How to modify an ATX power supply to always turn on after power loss: Update: I have encountered a couple of motherboards that this howto does not actually work on. Not so much that the power supply doesn't turn on when power is applied (it does turn on and the fan spins), but infact the motherboard doesn't actually boot unless the power switch circuit is shorted (the power button is pressed).

The motherboards I have seen this occur on are made by PCChips (which is one of the cheapest motherboards on the market currently, and do not support power on after power failure in the BIOS, which is the point of this howto).

I did devise a way to get these motherboards to boot up. By placing a capacitor (the microfrad rating escapes me, but I seem to recall it was in the 15 microfrad range). What the capacitor does is provides a momentary contact between the postive and negative poles of the power switch which causes the motherboard to boot. The only problem with this method is that there is a delay that needs to be introduced between the power off and power on cycle. This gives time for the energy stored in the capacitor to disipate so that the next time the motherboard gets power, it provides that momentary contact again.

I hope this additional information will help somebody else.

Update 2 (Feburary 20, 2008): I received the following humorous email today and I had to share it:

Hello, just wanted you to know that following your tutorial on ATX power up I justed fried my motherboard. Damn you, mother****ers! Burn in the lower regions of THUD forever! Just kidding. Actually I sucessfully shorted the ATX pins on my PCCHIPS M810DLU (with a paper clip. Children, do not try that at home) powering my home Slackware server and it works like a charm! Server auto powers up fine =) I'm emailing you because you state that the mod doesn't work with some PCCHIPS mobos and I thought you might want to add that at least with this particular model it seems to work great! So, thank you very much!

So there you go... if you are using a PCCHIPS M810DLU motherboard, this mod will work without the capcitor trick mentioned above.

Disconnect the plug from the motherboard.

Orient the plug so that the clip (the one used to secure the plug to the motherboard) is facing you.

Working from the left, the 4th wire should be a green wire. The 3rd wire should be a black wire. These wires are numbered 14 and 13 respectively in the ATX power supply spec.

Cut the green wire close to the ATX plug. We are going to use the power supply side of the green wire, so the plug side needs to be capped.

Splice the power supply side of the green wire into the black wire (13) on the plug. The black wire must remain connected to the plug. We use a splicer called a "tap splicer" (the blue item pictured in the pictures). What this does is take a wire (the green wire in our case) and splices it into another wire with out cutting the other wire. In the past we have used but connectors and shrink wrap as well.

Plug the ATX plug back into the motherboard.

Plug the power supply into the outlet and the computer should turn on instantly.

Here are some updated picutres of a server I recently took out of production that had this modification done to it.

The quality on these photos is much better than the ones above so maybe they can help you get a clearer understanding of what needs to be done.