Onkyo TX-8050 AV-Receiver no sound

[ai.need.help]

Hello,

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:
pre-out
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!

[petehall347]

Re: Onkyo TX-8050 AV-Receiver no sound

first thing is check circuit boards for cracks ..most likely near to larger components .

[ai.need.help]

Re: Onkyo TX-8050 AV-Receiver no sound

Okay i will check that.

[budwich]

Re: Onkyo TX-8050 AV-Receiver no sound

what troubleshooting tools do you have? scope? DDM? test signal? You might try inputting a 1khz signal (computer file, cd or otherwise) and see / look for it at a few places along the signal path. Also check supply voltages at some "labelled" points on some boards depending on access under power.

What display are you seeing on the front panel? Maybe post a picture of the display to ensure what you are seeing, is what the forum will see.

[ai.need.help]

Re: Onkyo TX-8050 AV-Receiver no sound

I have a DMM and a 30$ DIY scope, but i think it would be not as helpful.
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

[petehall347]

Re: Onkyo TX-8050 AV-Receiver no sound

its most likely shorted after the regulator . disconnect whatever it powers and see if regulator works then

[budwich]

Re: Onkyo TX-8050 AV-Receiver no sound

looks like you are on the right track. It is rather "suspicious" that this type of fault happened with shipping.
As suggested, check to see if something "downstream" from the regulator is shorting the output. The quick check would be to unpower (disconnect main power) the unit and then do an impedance check (to ground) of the output pin in question. It should read some "reasonable" resistance. Go from the result.