Frank van der Hulst wrote:

John wrote:
I think you'll find that the -12V is used only in "legacy" PC design for
ISA busses, or serial ports (which he probably isn't using).

What is the +12 vdc for?

serial ports, fans and disk drives mainly

And nowadays CPUs.... late last year I upgraded a PC motherboard from
800MHz to to 2.4GHz by replacing the motherboard. The new motherboard
had an extra connector to provide 12V to the CPU 9Celeron, IIRC), so I
had to replace the power supply as well. I'm guessing that the CPU had
onchip regulators to provide the other voltages that it required.

Frank
Thats true. my athlon 64 bit has it too. it was originally for the P4 chip.
Although the project that was the focus of this thread delt with a mini-atx
case that does not have this. For that matter he was not using any disk
drives instead he's using an USB thumbdrive. so he probably could get away
with leaving out the 12v. I've never tried it so I don't know. Maybe this
weekend I'll pull out one of my older atx boards and see if I can get it to
boot without the other supplies.
John
PS Don't forget to emulate the pwr good signal!