I have a 6 zone system using a PA1235. Everything seems to be working fine, except on zone doesn't put out any sound. I tested the speakers, inputs, etc. I plugged in known working speakers and a known working input and still nothing. The light on the amp for that zone comes on and off properly, but no sound. The amp is only 4 months old. Could 1 of the amps burnt out?? I can think of anything else to try.