Yamaha M-65 Hum

patterncrab

New Member
A coworker recently gave me a pretty beat up M-65 with all of the speaker terminals broken off. After wiring the "A" output directly to the one remaining intact terminal block and capping off "B" and "C", I inserted the amp into a system. With the top cover off, I detected a squeal from the power supply area that sounds like 60 hz. There is no noise present at the speaker, and the squeal is constant and rather high-pitched. The amp sounds okay, but not like a Yamaha. The amp shows signs of having been run hot, but I cannot see any damaged circuitry. Does this sound familiar to anyone? I know just enough about electronics to get me into trouble, and would appreciate any input.
 
Look over the circuit boards for cracked solder or broken PC traces. Especially around the 4 large filter caps and the small rectifier board right behind the power transformer. If the amp has taken impacts that have broken the binding posts then, cracked solder and/or cracked circuit boards are also a possibility.
These amps have a know issue with glue contamination and corrosion around the two medium sized caps towards the front of the main amplifier board.

AK google "DSBG"
http://www.audiokarma.org/forums/showpost.php?p=3432894&postcount=1
 
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