PM 6100/60, was: Powermac G5 won't start

My apologies for tagging along, but there seems to be a few people who know about these PPC beasts. I've got an old Performa 6100/60 (the first Power Mac if I read my Apple history right0. It boots and seems to run just fine, but there's no sound--nothing, not even the power-on chimes. Control panel says that nothing's muted and the volume is up full. The PRAM battery is new; I was able to check that the speaker and audio amplifier work by injecting a small signal into its input. Beyond that, it seems to be Apple proprietary VLSI or custom chips Does anyone have a clue? I'd refer to my 6100 schematics and chip datasheets, but of course, there are none. Apple's "if it doesn'''t work, buy a new one" philosophy, I guess. --Chuck