wfd via midi from other keyboard, but
the problem was always there...

thanks in advance for any recommendations,

cheers,
Ami