Losing the right channel

https://elektrotanya.com/nad_c370_sm.pdf/download.html

https://music-electronics-forum.com/forum/amplification/other-amps/920148-nad-c-370-no-sound-from-speaker-outputs#post920172

https://audiokarma.org/forums/index.php?threads/nad-c370-repair.916194/

NAD 355BEE SM Service Manual free download schematics eeprom repair info... http://elektrotanya.com/nad_c-355bee_sm.pdf/download.html

Possible output power transistor issue. Always use factory parts and use matched pairs.

If swapping of left and right input sources and left and right speakers does not help...you might have a bad channel in your amp.

This could be as simple as a bad connection at the voltage regulator IC or blown output transistors. If you have a multimeter and some experience with electronics repair, this should be fairly straightforward.

Let me know and I'll try to walk you throught the repair.
Dan

Sounds like you have lost the power amp transistor(s) or IC for this channel.

Only the right channel had a sound,the left channel is mute, whatever adjustment you did and whatever balancing you done nothigs happen,even you interchange the speakers. The problem is in the power amp. The STK IC there is busted already, it's better to change it with a new one so the performance become normal again.

Check all your cables, not likely but just in case.
Try removing all but two. Left and Right. Does it still happen,
If you can identify the speaker channel try swapping the speaker if possible.

It sounds like one of the speakers has an issue, could be a short in a cross over or speaker coil. If true the speaker is drawing too much current and causes the protect circuit to trip.

Depending on the quality either replace the blown speaker driver or purchase new ones.

If the speaker is not the issue it could be an issue with a power amp. Best to take it in for service.

It is most probably a dirty speaker protection relay. gently tap the relay(the one that engages shortly after turning the amp on) when the fault is occurring and see audio returns. This should ascertain the problem. Replace it if it is a sealed type, or if it has a "lid" you can get off, burnish the contacts with a white business card, and give it a spray with contact cleaner/lubricant. Good luck and a "fixYa" rating would be great for my profile :)

possible short in speaker system. Disconnect the speaker to that channel. if it does not click off then you have a short outside the amp in your wiring or in the speaker.