• Please review our updated Terms and Rules here

IBM 5150 troubleshooting

RC14

Member
Joined
Nov 25, 2019
Messages
20
Location
Northern California
I just picked up an IBM 5150 and it doesn't appear to power on (no "short beep" as described in the IBM Guide to Operations). How can I troubleshoot it? What should I look for when opening it up? I'm a novice to PC and PC Compatibles having stuck to Apple, so sorry about any dumb questions!
 
Minuszerodegrees will be an indispensable resource! The Minimum diagnostic configuration might be a good starting point in particular. As far as it totally playing dead on startup goes...If you've got a spinning fan and the PSU voltages check out that could indicate Bank 0, the soldered-down row of 4164 RAM chips on the motherboard, has a fault somewhere. The stock IBM BIOS REALLY doesn't like it if there's bad memory in the first 64k.
 
Can you tell if the power supply fan starts? If it has the full 640K of RAM, it will take about 40 seconds to finish POST before it will beep.
 
Just an update: I've tested out the minimum diagnostic configuration, and now I'm getting a short beep - and then smoke from the PSU. I don't really know what's going on, but I'll take a look at the inside of the power supply. Any thoughts? I get the beep after about 15 seconds and it's only when left running for a few minutes that I get the smoke.
 
Also, extra information: the monitor that came with the computer has a few pins broken off the connector, so I haven't been able to use it - I'm looking around for repair guides and also looking for replacements, but it's a CGA monitor (as far as I can tell from my little research) and I haven't found any yet. It does appear to have 640k of RAM (there's an AST card inside that had the number 64 on it, but I'd need to check up on that, as well as a 20mb hard drive and an external floppy card. The video card I am confused by, as it has (what I think) is a CGA port as well as a much longer port that I don't recognize.
 
The video card I am confused by, as it has (what I think) is a CGA port as well as a much longer port that I don't recognize.
Provide a photo of it.

and then smoke from the PSU. I don't really know what's going on, but I'll take a look at the inside of the power supply. Any thoughts? I get the beep after about 15 seconds and it's only when left running for a few minutes that I get the smoke.
A possibility:

The 5150's PSU contains a few line suppression capacitors. Sometimes, one ruptures, releasing smoke and odour.
This often confuses people, because the power supply continues to operate (i.e. the smoke means something in the PSU failed, but the PSU is still working).
See the 'Line Suppression Capacitor' section of [here].

Are you sure that the source of the smoke is the PSU, and not smoke sucked into the PSU ?

Just an update: I've tested out the minimum diagnostic configuration, and now I'm getting a short beep ... I get the beep after about 15 seconds ...
A short beep when in the minimum diagnostic configuration (MDC) ? In the MDC configuration, expected is a series of beeps, 1 long then 2 short.
 
A warning, from [here]:

Aged tantalum capacitors are known to explode. That has happened to me many times, particularly when I have acquired something that has not been powered on in years. If the motherboard, or expansion cards, are exposed to your face when you power them on, then consider wearing eye protection.
 
Also, extra information: the monitor that came with the computer has a few pins broken off the connector, so I haven't been able to use it
Broken off, or not present ?

For example:
* MDA does not use pins 3, 4, and 5. In the 9-pin connector of my IBM MDA monitor (IBM 5151), those pins are not present.
* CGA does not use pin 7. In the 9-pin connector on my IBM CGA monitor (IBM 5153), pin 7 is not present.
 
The 5150's PSU contains a few line suppression capacitors

Hmm, I don't see any - maybe it's a third party power supply?

Are you sure that the source of the smoke is the PSU, and not smoke sucked into the PSU ?

Yes, I'm quite sure - the smoke was coming straight out of the PSU vent.

A short beep when in the minimum diagnostic configuration (MDC) ? In the MDC configuration, expected is a series of beeps, 1 long then 2 short.

That's the other thing that I'm confused by - I assume that the faulty power supply caused it to perform oddly, but something on the motherboard could also be messed up.

Broken off, or not present ?

Ah, I'll have to take a look.
 
MDA does not use pins 3, 4, and 5. In the 9-pin connector of my IBM MDA monitor (IBM 5151), those pins are not present.

That's what it is - thank you!

I also figured I'd attach some photos of the PSU. I think the capacitors are leaking, but it may just be some sort of glue. Also, R19 appears to be cut, but intentionally (maybe as a switch for input voltages). Again, I don't see any line suppression capacitors, but that just may be me and my lack of experience. Nothing appears to be burnt, however, which I don't really understand it has at least smoked twice, and gave out enough smoke for me to notice. Thank you so much for your help! IMG_4398.jpgIMG_7198.jpgIMG_8904.jpg
 
IT WORKS! I don't know what I was thinking, but I decided to power it on again. Maybe it was dusty in the PSU and I dispelled it? I don't really know, but it isn't smoking anymore and I was able to start putting cards back in.
 
I also figured I'd attach some photos of the PSU. I think the capacitors are leaking, but it may just be some sort of glue.
Yes, under the large and medium sized aluminium electrolytic capacitors is glue.

Hmm, I don't see any - maybe it's a third party power supply?
Again, I don't see any line suppression capacitors, but that just may be me and my lack of experience.
Line suppression capacitors are supplied in various forms. In your PSU, some of the brown/blue capacitors may be performing the function.

IT WORKS!
Congratulations.
 
Back
Top