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Apple G4 Power Supply Woes?
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."
I have the same problem with my pc. I've had it since july, and i think it is based on humidity. when i crank the AC up in my room and close the door, it will take about 20-30 mins before it will start. it's not the temperature because it can be 60 degrees in the room, but will still not start if the humidity is too high.
You might be surprised. Sometimes they wil even do free service on out-of-warranty products if its a 'known issue'. My 5-year-old Blue&White G3 monitor died a few months ago. It was making sparking noises and a funny smell when you turned it on. I called Apple up, they said it was a known issue and shipped me a new one for free. It sounds like you are past the point of being able to fix it yourself. If you haven't already, try checking the Apple Knowledgebase, and removing cards as was suggested above. If it still fails, take it to a local Apple repair shop.
Don't know about G4s or desktops, but I'm now on my third dual-USB iBook external power supply. First replacement was covered by the warranty, but I just shelled out ~$85 for the second replacement today at the local Apple store. And the main logic board had to be replaced three months in. AND the little twist lock on the underside that releases the battery is broken and held in place with scotch tape. I love this laptop, but the build quality is not good.
After submitting the question, I resumed scouring the web and got a bit braver with my parts...
o 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.
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_c
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.