Need help on identifying amp defect Options

[soulsearchingsun]

I'm having issues with my mid-90s Sony solid state amp.
In particular the right channel is of lower volume (~-12dB in my measurements) and the sound is distorted in a way that there is noise added when I feed a signal to the amp. On silent parts, there is no additional noise. I ruled out the signal source and the speakers as the cause, it has to be the amp. I looked inside to see if I can find burned components, but I haven't had luck yet. I can't see the whole circuit board without disassembly (which I haven't done yet) though.

I uploaded a file here, with the following setup:
sound card output -> amp line level input; amp speaker out -> sound card line level input & speakers

Could anyone give me hints where I should look for the defect? Is this typical for some specific defect?
Thanks a lot!

edit:link now pointing to upload thread

This post has been edited by soulsearchingsun: Mar 1 2012, 14:32

[DVDdoug]

The waveforms don't look like a blown output transistor. It could be another transistor or IC, or maybe a capacitor that's throwing-off a bias voltage somewhere.

Of course it's always good to wiggle the wires & connectors around and push & pull the components around, because poor connections are the cause of many problems.

If you have an oscilloscope and a schematic, you should be able to trace-down the problem by comparing left & right channels at various stages/points.