Written by: fwaggle
Converting an ATX PSU to full-time
I needed a PSU to power the mammoth Seagate hard disk for my Indigo2. With an ATX system, the motherboard will pull the PS_ON wire low by connecting it to ground, and the PSU will power up. It's actually quite trivial to cut the motherboard out of the equation and tell the PSU to stay on by simply shorting this wire to ground.
Yes, I know this has been explained many times before. I'm listing it here more for my benefit.
If you look at any ATX pinout diagram, you will see the connector layout if you were looking down at the board. With the PSU unplugged from the wall, choose any of the COM wires which should be black, and cut it. Now look for the PS_ON wire, which should be green and is often thinner than the rest, and cut it too. Strip both wires about a 1/2 inch, and twist them together. Solder them together and cover with electrical tape. Alternatively, if your PSU doesn't have a 120V switch on the back of it, you can choose to switch this connection to let you toggle the power on/off.
Not really much to it. Plug it in and you should have full time power to all the molex connectors. As some others have done, wire it up to a couple of banana connectors and they make a pretty good low-amperage desktop power supply.