Discussion about the Korg PolySix synthesizer

Hello,
I've just repaired my second polysix and third KLM-367 and I thought
I'd share my latest findings. I did the usual IC replacements,
including the 40 pin IC socket and a lot of board cleanup with alcohol
but I've noticed that it seems tricky to make the surface of the board
totally non-conductive after the battery has leaked and soaked in. 
This seems to show itself as really strange crosstalk between traces.
The digital side of things seems to cope with this but one thing had
been bugging me.

I could never get a totally steady note, there was always a bit of
glitchy FM creeping in. I isolated it to the VCO Mod mixer IC8, but
couldn't see how it was getting there. In the end I lifted R9, put in
a new local C43 and used hook-up wire to get to the control panel
connector. No more wobbly oscillators!
The bad FM must've been coming from digital signals getting mixed into
the trace that ran under the former home of the battery, past the
4011s and eventually to the other edge of the board. This track is
relatively hi-z, so it's vulnerable to that kind of thing.

Now I know why Old Crow removes the suspect traces entirely, once the
battery has leaked you can't rely on them to do anything they were
designed to do *even if they test for continuity properly*

--
philb