Vintage Synth Repair

My Kawai K3 stopped producing sound and the LED display on the front 
stopped displaying anything.  I have checked the power supply (+-12v 
and +5v) and they are fine.  Chuck Roberts at Kawai says that it 
appears to be a logic error that is shutting it down.  I removed the 
main synth board under the keypad and then the LED display partially 
works, but still no sounds.

Does anyone have any guesses as to what might be wrong?  Could the 
membrame keypad above the 'motherboard' have some corrosion which is 
shorting, because disturbing the 'motherboard' caused the display to 
partially work?


thanks.  Brian.