Converting an ATX PSU to a BTX Compatible

Rescue your older power supply – Roy Dennis

Neither the author nor will be responsible for any direct or consequential damages to equipment or person if this procedure is followed. Proceed at you own risk!!

What with the new BTX form factor coming out, many of you are dreading the cost of all the bits you’ll need to buy to get a working BTX PC. I was looking at the BTX specifications and I noticed the motherboard connecter looked familiar. Sure enough, I called up the ATX specifications and found the motherboard connecters were similar, but not the same as the following diagram shows you:


ATX Connecter on the left, BTX on the right.

The only difference is an extra block of four pins on the bottom.

This means with a bit of work, you can make your ATX PSU work with your BTX motherboard.
First, you need an old/dead PSU so you can use part of its motherboard connecter as the extra four pins. Cut all the wires on the old PSU so you have about 5 centimeters of wire to work with on the connecter. Then, cut the old connecter with a hacksaw as shown in this diagram:


Now you have to solder the extra mini connecter to existing motherboard wires of the right voltage and splice them in. This is what you need to end up with:


Note the shapes of the plug pins and how they ensure you can only plug it in one way.

And this is how to do it:

For the COM wire, find another COM wire on the original connecter, cut it, strip the ends of the wire, solder them together and then insulate it (heat shrink tubing or insulating tape). You’ll end up with something like this:


Do the same to the other connecters. Then double, triple check what you have done. Getting someone else’s opinion also helps here. Even if they don’t have the first clue about electronics, their questions help you spot mistakes. If it’s wrong, you’ll cause a very nasty short circuit somewhere and kill something somewhere (hopefully only the fuse in the PSU). You have been warned.

Also note there is a 5v feed to the ATX plug which is different to the others – it’s denoted as 5VSB. This feed is always on; it powers the motherboard even when the computer is turned “off”.

Do not use this on the BTX mini connecter. I cannot stress this bit enough! Ensure that it looks exactly as in the diagram shown – if the square and house shaped plugs are orientated the wrong way compared to how you wired it, you will end up putting it in the wrong way round and giving the wrong voltage to the wrong things.

Last note: The new COM wire on the BTX connecter used to be a PS_ON wire and is often quite thin. If you can, you might want to try and directly solder the COM wire directly to where the PS_ON wire is connected to the plug contact so any current flowing doesn’t end up flowing though a wimpy little wire. This, however, is almost certainly not necessary, as all the COM pins are connected to each other on the motherboard anyway.

Good luck!

Roy Dennis

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