RME ADI-2 DAC FS-- All Outputs Heavily Distorted, Levels Diminished

[Scrivs]

My very favorite component needs a bit of help. Bought it used about 3 years ago, it's given me many hours of faithful service, and truly is my favorite bit of audio kit. The trouble started a couple of days ago. Presents as such:
Audio on ALL outputs is lower than it should be, and massively distorted. Pops and clicks are evident not only on startup/shutdown, but also happen randomly. This behavior is present in BOTH lineouts (XLR and RCA), AND BOTH headphone outputs (6.3mm and IEM).
The low output and high distortion is present regardless of input (USB/Coax/Optical).
The problem occurs independently at all gain settings. All Windows audio enhancements are defeated, I keep the Windows "Volume" slider at 94. Adjusting it makes zero difference. My Motu M4, SU-9 and DEQ2496 are all working perfectly-- problem seems to reside in the RME

I updated the driver to the latest (1.08), and the FPGA/DSP versions were also updated to the latest: 81 and 62 respectively.

While monitoring levels on the device itself, nothing looks out of place--levels are fine, no overloading. It seems everything on the input side is fine, and the problem is common to all outputs. At first I thought maybe a muting relay or transistor was the problem, but not when all outputs are exhibiting the same problem.

I'm leaning more towards a hardware problem-- a component upstream of, and common to, all the outputs. Any and all suggestions would be massively appreciated, I can't afford to get another one, but have a bit of experience with analog electronics testing/troubleshooting, and know my way around a DMM.

Thanks guys and gals, and, happy holidays!

 

[MC_RME]

You could verify the 12 V power supply stil works correctly when connected, with your DMM, but as the ADI-2 DAC displays a warning for undervoltage I expect the ps to be ok. So this looks like an internal power supply issue, where for example the voltage for the DAC or the analog output stages is not as it should be.

If you really have experience then I don't have to tell you that checking all opamps for +-15V operating voltage and the voltages around the DAC chip as well as the output signal of the DAC chip is quite easy...

 

[Scrivs]

You could verify the 12 V power supply stil works correctly when connected, with your DMM, but as the ADI-2 DAC displays a warning for undervoltage I expect the ps to be ok. So this looks like an internal power supply issue, where for example the voltage for the DAC or the analog output stages is not as it should be.

If you really have experience then I don't have to tell you that checking all opamps for +-15V operating voltage and the voltages around the DAC chip as well as the output signal of the DAC chip is quite easy...

Thank you very much for the reply. Yes, the outboard SMPS is fine--12.16V. I checked all the available test points on the board, the most of the supply voltages all look good: 1V8, actual: 1.79V. +3.3V, actual 3.29V. +1.2V, actual: 1.19V. 5VA, actual: 5.0V. However, measuring across the -16/+16VA TP, I'm measuring a fluctuating voltage of 13-14.5V. Close, but a bit low, and unstable. Next, measuring across the -15/+16VA TP, I only get around 5.7-6ish volts. Poking around a bit more, there's a diode located above the -15VA TP which appears to have failed.
The supply voltages for the AK4490 all measure within limits.
It appears the problem is somewhere n the negative supply rail for the opamps. There's an LED located next to each of the +/-15VA test points, only the +15VA one is on. Am I correct in thinking that both LEDs should be lit to indicate correctly functioning rails? Am I on the right track?
Throwing in the towel for now-- my 49 y/o eyes are failing me as I'm working under a magnifying glass. Mr. Magoo style
Thank you very much for responding, I really appreciate you taking the time to do so. This DAC is one of my Favorite Things (literally), and I'd like more than anything to get it up and running again.
Mahalo nui loa from Hawai'i

 

[MC_RME]

Yes, the other LED should be lit, means -15 VA is down. You have to measure the voltage from TP to chassis ground, then can tell which one fails. If -16VA is already too low there could be a short in a later section. Between TP -16VA and TP-15 VA is a discrete Low Drop Low Noise regulator circuit which might have failed. Or the issue is even later, for example in the headphone stage, drawing too much current...but then the display should show a warning. Unfortunately from here on it's getting complicated and requires mods to the circuit to measure the currents...

 

[Chazz6]

If a diode, opamp, or such failed, or if a joint failed, or if a trace broke, taking all these possibilities together, what would cause such a failure?

 

[Scrivs]

There's a PSOP-8 device aft of the V-test header (when looking from the rear of the PCB. It's a 150mA LDO labeled2204MP
ADJG1. Is this what supplies the OPAs on the +/- 15 VA rails. Going to bed now, will measure tomorrow. Thanks again for the suggestions.

 

[MC_RME]

No. The +-15V regulator is around the +-15V test points, with one OPA1602 in the middle. The +-16V are generated at a point far away.

 

[Scrivs]

From the power supply above the Spartan I.C.? The upper left side of the board? That’s where I traced back to tonight, but haven’t checked the data sheet for the 16 pin device located between the inductors on the edge of the board.