ATX to AT power supply conversion

May 04, 2007

Any true computer geek has a couple of old AT motherboards in their closet. I have quite an affinity for the babyAT specification, but unfortunately, most AT power supplies (including the one I had) are way to big to make any cool use of those babyAT boards.

So during an afternoon of rain and the need to procrastinate real work, I decided there had to be a way to use a tiny ATX power supply on an old AT board. Since the only basic difference between the two is that ATX introduced 3.3v rails, I knew it had to be a simple re-arrangement of pins to an old atx connector.

Tools for the Project:

Tools for the Project:

  1. Soldering Iron
  2. Solder
  3. Pliers
  4. Xacto Knife
  5. Old AT connector
  6. New ATX power supply
  7. An ATX female connector and pins
  8. Multimeter

Basically cut the AT connectors off of an old AT PSU.

Follow the diagram below in wiring the AT connector to your ATX female connector.

Wiring Diagram 1

Wiring Diagram 2

Then of course test with a multimeter. Plug everything in and when your PSU is plugged in, the AT system should power on. The one thing to take note of, is that if your ATX power supply doesn’t have a power switch on it, the AT system will power on as soon as you plug the system in. This might be bad, so it’s recommended to only use ATX power supplies with manual power switches on them.