Onkyo TX-SR501 riddle - no sound but it works in every other sense...

[alexdanis]

Hello everyone,

I recently became the owner of this Onkyo amplifier (for free by a friend moving out, cool right?). The amp is a home theater model, but I would like to use it as a stereo amp. Problem is as follows:
Plug the amplifier and turn it on. Everything looks ok, the screen is on, you can change the settings, choose a different source, adjust volume etc.. But when you connect a pair of speakers, in any of the two channels (A+B) for stereo there is no sound coming out of the speakers. The speakers themselves are ok, I have tried them with a different amp and the work flawlessly.

In order to locate the problem, feed the amp with a signal on the CD input and use the tape out exits to lead the signal to another amp that I own that works. With this setup there is sound, so I assumed that the pre-amp module of the amp works. I then opened the amp and thought, why not remove the fuses and check them thoroughly? I did and they were ok. After that I connected again a pair of speakers and oh! a miracle there was sound coming out of the Onkyo (actually sounds a lot better than my other amp too...). I tried all possible inputs and each one was working, volume control was working, bass/treble adjustments, everything. But after about 5 minutes it made a weird noise like somebody pulled the plug and then no sound again.

Volume control and input selection etc (pre-amp module) was again responsive. But but nothing coming out of any of the speaker connectors. If I power it off, unplug it and plug it again it plays for about a minute and then stops. The sound it makes before stopping is not like a scratching sound that would lead me to look for loosened wires, but something more abrupt. Puf and no sound sort of. The fact that it still functional makes me think that is not related to the power supply circuit. So I have narrowed it down to the power amp module. Because of the fuse incident i replaced the fuses thinking that they might be malfunctioning. Nothing changed though.

I can't seem to find any obvious problem with any of the solders or other connectors. The radio however doesn't seem to work either. Does anyone have any ideas as to where I should focus or what I should look for?It feels really bad to not be able to use the amp but what appears to be a minor issue and the budget is too low to send it for repair....any ideas?

Thanks in advance