Sony STR-313L receiver repair - broken channel

[Zephyr]

I bought a Sony STR-313L off ebay recently but it arrived with the right channel bust: the output at the speakers reads 9V DC, compared to a 55mV offset on the left channel. I've traced the problem using the schematics and a trusty voltmeter to find that the two pins corresponding to right-out on the power amp chip have 9V on them, while the left-outs are the normal 55mV. There seems to be nothing wrong with the circuits up to that point, and the 9V right-channel persists all the way from the power amp chip outputs, through the tone adjust, to the speaker/headphone out.

What I need to know is if this means the chip is at fault, before I rush off to get a new one. I've attached links to the schematics (sorry they're so big), with the relevant bits marked, in case someone's willing to have a look. The dodgy pins reading 9V rather than 0V on the power amp chip are nos. 10 and 12. The chip is an SI1125HD, if that helps.

More information, in case it's relevant: when I flick the amp's off switch, there's about half a second when normal, fading sound comes out of the right channel, just as it does from the left. And during normal operation, if I turn the volume up VERY high, I can hear the right channel softly, behind a hissing noise. At normal volume levels, it just makes a hissing noise. The left works perfectly normally.

It's a beautiful machine, and I'd like to fix it. Does anyone have any experience of something like this?

Diagrams:
PCB diagram
Schematic
And the thing itself (not mine, but it's the same):

 

[TheAudiotech]

Bad IC

Hi! It sounds like you found the problem, you are getting DC to the speaker from the IC, I would isolate pin 12 first and see what you get on the pin (probably your 9V), if not do the same with pin 10. Normally you would expect the rail voltage at the audio output pin when the amp IC fails. You're gonna have to do some digging to find that IC, it has been extinct for for some time now.

Steve

 

[dr*audio]

See those 100uF caps tro ground on pin 3? I'd check that first on the bad channel, just to be sure. You're supposed to get -32V or so on that pin. If it's more positive, I'd replace the cap. then if the cap doesn't fix it, you've got an IC to replace.