ATX Power Supplies in Macs

1 reply [Last post]
Joined: Jan 28 2004
Posts: 60

It's around at some sites but I thought I'd post it anyway.

To use a ATX power supply in some Macs the /PFW Power Fail Warning
Mac pin needs to be inverted and connected to the ATX PS-ON pin.

This will work in old 68k macs like MacII's as well as PPC macs.

Any mac with a /PFW Power Fail Warning pin should work.

The /PFW Power Fail Warning pin goes high when the mac is switched on
but the ATX PS-ON pin needs to go low.

Also connect the +5v in the pict to the ATX Stand By pin.

All other connections like the +5v +12v etc are straight forward.

If you use a Cmos 74HCT04 instead of the 74LSO5 you don't need
any resistors.

Here is a transistor based invertor

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Joined: Dec 20 2003
Posts: 851
You can ignore PFW. It's onl

You can ignore PFW. It's only purpose is to tell the motherboard that the supply will be dropping out very soon. You can also ignore PS_OK as it only is to tell the board that the lines are up and stable and safe to come online.

All you really need to do is short PS_ON to chassis ground when you want it on and then open it when you want it off.


Dr. Bob
Applefritter Admin