You just need to replace monostable power switch mounted in your case with bistable and connect it to ATX 2 AT power cable adapter.

Locutus wrote on 2026-01-18, 12:01:

You just need to replace monostable power switch mounted in your case with bistable and connect it to ATX 2 AT power cable adapter.

or translated into english, replace momentary switch with latching switch

Ok thank you, I have found a latching switch on Amazon.de

You could also short the power switch cables on the adapter and use the ATX power supply's power switch (assuming your PSU has one) to start the system.

I did that in a pinch until I had proper toggle switches.

fosterwj03 wrote on 2026-01-18, 23:23:

You could also short the power switch cables on the adapter and use the ATX power supply's power switch (assuming your PSU has one) to start the system.

I did that in a pinch until I had proper toggle switches.

yes, this is my plan to test whether the board really functions or not.
=> all my atx power have a power switch, I m lucky 😀
after that I will buy the swith from amazon, thank you 😉

Using an ATX supply on AT board...

First, the adapter, does it short power good to turn on ATX supply right away or does it have a 2 pin header? Or maybe a jumper? If it has a jumper or a 2 pin header you should be able to put ATX power switch to that header/jumper and turn on and off with the case switch.

If it doesn't, and is hardwired to turn on, use an ATX supply with a rear power switch or use a power bar with an off switch.

Latching switch will do you no good in this situation unless you have a qualified electrician make a mains power switching cable extension from the supply like the old AT supplies had.

Edit: the latching power switch, of correct 4 pin type for AT cases, would be required if putting an AT supply into an ATX case, for an AT board, NOT required for ATX supply in ATX case with AT board.

BitWrangler wrote on 2026-01-19, 16:58:

Using an ATX supply on AT board... […]
Show full quote

Using an ATX supply on AT board...

First, the adapter, does it short power good to turn on ATX supply right away or does it have a 2 pin header? Or maybe a jumper? If it has a jumper or a 2 pin header you should be able to put ATX power switch to that header/jumper and turn on and off with the case switch.

If it doesn't, and is hardwired to turn on, use an ATX supply with a rear power switch or use a power bar with an off switch.

Latching switch will do you no good in this situation unless you have a qualified electrician make a mains power switching cable extension from the supply like the old AT supplies had.

Edit: the latching power switch, of correct 4 pin type for AT cases, would be required if putting an AT supply into an ATX case, for an AT board, NOT required for ATX supply in ATX case with AT board.

Well, I have ordered at Ali a cheap AT 2 ATX Adapter cable, plz take a look at the picture and tell me your honest opinion, as I m not an electrician:

eliot_new wrote on 2026-01-22, 13:14:

BitWrangler wrote on 2026-01-19, 16:58:

Using an ATX supply on AT board... […]
Show full quote

Using an ATX supply on AT board...

First, the adapter, does it short power good to turn on ATX supply right away or does it have a 2 pin header? Or maybe a jumper? If it has a jumper or a 2 pin header you should be able to put ATX power switch to that header/jumper and turn on and off with the case switch.

If it doesn't, and is hardwired to turn on, use an ATX supply with a rear power switch or use a power bar with an off switch.

Latching switch will do you no good in this situation unless you have a qualified electrician make a mains power switching cable extension from the supply like the old AT supplies had.

Edit: the latching power switch, of correct 4 pin type for AT cases, would be required if putting an AT supply into an ATX case, for an AT board, NOT required for ATX supply in ATX case with AT board.

Well, I have ordered at Ali a cheap AT 2 ATX Adapter cable, plz take a look at the picture and tell me your honest opinion, as I m not an electrician:

It's not the best one but it works. Got one myself in a converted ATX case without problems. Cables to the switch were a bit short though.

eliot_new wrote on 2026-01-22, 13:14:

BitWrangler wrote on 2026-01-19, 16:58:

Using an ATX supply on AT board... […]
Show full quote

Using an ATX supply on AT board...

First, the adapter, does it short power good to turn on ATX supply right away or does it have a 2 pin header? Or maybe a jumper? If it has a jumper or a 2 pin header you should be able to put ATX power switch to that header/jumper and turn on and off with the case switch.

If it doesn't, and is hardwired to turn on, use an ATX supply with a rear power switch or use a power bar with an off switch.

Latching switch will do you no good in this situation unless you have a qualified electrician make a mains power switching cable extension from the supply like the old AT supplies had.

Edit: the latching power switch, of correct 4 pin type for AT cases, would be required if putting an AT supply into an ATX case, for an AT board, NOT required for ATX supply in ATX case with AT board.

Well, I have ordered at Ali a cheap AT 2 ATX Adapter cable, plz take a look at the picture and tell me your honest opinion, as I m not an electrician:

It looks like the power good wire and ground are left out there to go to a momentary switch as is normal on an ATX case... though you need to adapt the spade terminals to pins.

Edit: I have forgotten what the default on the T2P4 is, but some Asus boards seem to default to a soft power on by tapping the space bar when they notice they are on a "green" PSU (Not old standard AT) so that's just a note to hammer the space bar if you switch it or join the wires and nothing is happening.

Today I have bought a bi-stable switch from Hornbach. Here is a picture of my planned installation. What do you think? I have not soldered it yet.

👍👍👍
Kind of overkill but it will do.

You could also connect the ATX power button between +5VSB and a flip-flop that controls a transistor switching PS_ON to ground. Then you wouldn't need an extra power switch.

Here's an example of that solution: https://amigastore.eu/en/419-atx-to-at-power-adapter.html

The ATX power button connector goes into the header on the adapter board, and you can then use the ATX button as an AT toggle switch. No case modding needed.

Result: I simply wrapped the green and black cables with tape, thus short-circuiting them. Then I switched the ATX power supply from 0 to 1, and the board booted up. A positive start, a real success, hurray! But: unfortunately, the Dallas CMOS chip is empty. Therefore, I can't save any BIOS settings. Replacing it would cost me more than €30, including parts and professional installation. So, I'll probably return the board. A real shame. As a teenager, I dreamed of owning an Asus P55T2P4 one day. The takeaway is that I can at least install and get AT boards working.

There are ways of fixing the Dallas, all you really need is a CR2032 battery holder, soldering iron, and a triangular file or dremel with engraving tool for grinding away the plastic. This is a lot harder to do if the Dallas is soldered though.

Even NOS P55T2P4 boards will have a dead Dallas these days. It has become an essential part of the retro hobbyist toolset to deal with dallas chips now, either replacement or hacking for backpacking an external battery.

There's probably a market for a clamp on dallas re-power gizmo though which would use pointy screws to pierce and make connection.