Thanks to everyone for taking the time to reply.
Bsamooa, special thanks for your detailed questions and suggestions. To respond briefly: (1) there's no noise (e.g., boom or scratch) at sound cut out; (2) after sound cut out, no hum or hiss from the quiet channel; (3) I haven't tried listening after sound cut out to both speakers without music playing.
Bsamooa and noromance, I'm going to show your post to the repair tech. He said he couldn't duplicate the problem so he couldn't diagnose it, but perhaps your post will give him some ideas. If not, I'll bring the amp home, put it back into the system and when (and if) it fails again, I'll come back here and see what can be tried.
Bsamooa, special thanks for your detailed questions and suggestions. To respond briefly: (1) there's no noise (e.g., boom or scratch) at sound cut out; (2) after sound cut out, no hum or hiss from the quiet channel; (3) I haven't tried listening after sound cut out to both speakers without music playing.
Bsamooa and noromance, I'm going to show your post to the repair tech. He said he couldn't duplicate the problem so he couldn't diagnose it, but perhaps your post will give him some ideas. If not, I'll bring the amp home, put it back into the system and when (and if) it fails again, I'll come back here and see what can be tried.