Onkyo TX-NR828 repair

[ubis]

Hi,
I've got an Onkyo TX-NR828.
Some short backstory: it was advertised as "it won't turn on". Once I've looked inside, some cables were not properly plugged in.
After this, it turned on, however there was no sound. Even if input is connected to something, once receiver turns on, it shows "No Input".
So I've started to disassembly it and I've noticed, that board is broken at some places, disconnecting some of pcb wire traces. I've soldered wires to broken traces.
After turning it on, I've noticed a heat coming from 7815 & 7915 regulators(In schematic it's Q4170 & Q4171). Soldered them out to check them and....
I've fed 7815 with 18V and it's output pin had like 17-18V. 7915 wasn't broken.

The cause of this was a shorted relay. Main transformer has 2x21V and 2x50V and these relays are used to either power it with 2x21V or with 2x50V.
One of these relays had a short on all of 3 terminals. 2x21V is used to feed these 7xxx regulators. So instead of 29VDC, 7815 received about 71VDC...
I've soldered a new 7815 and now I've got stable +-15V power supply. It seems like amp is powered by default with 2x21V, since I haven't received new relay yet, I've shorted 1 & 3 pins.
However, the voltage drops from 21V to 10V on this side, diode bridge is fed with 21VAC and 10VAC... But after diode bridge it's nice +-29VDC.

Still, no sound. With a scope I saw that signal wont go past Q4001 which is digital audio input selector R2A15220FP. So I thought: great, probably it received more than +-7V since that
7815 regulator failed before. Also that chip was hot. Today I replaced the chip and... Well now receiver doesn't show "No Input" at startup. And I can hear music, but... When volume is 40% or more.
Though chip is hot as previous one was.

This is nice 1KHz sinewave near Q4001's input pins:


This is what I'm getting from Q4001's output pins(FR, FR, etc...):


And output from the amp:


It's the same with other inputs. Everything seems to be working just.. That gain is reduced a lot. And that voltage drop is wierd aswell.

Input stage in service manual to look for: page 27 (SCHEMATIC DIAGRAMS-04(PART-4))
Power stage where one of relays failed: page 28 (SCHEMATIC DIAGRAMS-05(PART-5))

Service manual - https://ufile.io/15ecr

I don't know where to look now. For some reason Q4001 chip is reducing the gain. Maybe I've received defected one from aliexpress..?

[kjk24]

check the preamplifier boards, i have the same on a onkyo i dont remember the number but it wars a NR...
i removed all preamplifiere boards, and the signal wars ok after the chip.
its a lot of work to remove them but ... you can then insert it step by step and find the bad one.

[mzacharias]

Gain may be normal; check the surround modes? Try stereo only or stereo direct? No telling how it was set up before - maybe try a factory reset.

[ubis]

Yeah, I already did the factory reset and played a bit with pure audio mode / other sound modes. It could be that my speakers are not that sensitive. I guess that's it.