Beyond the usualy impedance checks---What are the switches on the back of the amp set to, for those chanels that do not work properly?

This amp has 6 separate stereo amps in it, and can be configured with switches to do several different things.

50 Watts per ch, x12 @ 8 ohms • 75 Watts per ch, x12 @ 4 ohms• 100 Watts per ch, x6 @ 8 ch, x12 @ 4 ohms• 100 Watts per ch, x6 @ 8 ohms bridged Dynamic Headroom: +1.9dB,

Configurable Input Signal Routing, Left/ Right/ Aux and Direct:Left Bus- Left channel(s) of theater
system, house audio distribution Center/Aux Bus- Center channel(s) of theater system, paging, tone signaling Right Bus- Right channel(s) of theater
system, house audio distribution Direct Input- Local audio or multi-room controllers Ability to combine any of the four bus signals together; makes simple mono
sound installations External control input - 6-24 volts AC/DC ground opto-isolated