Magaling,
I have repaired two KN2000 keyboards, my own and a friends. Both problems were related to the power supplies. Not the same problems as yours, but it seems that the power supplies are trouble makers and the keyboard is sensitive to power supply voltage levels.
The problem with service is being able to find the all of the places to measure the various voltages, of which there are many.
Do you have the schematics and the PC board layouts?
I might be able to send the files to you if necessary.
Walt