I have an iMac G4/800 MHz/256 MB RAM/SuperDrive/60 GB HDD/GeForce2MX, bought in February 2002.

Recently the PSU died and now I have bought an ATX PSU 400W (thats all I could get).

Now I have to modify the ATX PSU to connect it to the main power connector on the Logic Board.

As far as I know, the connector is a 14-pin one and looks like this:
WITH THE CLIP ON TOP

RED, +5v, to HDD | YELLOW, +12v, to HDD | BLUE | YELLOW, +12v | YELLOW, +12v | YELLOW, +12v | YELLOW, +12v

BLACK, COM, to HDD | BLACK, COM, to HDD | WHITE | BLACK, COM | BLACK, COM | BLACK, COM | BLACK, COM

The only thing I can't figure out are the voltages of the BLUE and WHITE wires.

Does any one have a complete pinout for this model ?

I wasn't able to get one even with much googling.

Apple follows different color coding methods for different models of PSUs (I think).

I have connected the YELLOW (+12v) and BLACK (COM) from the ATX PSU to the iMac's main connector.

The iMac seems to show signs of life.

The only ones remaining are the BLUE and WHITE wires.

Mine is the lamp shaped iMac, the one that looks like a volleyball at the base and a sunflower on top.

PLEASE HELP.

Okay, the blue wire measures 3.6 V, so that has to be the 3.3 V rail.

The white wire appears to be the signal to switch on the power supply. It is approximately 12 V when the iMac is off, and then goes to zero when the power button is pressed.

This came as a surprise, because the G3 iMac motherboard puts out a high to the power supply. On my Jurassic SPARC I had to invert the signal so that the G3 logic would switch on a PC power supply.

http://yokenif.com/MacSPARC.htm

Hope this helps.