[bill-e]

Pry the bezel off and it will expose 4 screws. Remove them and you can slide the unit out.

I doubt that there is any user serviceable parts, if it worked before it's probably the C channel output that gone bad.

I had the same unit and it crapped out within a year, I would have to let it warm up on channel "C" for 40 minutes before any sound came out. Got the unit replaced under warranty.