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Apple G4 Power Supply Woes?

Posted by Cliff on from the don't-taunt-happy-fun-power-supply dept.

Predius asks: "I, like many others based on forum hopping, have an Apple G4 desktop that has decided it no longer wishes to power up. I've replaced PRAM batteries, verified power supply voltages, pressed the CUDA switch, and done combinations of the above. Trying to start it just results in a blip of the powersupply fan and the power led on the motherboard flashes once. Every now and then it will actually boot, and when it does it's 100% rock solid, will reboot fine, etc. If I power it off, I get to play games again trying to power it up. Does anyone know how to manually start an Apple Gigabyte or later rev power supply? Standard ATX power supplies can be fired up by shorting the green PWR ON lead to ground, but Apple decided to be different. I await the collective's wisdom."

1 of 152 comments (clear)

  1. It was indeed the power supply in my case by Predius · · Score: 4, Interesting

    After submitting the question, I resumed scouring the web and got a bit braver with my parts...

    After reading up on some G4 to PC ATX case conversions, and doing a lil guessing, I determined that the G4 power supply should use the same power up sequence as an ATX. What threw me off is earlier PC ATX power supply to mac conversions had to invert the power on signal, and I incorrectly assumed Apple did the same with the G4.

    http://www.xlr8yourmac.com/systems/ATX_G4_AGP_co nv ersion/G4_AGP_to_ATX_case_pg2.htm has the mods that get you 99% of the way there, you just need to supply 28v to finish the job on any ADC capible G4s. Once I figured this out I had the system booting off a PC power supply (and the 28v trickle from the G4 supply). I bench tested the G4 supply, and sure enough, shorting the power good, which should have fired it up just bliped the power. Based on the symptom set, it seems pretty likely this is whats affecting others. The test is simple, use a paperclip or something similar, short the green power up line to a black ground line, and see if the power supply fires up. If it does, it's the mobo, if it doesn't, its the power supply. No more throwing batteries sacrifical virgins at the problem while performing dark rituals around the CUDA switch.

    And for those curious, the machine I'm building is a FrankenMac, assembled from random bits on eBay and my parts closet. I've TRIED talking to apple stores, but the instant they figure out its not a boxed apple, they tell me to pound sand. I've got $75 into the power supply, so I wanted to be ABSOLUTELY certain it was the culprit before canning it. Unfortunatly, while Apple will offer some simple diagnostic guidelines, they won't give you all you need to do this sort of work outside of an Apple authorized repair depot.