NS-R5101HD same as Pioneer VSX-819H-K Receiver

Was working perfectly fine for many years. 5.1 setup with Paradigm Atom speakers and Sony sub.

Connected to TV via SPDIF cable.

One day sound "popped" and now LED shows volume  numbers go UP and DOWN(knob or remote), but sound level stays the same.

Sound is distorted and when plugged in headphones, one channel only.

Tested all transistors on the AMP board, - nothing shorted or open. Tested all diodes. Caps seem fine.

Same tests with main board.

All voltages are seems there.

The rest of the boards tested the same also...

Any help is highly appreciated.