Archive of the former Yahoo!Groups mailing list: Discussion about the Korg PolySix synthesizer

If you look at the schematic for the KLM-370 front panel pcb, you can see that the filter
controls and the ADSR controls are in the same 4051 analog mux. The A,B and C select
inputs select one of the 8 analog values to be measured by the CPU board. If the C line is stuck
high, or possibly floating high, then the CPU will always select the D, S, and R pots along with the
keytrack one. It would select those pots even when it thinks it is measuring the filter cutoff and resonance
ones. So maybe check that signal to see if it's connected all the way from the KLM-370 front panel board
through the KLM-369 board, and back to the CPU board with a DMM in resistance mode.
(synth powered down, of course) If you have a scope, just check the signal at the 4051 mux on the KLM-370
to see that it is switching.