Any1know what might be wrong w/ my Nakamichi PA 1

The power went out the other night and when it came back on a second later the rear channel wasn't working on the amp. It now makes a little switching/clicking sound. I had it connected to a APC C5 power filter and thought that was protecting my equipment/ that it was working just fine. Perhaps not. Perhaps something else happened i don't know. Does someone think they may know if it's a serious issue or something minor? There are no fuses under the hood that can be changed for a easy fix i noticed. I'm kind of at a lost when it comes to fixing electronics myself. Thanks for any help. It's such a sweet sounding 5 channel to have to dump.