Discussion about the Korg PolySix synthesizer

PolySix Key Tracking / Filter voice issue

KLM366 v1 with daughterboard.

The key tracking voltage is fed into IC23 on the 366, and output for each voice.

As the key tracking is raised, one output voltage doesn’t follow the others. It gets pulled lower the higher the voltage input so the drop in pitch is very noticeable at a high self-oscillation setting.

I replaced IC 23 and 24 and checked the subsequent resistors and caps and the 4558 but no change.

Any ideas ?