Cary Cinema 6 problem

I just recieved a Cary Cinema 6 bought used off of an alternate site. It was advertised as "good working condition" but all I get is a load POP from the speakers then the amp goes into protection mode. This happens with any source - digital, two channel analog or 7.1 passthrough. I get no sound whatsoever other than the POP. Before I return this unit, what could be wrong? I got it for a great price (maybe too good to be true...) and would rather put a small investment into getting it working rather than returning it if all it takes to get it working is a small investment, not a large one. I pulled the cover and found the unit to be VERY clean! Both fuses are good but there is room for four, but missing fuses won't cause a POP. No obvious melted wires. No scortched areas. Any thoughts on what to look for? What to test?