RCF HD10A mutes bass channel after several minutes

[Martin355]

Hello,

I am trying to figure out if there is someone who has a schematic for RCF HD10/HD12/HD15 or has some deeper knowledge how to debug no audio issue.

Amplifier starts up and is able to play audio from both channels - tweeter and bass.
Depending on load amplifier mutes bass channel. It takes 15 seconds (full volume level) to half an hour(low volume level) to reproduce the issue starting from the room temperature.
All the LEDs stay in initial state(STATUS led GREEN and LIMITER led witched off). Tweeter channel keeps to play audio.
So far I have measured DC voltage level on 2 largest capitors and it stays constantly +112V on one leg and -112V on another leg.
Woofer passive resistance is ~4ohms, I could not detect abnormal overheating on the amplifier PCB.
Would like to avoid replacing the whole boards.
I am grateful for any help.
Martin

[Martin355]

Short update. I was able to verify that IRS 20955 MOSFETs driver chip CSD pin (shutdown) stays high before and after error occurs. Also valid digital audio signal is present all the time between pins 3 and 4. Replaced IRS 20955 (upgraded to IRS 20957) and also both IRFB MOSFETs, but issue is still present.
I am pretty sure that the error in only related to the output stages.
Any ideas which capacitors, diodes to check first?