rewiring a power supply

[elzmaddy]

After reading a few threads on Macintosh forums, I got the idea of replacing a Mac G4 Quicksilver power supply with an ATX power supply, since a replacement unit is very expensive (1/3 of the cost of the computer). This required splicing wires to match the mac motherboard connector, and the addition of an 24V adaptor to power the 25V line for the Apple ADC video. see an image here.

I flipped on the power strip switch, powering the PS (pin 14 is shorted) and the ac adaptor. The fan on the CPU spins, and a motherboard light powers on. The hard disk, however, will not start up with the motherboard connected. Also there is no video output.

I know my voltages for each connector pin are correct, but I have not checked current or paid any attention to rails. I don't know which Mac pin needs an independent +3.3V, for example, and which ATX wires provides it.

Any comments or suggestions would be appreciated.

 

[LiLithTecH]

A common problem with the G4 QS line PSU's was
the cooling fan failure. Did you check to see if that
is all that was wrong with the original PSU?

Which model G4 (Mirrored Drive Door, Digital Audio, QuickSilver 1, etc...)
There are differences in wiring pinouts between the models.

 

[elzmaddy]

I actually got it working. I connected the PS_ON wire to the MB instead of grounding it, then pressed power button

I didn't think to check the fan. Usually with a bad fan, the system will power normally, but overheats after a while, and then crashes. I didn't know a bad fan on a Mac PSU will prevent it from powering on.

(And it's an earlier Quicksilver, 733MHz model. I found the pin-out diagram here)