Good point, Sir Quack, and if he doesn't have a CD player or MP3 player, he could unplug the sub cable from the Sub Out pre-out and just touch the center prong on the RCA jack. If the subwoofer amp is working, you'll get a loud buzz from the subwoofer. If no buzz or low-frequency hum when you touch the center prong, then the subwoofer amp is at fault. The sub has to be ON, of course, to do this test.

Alan

Alan Lofft,
Axiom Resident Expert (Retired)