Hi Alan

> From your description it sounds like you filter chip SSM2044 may have
> gone.

first he should check whether there is a signal at pin 1 (input) of the
SSM2044
Also it is worth checking the four ICs 2033 at pin 8, 3 and 12 whether
there is a signal.

> mean it seems that the rubber contact has corroded or the PCB contact
> You night find the rubber strips on ebay. same type as in the polysix
> and another few keyboards. as for finding a complete keyboard PCB that
> might be more tricky.

check also http://www.oldcrows.net/~oldcrow/synth/korg/polysix/keyclean.html

If the contacts don't work ever, then maybe also some of the diodes in
the keyboard matrix might have died.

Florian