My Rotel RA-931 integrated has an intermittent left channel. It occasionally cuts out or loses most of its volume. The key thing is this: if I crank the volume it'll suddenly come back and be okay for a day or so. Anyone have a suggestion on where to look?

I would prod and poke the channel with an insulated screwdriver this will cause buzz sounds. This should find the cause of the problem. Remember that the left hand channel is identical so you can compare the right with the left. For example if you get a weird buzz on the right when you touch it, but not on the left at the same point you might have found the faulty part.
Don't go near the power supply section as it's nothing to do with that the fault.

Try interchanging the speakers. If the right channel works, you have a problem with your speaker.

If it's an old type control then you can spray it with Servisol switch cleaner. You might have to take the top cover off to get better access.

Hi,
I think RA 12 is not existing type, but RA 12xx types exist.
Please try this link, and I hope you will find the relevant documentation.
Good luck!
gylacz

YOU ARE NOT RIGHT IT SHOULD GIVE AT LAEST A LOW VOLUME SOUND WITH A LOT OF DISTORSION AND A CRACKING NOISE IF DOES I GUESS THAT YOU HAD THIS AMP IN A PLACE WITH A LOT OF HUMIDITY AND YOU HAVEN'T WORK IT FOR SOME TIME IF I AM RIGHT PUT YOUR AMP IN THE SUN AND WORK IT FOR 10 MIN WITH A 5 MIN BREAK LET ME KNOW THE RESULTS

If your powered subwoofer could accept speaker level input, like, say a Klipsch KSW-series, you wouldn't need it.

Before we throw in the towel, turn it off and exercise every control a lot of times throughout its range, particularly the Tape Selectors. Sometimes oxides will develop on seldom used controls and their 'normally closed' contacts will not pass a signal.

Hi Nell. It is serious. Unless you are technically inclined, it needs to be checked out by qualified person. It will be fairly expensive to repair. Get an estimate.
Thanks
Paul

I'd suspect that one of the two output transistors on that channel has gone bad. If you are unsure how to test or troubleshoot this, then you might try replace both the NPN and PNP outputs and catch the bad one that way. If your amp uses an output module then you would of course have to replace the module which would replace all the output transistors on both channels. Good luck. Another thing to look out for, is the emitter bias resistors. They are the large white ceramic ones near the outputs. Sometimes one of those will open up too. They will be of a very small resistance value like .5 ohms (point five ohms) or something in that general ballpark, and have a wattage value of typicaly 5 watts. So they are pretty big resistors. Be sure to check them all even if you do find a bad output transistor. They will often go out with the transistor. Good luck.