In future you can identify channels with a battery. Or ring out the wires with a multimeter.

If you are out of warranty crack the case and check for blown fuses. Probably a couple $ fix. I dont know how handy you are, but usually if it is an easy fix it is worth doing yourself. smile Hope its something simple.

Oh yeah, dangerous voltages are present when plugged in. Unplug and let sit a few minutes while the caps fully discharge before you poke around. wink