hifi engine

Yamaha M2

madisonhack's picture

I'm working on a Yamaha M2 amp and have a problem that is causing me fits. After replacing missing output transistors and performing a check for bias and idle current, I discover that I have distortion in the left channel. I've traced the problem to the pre-driver board of the left channel. Does anybody know this unit well enough to comment on the specifics of this board? I'm seeing audio on the regulator side of the series resistor that feeds the -80 volt rail, unlike either the +80 volt regulator which is identical or the working pre-driver board of the right channel. My guess is that I either have a component that is drawing excessive current on that rail (transistor/capacitor) or I have a decoupling problem again in a defective capacitor. I've changed enough components that I now know that I'm spinning my wheels. Thanks.