Acolyte of the Butterfly
Posts: 105 from 2019/11/1
For Powermacs G5 you can try to boot with only one cpu at time.
In your maintenance disassembly/reassembly you can have damaged something like cpu socket/cpu board.
Be sure your cpu is in full contact with its heatsink.
I have rebuilded from scratch G5 quad LCS with custom parts, I know manage powermac parts is not a joke, it's completely different beast, not sure an usual pc.
Try also to reset pmu and spu and change cr2032 battery.