I’ve got a SQ80 that has an issue with it’s (aftertouch) pressure. It seems to be always active for “all” keys. If I play very soft, full pressure is still being being sent from the entire keybed (LFO, etc.), not just one key. Also, after you try to play with hard pressure, it will lock up and try to recalibrate again after a few notes.
The coil boards look ok and pass multimeter and capacitance testing so far. Ribbon pins pass multimeter tests also. I’m wondering if this is a KPC issue. For now, I’ve disabled key pressure as a workaround of course.
As a side note, when I got the synth, it would fail calibration and gave the option to disable the keyboard. I found that pin1 (+5V) on the female side of keyboard connector on the KPC was corroded and broken off. I inserted a metal pin and soldered to get the connection backup. Pictures are attached. This allowed calibration to pass on boot up and the keys to start working again at least.