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New power supply for Pentium MMX

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First post, by BraveToaster

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Hi,

I have an original Pentium 233 MMX from the 90s that I'm using as my main retro machine. So far I've replaced the IDE hard disk with a CF card (after one of the two already died anyway) and added an external battery to the Dallas RTC chip.

So far, so good. The only remaining project for me with that PC would be to replace the old power supply, assuming that the capacitors are probably not in great shape after all these years and it's fairly noisy anyway - which is particularly noticeable now that the drive noise is gone.
Obviously, a PC of that age does not have an ATX power supply, but an AT one.

Now, who has experience with renewing the power supply on a machine of that age? Is it as easy as taking a low-power ATX PSU (like this one for example) and an ATX-AT adapter (like this one) or is there more that I need to keep in mind? At the very least I need a few more adapters, like power for the floppy drive, CD-ROM, etc, right?
I noticed that most modern PCs have the PSU on the bottom while the old PC has it at the top - is that potentially an issue when mounting it?

But would the mainboard adapter "just work" or is there anything I'm not thinking about but should look out for?

Thanks!

Reply 2 of 7, by Pierre32

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Matth79 wrote on 2022-02-27, 23:22:

You might need an ATX-AT adapter with a -5V regulator - or a voltage blaster -5V card in a spare ISA slot

OP, here is some info on expansion cards that would need -5V: ISA Cards & Devices Requiring -5V

Otherwise yes, the AT-ATX adapter should Just Work.

Reply 3 of 7, by BraveToaster

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Thanks! I probably don't have an ISA card that needs -5V, since I only have a ALS100 sound card there. I'll try it with the simple cable and report back if I was successful. Might take a while until all parts arrived and I had time to try it out.

Reply 4 of 7, by Cuttoon

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the -5 issue is worth mentioning, if rarely relevant.

Other than that, sure, any random atx piece should do. Just don't expect some atx junker from the pile to be significantly more dependable than the original.
Only PSU that ever blew up on me, taking out a kt3-ultra and a gf4, was a five year old Enermax.

If you're getting a new one anyway and want to optimize, consider efficiency - usually best at 50 % load. And socket7 systems without too many things attached probably have some 50 Watts overall, so any contemporary one will be total overkill.

Very un-authentic but possibly elegant solution: One of those micro ATX or ITX PSUs with external DC. Like this, just a vague example:
https://www.ebay.com/itm/24Pin-DC-12V-160W-Pi … e-/133265542575

Yet, I have no practical experience with that. Just an idea that could save you some money and weight. Chances are, there's some 12 V plug already in your possession.

I like jumpers.

Reply 5 of 7, by Cuttoon

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btw, the PSU being at the top of the case since the dawn of time is probably due to the fact that their fan used to ventilate the whole case and warm air tends to go upwards - which does not matter any more in modern cases with half a gazillion extra fans.

I like jumpers.

Reply 7 of 7, by Cuttoon

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lawyerpepper wrote on 2022-02-28, 14:07:

Also an option, a new AT power supply

Dude, that is, like, seriously weirding me out.
Are those NOS or actually new? If so, is that even legal?!?

I mean, that's like someone printing old newspapers...

I like jumpers.

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