Discussion about the Korg PolySix synthesizer

Do you have the service manual handy?

I'd probably put the Polysix in Unison mode, oscillator at sawtooth, no
subosc - and then play a note.

The filter input is at pin1 of the SSM2044; the signal there is pretty weak
- about 40mV or so. But in theory you should see a clear sawtooth there.

If you have a signal there you should check if it makes it through the
filter. Put Cutoff at max and all other filter setting to zero (which means
for EG Intensity center).
In theory you should now see a similar sawtooth at pin3 of the 2044. If not
then this hints at some problem within the filter. You could easily find
out if the filter IC is faulty by swapping it with one from a working
channel then.

For the envelope you might want to put all controls in the middle; then
measure the top side of R143 for each channel. In theory you should see the
voltage change from the envelope there (between 0 and about 5 volts).

Anyway, this should get you started, I hope.