Korg Polysix Sub ocs stuck

My Korg Polysix’s sub oscillator is constantly on (2 octaves below too) and the switch or changing presets does not change this. Any ideas how to fix this or where to look for a solution? Thanks!

Always the first question with a Polysix: Is there a acid leakage from the battery?
The controlling IC (IC29 CD4024) is located in the leakage endangered area.

Does the switch for the modulation selection VCO / VCF / VCA work correctly? The VCO and VCA settings come from the same chip.

In very grey theory also the panel scanning could cause such a problem, but it is not that likely.

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Thank you fanwander for your quick response. There was some leakage from the previous owner that was cleaned up, mainly affecting ic31 that has been replaced. The modulation works as it should too. Would leakage be able to cause damage to the scanning? (I’m not very electronics savvy, having a friend come over to test the different parts soon)

sorry for the late answer: if there was leakage, then I recommend to check the bus lines from ICs 30 and 31 to the right side direction 26 and 28 29. Even if the ICs are ok and the traces look good: the so called via’s (copper plated holes, that connect a line on one side of the pcb with a line on the other side if the pcb) can loose their copper due to corrosion.

About the influence of a acid leakage to the panel scanning: yes and no. The Suboscillator is scanned via the line D01 which is derived from IC31 pin11, but also the selection modulation VCO / VCF / VCA is scanned via this line. So if assigning the modulation to all three destinations works, then it is very unlikely that the panel scanning is affected.

My first attempt would be now: replace IC29