Have a buddy whose JBL PSW-1200 recently quit outputting sound. The light on the back of the sub lights red when plugged in, and there is a thumping noise when the sub is plugged in or unplugged. Otherwise, nothing. He's out of warranty, so we cracked open the box last night. Pulled the speaker out, it's working when plugged into another source, and the removable fuse seems to be intact and good as well. I've downloaded the service manual and owner's manual, but don't have a lot of the fancy equipment to test all the connections. Any advice on where to go from here?