Great to be able to help.
You can close your topic finally!

It's almost 25 years ago I had an MS20 so the knowledge is a bit rusty. As far as I know the MS20 KBD sends out 2 signals only (check the patch panel): - CV - Trig However, and this you need to check, what was called 'Trig' on the MS20 I believe is actually a Gate. Check it out please: what happens ...

Assuming the keybed is made similar to other keybeds, you might experience a bad contact on that key.
Might requiring cleaning.

Can you still create a patch?
If not, could it be all your presets are messed up? If that is the case, you may have to replace the back up battery inside and then reload via MIDI Sysex the factory presets.

Hi, I used to have an SX240 myself, so I get what you mean. If only one of the eight voices is no longer functioning, then probably a hardware problem. To figure out what is wrong, you will have to peek inside. I have never opened it up myself, so there I can't help you. But look for an area where y...