i am new to mac-modding and normally work with linux, so excuse any nescience about mac-specific stuff. ;D
I have a iMac g4 800 with the 17" tft. Unfortunately the power supply is not working. Now i soldered a 400W ATX supply to the small power connector with the 14 pins and it looks good, as i have 12v on the backside of the logic board as stated in the apple troubleshooting guide. but when pressing the power-button on the mac, the atx-supply gets switched off. the fan is moving a little bit, so power gets through the logic-board. Now i don't now if this is because of a safety switch in the power supply that shuts it down when there is requested so much energy (as the supply can supply 20A on the 12V line, but only peak, which is more than the mac supply, but thats much of energy ;-)) but i personally think that it is a problem with connectors, that i forgot some soldering or sth like that. i only connected the 12v and 3,3v lines with the corresponding lines from the connector, no extra wiring. perhaps the mac needs some extra wires for the switch on and sends a atx-shutdown. i read something with a 12v line that has 12v when mac is off and is sut down to 0v when mac is on. this is sth a atx-supply is not providing i think ;-)
Never messed with the PSU from a G4 iMac. I think I've only ever replaced one of them. It tend to be the logic boards which die in those so you really shouldn't struggle to find a replacement without spending a fortune.
Loc: Florida, USA
I find it werid there isn't any +5v lines going into the logicboard. You could always make the power supply turn on by installing a switch for the green (power on) line to a ground. Basicly making it run as a AT power supply.
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