Sounds like you have a dead short somewhere. I would be getting the power supply overhauled for starters. They have a couple of rifa's and aging capacitors.

Motherboards are pretty reliable, but suffer from oxidised ram sockets\bios sockets. I have seen a few tantalum caps go on them.. only if not powered on for a LONG time.

I turned it on one last time just now before opening it and it booted just fine. I'll still def check inside in case anything needs cleaning. Just for future reference, how exactly would I source replacement parts? When my Apple II PSU went bad, I was able to buy a new, prebuilt one. However, it looks like there isn't anything similar avaliable for the IBM.

Virtually every AT/ATX standard supply still floating around can power an IBM PC 5150, with a little bit of work. I believe some people designed small kits, and even adapted the red toggle switch that can run off newer guts. I think you might be able to use a PicoPSU (ATX) even. So if you can't find one that is in the exact IBM PC form factor, you certainly can get a PSU. Although there are likely some IBM PC form factor PSUs still around.

Note, if you have an original 5150 A with 4116 RAM, you need the -5V rail too. Please tell us your exact model.

Also note 2, that the 5150 can take a very long time, depending on how much RAM is fitted, compared to modern systems, to POST. You'll want to wait at least 2 minutes to make sure.

I don't know what you mean by the "screen doesn't turn on". How are you powering the display? What is the display type? Are you trying to say that there is no signal to the screen, but you are providing power to the screen?

More information on the situation will be helpful. You'll want to narrow down and identify the root cause of your problem, and explain everything you find.
https://minuszerodegrees.net/5150_5160/MDC/mi … diag_config.htm

Yes, having another power supply on hand can help in the diagnosis. You can use an ATX to AT adapter with a common ATX supply you have around.

SWZSSR wrote on 2025-02-11, 03:34:

Sounds like you have a dead short somewhere...

I'm not so sure about "dead short" - the fans run, which means there's 12v ... primary supply is 5v,
if that were shorted, the supply would likely completely shut down... most other minor rails probably
wouldn't stop POST ..

The fact that it's running again is a good sign (permanent damage much less likely).
Caps are always suspect in equipment this old... especially since you've already had one
fail. Chances are there are more degrading .. fortunately it's usually pretty easy to find
compatible caps for most PSUs.

There would have been a reason the cap that was removed (due to failure) was originally designed into
the machine ... (manufacturers don't like to waste money/assembly on superfluous parts), it's absence
may cause something else to run "out to spec"which can cause unreliability and/or degradation ... best
to replace it even if it seems to work-ok without it.

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal

It's always the capacitors. It's never not the capacitors. (until it isn't, but that's always a safe bet.)

DaveDDS wrote on 2025-02-11, 15:18:

I'm not so sure about "dead short" - the fans run, which means there's 12v ... primary supply is 5v,
if that were shorted, the supply would likely completely shut down... most other minor rails probably
wouldn't stop POST ..

I'm not so sure this hint applies to the original 5150 supply. Early variants had an AC fan directly connected to mains, so a running fan in this specific case might not indicate a running power supply. Your approach is valid for most supplies from the mid 80s or later, though.

mkarcher wrote on 2025-02-11, 17:27:

DaveDDS wrote on 2025-02-11, 15:18:

I'm not so sure about "dead short" - the fans run, which means there's 12v ...

I'm not so sure this hint applies to the original 5150 supply. Early variants had an AC ...

True, odd that I didn't remember that considering I had both a 5150 (PC) and a 5160 (XT)
(but that was "a couple" years ago!)

The spinning fan would at least indicate that no AC fuse had blown... If the supply had a "dead short"
I would have expected some noises/smells/smoke as internal components gave up the ghost.

And now that we know it "came back", we can be pretty sure that didn't happen.

I still would recommend recapping (or at least closely examining the caps in the PSU)
(Personally I'd pull them an measure their current actual capacitance - but not everyone
has the tools to do this)

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal