Korg M1 - one key not working

[tepr]

I have a Korg M1 that has been sitting in storage for a while. Got it out to test it, and found that one key was not working correctly - the top Bb.

Mostly it doesn't sound at all, but if I turn the velocity sensitivity all the way down to -10, I can get a note by pressing it hard.

Looking at the MIDI messages from the keyboard, it shows that a hard press on this key will generate a note with velocity of about 10; a normal press doesn't trigger it at all. For comparison, the other keys generate velocity around 60 with normal presses, as expected.

Sometimes - but not always - if another Bb is also pressed on the keyboard, then the faulty Bb will respond correctly. This makes me wonder if it's a problem with the scanning rather than the physical key.

Opening the keyboard up, everything looks fine. The key switches appear to be at the same height as all the other keys and move smoothly. Metering across the switch shows good continuity. The traces on the PCB attached to the keymech also show good continuity.

I had previously had a similar issue on a different key that turned out to be that the aftertouch sensor was dirty, and was resolved by cleaning it. No luck with that this time. I also disconnected the aftertouch sensor and found exactly the same behaviour - so I think we can rule out aftertouch as a potential cause.

Any suggestions please as to what I should try next? Thanks!

[Mooger5]

Never owned an M1, but I know it uses the same keyboard as the DX7. Maybe the following is of some help viewtopic.php?f=5&t=110938&p=815864#p815864

[tepr]

Thanks - yes that all makes sense. I'll take another look at the keyboard on my next day off and see if I have any luck with it.