I have done similar thing with success several times, most of my AT towers have converted ATX supplies in it. If -5V is missing I use a 7905 on -12V like normally done in most power supplies with -5V or what Voltage Blaster does.
You often need to put a dummy load on the 3.3V line, many PSUs don't like unloaded 3.3V. Also there's often a remote sense line going to the ATX power connector, this one has to connect to 3.3V line in the PSU when you get rid of the cable.

One big issue is power, which I sidestep by putting ATX supply inners into AT supply one, and reusing the power switching capability, and permanently shorting PS-ON to ground. Alternatively you can switch the PS-ON signal with the front power switch but I prefer the PSU to get totally cut off so there's no wasted power happening from the stanby supply that will keep running otherwise.

informatyk wrote on 2024-08-23, 16:35:

Now I need to buy a decent ATX power supply, then I will cut off the 20-pin ATX connector and install P8 and P9 connectors. Green and ground will be connected to a regular AT switch. I know that such a power supply should have -5v, which is hard to find in newer models.
What do you guys think of this power supply?

Better off short ATX power-on (green wire) to ground in the PSU and connect 230 V (or 110 V) switch with cable for mains (as in the real AT PSUs). If needed get -5 V from PSU's -12 V line through some suitable voltage regulator.

I simply cut the wires from the ATX connector.

I then made the connectors for the AT power switch from the green ATX wire and ground. I chose this way because I just don't like the idea of 230 volts running inside my case to the switch.

Crimping the connectors was more difficult than I thought. I ended up doing it with pliers and unfortunately it's not perfect, but it shouldn't break. If you would also like to do something like this, I recommend buying a professional tool for this purpose.

I connected it to the motherboard and power supply and.... nothing happened except a super short little fan movement. I'm sure the power supply needs something on the 3.3v line, because I tested it first by shorting the green to ground and it was the same. Then I connected it to a normal motherboard and it worked. I will probably put a small LED or resistor there.

Personally I prefer off the shelf solutions that cost almost nothing.

ATX to AT affaires are dirt cheap

Also the data to molex connectors are cheaper than coffee.

Not that I'm afraid of the soldering iron, but it saves me the work.

For power cutoff, most modern power supplies have a dedicated switch on the back.

For three -5v you can easily solder an ic between the leads on the at-atx cable. If you need it, I mostly dont.

@waterbeesje:I already have this converter, but I want it to look more in line with the era and I have baby AT case. There is not much room for cables.
I already have -5v in my Fortron power supply. It's an old model.

waterbeesje wrote on 2024-08-29, 20:16:

Personally I prefer off the shelf solutions that cost almost nothing. […]
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Personally I prefer off the shelf solutions that cost almost nothing.

ATX to AT affaires are dirt cheap

The attachment Sff1060f17f4546d9af0e1c9175e4716ft.jpg_640x640Q90.jpg_.webp is no longer available

Also the data to molex connectors are cheaper than coffee.

The attachment Scc6e161021fb4bf29c4fae57bbd077cak.png_640x640.png_.webp is no longer available

Not that I'm afraid of the soldering iron, but it saves me the work.

For power cutoff, most modern power supplies have a dedicated switch on the back.

For three -5v you can easily solder an ic between the leads on the at-atx cable. If you need it, I mostly dont.

Sata to Molex adaptors give me the creeps, heard and seen too many things go wrong with the things. Im sure there are far better ways to make these nightmare adaptors so they dont cause shorts from the molex pins working their way loose.

informatyk wrote on 2024-08-29, 19:34:

Crimping the connectors was more difficult than I thought. I ended up doing it with pliers and unfortunately it's not perfect, but it shouldn't break. If you would also like to do something like this, I recommend buying a professional tool for this purpose.

Ditto, without the right tool it's a bit of an art to get the proper crimp on the conductor and one on the insulation for integrity.

informatyk wrote on 2024-08-29, 19:34:

I connected it to the motherboard and power supply and.... nothing happened except a super short little fan movement. I'm sure the power supply needs something on the 3.3v line, because I tested it first by shorting the green to ground and it was the same. Then I connected it to a normal motherboard and it worked. I will probably put a small LED or resistor there.

Looking at pictures... Did you maybe leave the power good signal hanging on the ATX connector? That should be moved over to the AT P8 at position 1, I think.

Trashbytes wrote on 2024-08-30, 11:48:

Sata to Molex adaptors give me the creeps, heard and seen too many things go wrong with the things. Im sure there are far better ways to make these nightmare adaptors so they dont cause shorts from the molex pins working their way loose.

+1, those are a fire waiting to happen. In particular with modern units where the 12V line can put out A LOT of amps before the protections kick in.

Many Bothans wrote on 2024-08-30, 14:24:

Ditto, without the right tool it's a bit of an art to get the proper crimp on the conductor and one on the insulation for integrity.

You just need small pliers.

I figured it out. I printed out a sheet of pinout AT, ATX, but I only have a black and white laser printer. The white connectors fused with the white sheet and I didn't notice that I made the P8 and P9 connectors, but rotated 180 degrees.

Fortunately, this did not fry the motherboard and it works, it boots. Now I'll get down to desoldering the unnecessary cables.

I finished this project. Unnecessary wires were cut (too much trouble to desolder), it's super quiet and solid.
It looks in line with the era, and unlike the ATX to AT converter, it does not take up space in small enclosures.