I doubt very much Don Scott is interested in trouble shooting and repairs. Mike Zucarro I mentioned is in with the same "tunerinfo" crowd as Don Scott. You could also try the Tunerinfo filter expert Bob Fitzgerald who can also fine tune it better than new. Bob is at bfitzge2@nycap.rr.com
If this is just an electronics repair, then your local/nearest authorized Yamaha technician can probably get his hands on the service manual and fix it.