Sux when the good stuff finally needs servicing and we discover that the world has turned into the age of just 'throw it out and get another one'. My PLC robotics guy will repair anything with a circuit board or even tube stuff as a hobby on the side.
If the channel is dead dead perhaps there are fuses on the pc board? Just suggesting because the higher output amps had that. I changed out my Marantz receiver for a Woodson solidstate 4 channel amp back in the 1970s because the Woodson had front panel mounted fuses and I could use any tuner with just a pre-amp output. I lucked out because I also scored 4 cerwin-vega stage speakers with the amp when a local production company folded.