If you search ATX 1.2 then you can find a couple on eBay. I saw at least two. One from UK and one from US.
They seem like they are fair priced. Not too expensive, yet not cheap. Somewere in the middle of the road.

If you are are looking for ATX power supplies to power an AT board, then there is a converter with -5v generator.
This way, you can use a modern PSU without -5v rail.

http://www.ebay.com/itm/ATX-20-PIN-to-AT-P8-P … uFSqkmHj4SuUliA

Thanks for the quick reply
Unfortunately my PC is atx, I guess there isn't a 24 pin to 20 pin atx adapter with -5v generator?

What exactly do you need the -5V rail for? Cards that require it are actually not very common.

The cpu I think but tbh I don't know
It has a 2.0v slot 1 Pentium 3 600mhz, voodo2 sli, nvidia TNT, creative soundblaster live 5.1 and 256 mb ram on a Asus p2b
I've tried starting it with a corsair 430w PSU I got past post but it would freeze loading win 98 😒

But I have no probs when using some no name brand PSU with -5v

Jumo213 wrote:

The pcu I think but tbh I don't know It has a 2.0v slot 1 Pentium 3, voodo2 sli, nvidia TNT, creative soundblaster live 5.1 and […]
Show full quote

The pcu I think but tbh I don't know
It has a 2.0v slot 1 Pentium 3, voodo2 sli, nvidia TNT, creative soundblaster live 5.1 and 256 mb ram on a Asus p2b
I've tried starting it with a corsair 400w PSU I got past post but it would freeze loading win 98 :/

But I have no probs when using some no name brand PSU with -5v

Which Corsair PSU is it and what are the ratings on the side? Especially the current rating for 5v (not negative 5, just regular 5v) as well as the combined power rating for the 3.3v+5v rails.

A lot of newer PSUs have, say, only 16-18A on 5v, and very low combined 3.3v+5v ratings like say 80 watts which several modern PSUs have. Not good enough.

You very likely don't need -5v, and if you did need it, your machine would almost definitely not turn on at all. And a Pentium 3 is a bit new to need -5v anyway.

Jumo213 wrote:

Thanks for the quick reply
Unfortunately my PC is atx, I guess there isn't a 24 pin to 20 pin atx adapter with -5v generator?

I don't know if those converters excist. Yet since you got a P2B board, have you been into the BIOS in
order to see, if you can disable power monitoring of -5v?
On some SS7 boards, and in particulair the Asus P5A, you have that option.
Both the P2B and the P5A are from around the same timeperiod. So the option might be present.

It's possible to make such a converter, but your CPU will certainly not be using -5V dc. It's most frequently required for certain ISA sound cards in the retro world.

From the relevant thread:

QBiN wrote:

ISA Cards: […]
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ISA Cards:

• Creative Labs CT-192x - AWE32 Upgrade ISA Card (aka "Goldfinch") - Symptom: Low / No Audio
• Creative Labs CT-1350B (Rev 049151) - Sound Blaster 2.0 - Symptom: Low / No Audio
• Roland LAPC-I - LA Synthesizer + MPU-401 Card - Symptom: No Audio from LA Part
• Media Vision PAS16 - Pro Audio Spectrum 16 (650-0044 56B / FCC ID: IXW-PAS16NS) - Symptom: Incorrect Playback Speed / Timing Circuit Issues
• Media Vision JAZZ16 - Jazz 16 (650-0066-02 / FCC ID: IXW-JAZZ16) - Symptom: Incorrect Playback Speed / Timing Circuit Issues
• Media Vision Pro Audio Studio 16 - PAS Studio 16 (650-0052) - Symptom: Incorrect Playback Speed / Timing Circuit Issues
• 3Com EL16/TP - Etherlink 16 TP, 16bit NIC - Symptom: ??

ISA Cards & Devices Requiring -5V

Get an AT style PSU and buy an AT-ATX converter. Newegg still has AT power supplies still being manufactured. The Athena power brand has worked well in 486 build, and is rated @ 300W

It's trivial to add a -5V line to an ATX PSU. Just wire in a 7905, powered from the -12V rail. Can be done internal or external to the PSU.

dosgamer wrote:

It's trivial to add a -5V line to an ATX PSU. Just wire in a 7905, powered from the -12V rail. Can be done internal or external to the PSU.

or a MAX739 or similar inverting DC-DC converter that can run off of the 5v rail or 12v rail and provide -5v output (hence the "inverting")

Your idea is of simpler to implement but MAX739 is still simple.

Note that ATX PSUs often offered around 300mA on -5v, and at 300mA you'll be dissipating 2.1W with your method (7 volts drop * 300mA). TO-220 will have a junction-to-ambient rating of about 60C/W. Should add a little heatsink ideally, though if you're not actually pulling anywhere near 300mA, you'd be fine without. If you did pull 300mA, that would also use up around a third to half of your -12v rail current capacity, but you're probably not using much -12v either so that also should be fine.

Efficiency will be very low, like 40% or so, based on the voltages, but if you're wasting 60% of just a couple of watts, no big deal.

MAX739 avoids those problems for the most part, but again is not really necessary. Just rambling on my part. As usual.

A buck boost converter IC will invert polarity with high efficiency. It does require filter components as it's a switch mode converter.

The same seller has multiple variants. I have this one.

http://www.ebay.com/itm/NEW-6-ATX-24PIN-NEW-N … toAAOSweW5U7MKW

kenrouholo wrote:

Which Corsair PSU is it and what are the ratings on the side? Especially the current rating for 5v (not negative 5, just regular 5v) as well as the combined power rating for the 3.3v+5v rails.

A lot of newer PSUs have, say, only 16-18A on 5v, and very low combined 3.3v+5v ratings like say 80 watts which several modern PSUs have. Not good enough.

You very likely don't need -5v, and if you did need it, your machine would almost definitely not turn on at all. And a Pentium 3 is a bit new to need -5v anyway.

It is a 430w PSU as it turns out, 20A on both the +3.3v and +5v and 110w combined

What ratings do you think it will need to work?

brostenen wrote:

I don't know if those converters excist. Yet since you got a P2B board, have you been into the BIOS in order to see, if you can […]
Show full quote

I don't know if those converters excist. Yet since you got a P2B board, have you been into the BIOS in
order to see, if you can disable power monitoring of -5v?
On some SS7 boards, and in particulair the Asus P5A, you have that option.
Both the P2B and the P5A are from around the same timeperiod. So the option might be present.

Mmh no I'll have a look

You could just search for brands that were common to the early 2000s as many maintained the -5v rail like Enermax and Antec ect. Many of the favored units from that period also have the stronger +5 rail that is needed for so many pentium 3 and athlon xp era builds. If all else just buy one of those adapters.

dosgamer wrote:

It's trivial to add a -5V line to an ATX PSU. Just wire in a 7905, powered from the -12V rail. Can be done internal or external to the PSU.

Trivial is in the eye of the beholder. For an EE or an electronics hobbyist, sure. But let's not assume everyone putting together a retro PC has the knowledge to source, correctly solder, and implement a voltage regulator as an addition to their retro PC.

I think going down the path of finding a PSU with enough 5V+3.3V wattage would be the most fruitful for the average retro builder in this situation.

QBiN wrote:

Trivial is in the eye of the beholder. For an EE or an electronics hobbyist, sure. But let's not assume everyone putting together a retro PC has the knowledge to source, correctly solder, and implement a voltage regulator as an addition to their retro PC.

I dunno man. People into old electronics really ought to learn to solder, even if they only buy some cheapo "Aoyue" or "Yihua" or whatever other Wan Hung Lo brand of iron they can get for $20 or so. I don't really understand why people would refuse to learn life skills, but have no issue spending time online talking about lack of skills... I'm not talking about anyone specific here as this is just a hypothetical argument anyway.

Would you buy an old, beat up car if you didn't know or intend to learn how to fix up most of the issues? Some people do but it's a pricey and bad way to go.

Not saying that the voltage regulator solution for -5v rail is ideal for OP but I don't think it's a good excuse for anyone to say that they can't solder when we're on a forum about fixing up old electronics.

Jumo213 wrote:

It is a 430w PSU as it turns out, 20A on both the +3.3v and +5v and 110w combined

What ratings do you think it will need to work?

110 watts for those rails is low especially when you're doing something like V2SLI.

I'd say you should get something where that rating is more like 150 watts or higher.

You can easily find that rating being a bit higher on some supplies, like 130 watts on some models, but 20 more watts there is not much of an upgrade and may or may not solve your problem, so I don't recommend that. Double that difference with a 150w rating and you should be good to go.

And yes as someone else mentioned you can check out 2000s era supplies that still had -5v if you'd like to get a supply that has it just in case you do need it... try an Enermax Whisper series, perhaps an EG365P-VE which is fairly common on Ebay. Last model with the -5v rail as far as I know. For FSP you could go with a "60PLN" series like FSP350-60PLN. Not sure offhand of other model numbers of other manufacturers for supplies that still had -5v rails.