If plugging into an effects loop return yielded nothing, and there is no sound whatever from that channel (ie: small hiss or hum) I would say there is no power from the power amp. Bad output transistors or a bad power supply for the output transistors. It would be helpful to have more info from inside the amp. Voltage reading and such. But if your asking for a tech right off I'll guess that you don't want to take it apart. I can't imagine a tech is hard to find in your area. I would probably call the music stores and ask who they think is good. Call any tech that gets mentioned more than once.