There may or may not be fuses. Every such piece of gear is different. The first step would be to chase down a schematic/service manual. Do you hear any hiss or anything at all out of the non-working channel? If you hear any noise indicating the amp is working, you might try a factory reset. Sometimes they just get "confused". But again, you'll probably need a manual to find out how to factory reset the thing. If you hear no noise at all, it's probably time to dig in.