PSU suggestions for a retro gaming PC

[Toriessian]

I'm looking at building a couple retro PCs. Prolly something P-II/P-III based to be "reliable" and then a SS7 platform to play with. Get my quake on on a Cyrix MII and stuff
Any suggestions on power supplies? I figure theres prolly some ATX -> AT adapters out there. Not sure how reliable those are.

What PSU's are retro PC builders here using? I'd love it if I could throw in something newer for a power supply.

 

[GiGaBiTe]

By the time Super 7 and SECC2 PII/PIII motherboards came around, most everything was ATX. I've rarely ever seen anything beyond a Socket 5/7 board still use AT power connectors. Sometimes you'd see both if a manufacturer wanted to offer backwards compatibility, not not just AT on later board designs.

The problem you're going to have is that those old systems drew almost all of their power from the 5v rail, unlike the shift in the mid 2000s to the 12v rail and today where almost nothing uses the 5v rail. Supplies back then were geared to output 20, 30, 40 and sometimes 50A on the 5v rail. Modern ATX supplies are no no way designed or capable of delivering that much power on the 5v rail and will shut off or have erratic behavior. So if you have a fully decked out system with power hungry CPU, lots of cards and drives, you'll need to get a period correct supply. If you don't plan on fully decking out your rose tinted retro man box, you can try and dig around on the usual retailers for a PSU with the highest 5v rail rating you can find. You want one with at least 20A on the 5v rail.

Finding a vintage power supply is one thing, having it work is an entirely different matter. That era was on the leading edge of the capacitor plague, where shitty caps started showing up in computer parts, including power supplies. I've recapped and otherwise repaired hundreds of power supplies from that era because of failed capacitors. If caught early, you can get lucky and just do a full recap and be fine. If you catch it too late, then be prepared for extensive surgery on the unit, assuming it hasn't turned into a charcoal briquette.

One final BIG gotcha is that you need a supply with a -5v rail. The -5v rail is a legacy from the original IBM PC 5150 and was kept around for backwards compatibility reasons on the ISA bus. So even though that 99.9% of cards don't use this rail, many motherboards check for the presence of this rail and won't power on if it's not present. This rail was removed from the ATX specification in 2003-2004, so you'll need to get a power supply made before that time frame, or do some modification to make your own -5v rail. It's not terribly difficult to do with an LM7905 negative voltage regulator hanging off the -12v rail since the current requirement is virtually nothing.

The only power supply I can recommend from the era (because I'm the most familiar with) is the Antec SL series like the SL300, 350 or 400, but they definitely suffer from the capacitor plague and any unit you buy will be guaranteed to have bad caps and need to be recapped.

 

[Toriessian]

Thank you. That is the exactly the kind of answer I needed. I went to ebay and I see what you're saying. The +5 V rail on the SL400 is rated 38A and I looked at a slightly later era 650W PSU and I saw it only had 25A on the +5V.
Since this project is also about me learning how to solder, recapping a couple "working" SL400's looks like a good project to start with too!

 

[GiGaBiTe]

When recapping the power supply, make sure you get ALL of them. This is especially true of the small bastards buried under and behind things in hard to reach places, because the small ones going bad can cause the whole supply to not work if they go bad. They're usually in monitoring circuitry or startup circuits and are equally as important as the big ones.

I'd recommend a desoldering gun for this, because removing daughterboards and mosfets with a spring loaded solder sucker or wick will try the patience of a saint. And the spring loaded solder suckers have a habit of ripping pads off of the board, especially if they've been baked by heat.