This is an email sent to me by Derek Schacht <dschacht _at_ gmail>.

First off I am a Computer Engineering student at Virginia Tech. I have a huge love for Macs and have been using them for about 15 years. I thought you might find this interesting.

I recently acquired a Dual 1 Ghz G4 (Quicksilver). When I got the computer the power light would come on briefly and the fans would spin until the power cord was pulled. After testing the power-supply it seemed to be ok. I figured either the cpu module or the logic board was gone.

I bought a new logic board and cpu on ebay. After installing these items the computer booted once. However, after turning it off it refused to boot again. I troubleshooted for a few hours to no avail. Tonight I decided to see if I could get it to boot again and I thought that the power-supply might be to blame so I converted an old ATX style power-supply.

After doing the conversion and hooking it up the computer still would not boot. After trying it a few times I booted the computer once while my hand was on top of the heatsink. For some reason the computer booted and ran fine for about 30 min then I turned it off again. And tried to boot it again it refused. But if I put my hand on the heatsink it boots right up.

Initially I suspected a grounding issue so I ran grounding wires to a few key places including the heatsink but to no avail. However the computer will almost always boot if I touch the heatsink.

The computer still refuses to boot from the original power-supply.

Original Power Supply -- Original Logic Board -- Original CPU --        No boot
Original Power Supply -- ebay Logic Board -- ebay CPU --                No boot
Original Power Supply -- ebay Logic Board -- Original CPU --            No boot
ATX Power Supply -- Original Logic Board -- Original CPU --             No boot
ATX Power Supply -- Original Logic Board -- ebay CPU --                 boot (with hand trick)
ATX Power Supply -- ebay Logic Board -- ebay CPU --                     boot (with hand trick)

My conclusion

Original Power Supply           Dead
Original Logic Board                    OK
Original CPU                            Maybe (I don't think it likes the ATX)

ebay Logic Board                        OK
ebay CPU                                        OK

Posted here in case it helps anyone else!