Sony STR-AV19 Left Channel weak when quiet?

[macjedimatt]

I have a Sony STR-AV19 that works great when the music is on the loud side. But if things get quiet, I start to loose the left channel. It gets quiet and a little fuzzy sounding. It does the same thing no matter what the physical position of the volume knob is. It also seems to get worse if I have it running for a couple hours. I've had it taken apart and I don't see any visible damage. The service manual is available here: http://sportsbil.com/sony/STR/STR-A/STR-AV19.pdf

Does anyone have any ideas where I should start looking? The volume knob sounds clean, so I don't think it's the potentiometer.

-Thanks

[CapLeaker]

compare the left channel to the right channel when its acting up. look with an oscilloscope on which stages of amplification things are normal or not. look also for bad solder joints and make sure that all voltage rails are good.

[jons]

Check output relay - if their contacts oxidize enough to make some resistance between them then amp can act like this.

[R_J]

Try pushing the speaker switch a few times to clean the contacts to see if that helps, if not then a scope would be needed to trace and compare the audio signal.
Try the tone and balance controls as well to see if they have any effect on the low audio.

[macjedimatt]

I finally figured out what the issue was. The speaker protection relay has bad contacts. I've by-passed it for now and will eventually order a new one to replace it since cleaning the contacts didn't help at all.