Discussion about the Korg PolySix synthesizer

VCA Mod is the LFO signal if the switch in the LFO section is in the VCA
position.

You might also want to check the cable itself. Sometimes the battery acid
has affected the cable or the connectors. While I have seen this most
commonly with the Poly 61 I have also seen at least one case where the acid
had move partially inside the cable isolation.