Question Onkyo TX-8050 not playing music

Dec 20, 2022

I have a problem with my Onkyo TX-8050 Receiver. I got it from aftermarket and it was just delivered today.

It doesn't play music. There is no real output from:
amp-out A and B
phones out

The only real sound I hear is a humming from the speakers when I play a song from usb or select a analog source. And when stopping and starting songs from usb or switching sources, I hear a crack from the speakers.

I tested with analog-input, usb and radio.

I know that there is a common problem with the dsp with certain onkyo devices, but I don't think it has the corresponding symptoms. I have both of the menu points "network configuration" and "firmware update", usb devices are loading and the relais for amp group A and B are working (clicking when turning one group on or off).

The previous owner says it worked and I trust him. It maybe was a damage during the delivery even tho it was protected very well in the package. But where can the problem be? Can you help me?

Thank you very much! :)
Dec 20, 2022

I traced the problem down to a voltage regulator, but I'm not sure if it's the source of the problem.

Here is a service manual for my receiver. If you want to follow please download.

On page 10 (SCHMATIC DIAGRAM - 5 - POWER AMPLIFIER SECTION) in sector 7E, you can see the voltage regulator 78M15A from jrc (named Q911) and another regulator 79M15A (Q912). I got the data sheet for the Q911:

It gets 22 volts and should output +15 volts. But i measured 40mV on pin-out and it gets really fast really hot, around 96° Celcius (205F) measured with my temperature sensor from my dmm.
Power comes from the rectifier D922 (model S1NB60) which I assume is OK because both regulators Q911 and Q912 get the required voltage for operating.
The other voltage regulator Q912 for outputting -15v works fine.

I'm not a pro in reading circuits but i believe these voltage regulators should deliver their output to the AUDIO INPUT SECTION on Page 9. The big chip in the middle gets +15 and -15 volts. I also measured a +15v trace going there and there is also the 40mV on it.

So I am assuming the chip doesnt get power and therefore not outputting any audio to the amp-section, is this right? Is my problem fixed when I replace the faulty regulator? Or can there be another problem in front of the regulator?

btw. I checked the fuses and they are OK

sorry for my bad english, I'm not a native speaker:)
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