Vintage Synth Repair

Replaced the diode but the problem remains. Even replaced ic7, ic8 and 
ic10, but nothing. It all leads to a faulty cpu chip. I didn�t want to 
go to the neighbourhood shop where they can scan the cpu activity since 
the guys there are not into synths, just tv repair work, but there�s 
nothing more I can do. Unless anyone here knows of more clues to 
diagnose the problem.

Paulo.