Vintage Synth Repair

I suppose you have the service manual?

Check the main keyboard CV out (pin 8 on the connector). I believe this
should even work without the backplane. If this voltage changes after the
key release it's definitely a keyboard CV memory issue. Since you mention
that the pitch changes over time (not immediately) I believe that the
memory cap is actually working. Check Q7.

If all this fails I have a partly working MKI here that I could use to
compare measurements.