Two broken Fiio K9 Pro ESSes into one working unit.

[Konfl1kt]

Hello, people.
I have two broken FiiO K9 Pro ESS units.

1st: I hear white noise and faint music.
2nd: It is not being recognized by my PC, as if no cable is connected. The front panel does not work; only the LED lights function, and there is no reaction to any button presses.

I have disassembled both; visually, I see nothing wrong.
I would appreciate any help. I want to build one working unit from the two.

Thanks!

 

[Konfl1kt]

That is what is under the heatsink.

 

[Konfl1kt]

I'll share my thoughts here, and maybe someone can suggest some ideas.
The unit that is being recognized by the PC is the one I want to try to fix, because I suspect the issue is in the amp stage—somewhere under the heatsink and surrounding area.
To be specific, I connected it again and now I hear no sound at all in the left earcup, and constant noise with very faint sound in the right earcup of my headphones.
Any ideas what it could be? Can it be power supply?

 

[Konfl1kt]

Here is the thermal image of the unit.
I highlighted the area that gets hot almost immediately after powering it on.
How can I check this area? Does it look suspicious?
I’ve also attached an overall thermal photo.
Thanks.

 

[AnalogSteph]

To be specific, I connected it again and now I hear no sound at all in the left earcup, and constant noise with very faint sound in the right earcup of my headphones.
Any ideas what it could be? Can it be power supply?

Sounds more like a bad opamp to me. (What's the situation on the line outputs? Also, check headphone output for DC.) Either way, your strategy of starting with this unit makes sense. Fixing an analog fault is more realistic than swapping out a duff XMOS chip. I'll have to look at your pictures in detail to make sense of the circuitry.

What's your "tools and equipment" situation like? I suspect that with a thermal camera being present, you also have a half-decent multimeter with suitable probes. A scope might also come in handy.

I'd suggest looking for a good ground to clip to (XLR pin 1 might come in handy) and probing around on the supplies of the opamps next to the ESS DACs. You should find something reasonable like + and - 5 to 12 V, generally pretty much equal.