Discussion about the Korg PolySix synthesizer

To add to what Bob has been saying:

The attenuator does not affects KLM366 (the voice board), it affects KLM368
(the effects board). The signal is called "P.VOL" (probably for
"Programmable Volume" in the schematic, and we can see that it travels on
CN03-6. That's the second pin from the bottom for the orange cable.

Now, you mentioned that you're using a clone now and that the old board had
acid damage. I've found it more than once that this damage had spread to
the KLM368 which is directly next to it; and especially to the area where
the connector between KLM367 and KLM368 is located. Remove KLM368 and check
the bottom of it for damage.