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5150 PSU. UK Repair possible?

U

UKRetro

New Member
Joined
Apr 30, 2010
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9
Hi

I've recently collected a November 1984 IBM 5150 with Floppy, HDD, CGA & colour monitor but it won't power up.

I've removed each of the cards in turn and after removing the serial/parallel controller, the HDD span up but I didn't have the CGA card in to see what was happening onscreen. On replacing the graphics card, the machine refused to spin up again. I've since removed all the cards apart from the graphics card and disconnected the power connectors from the Floppy/HDD but I still get nothing.

The 5150 has apparently sat unused for over 2 years in a kitchen and was sold as working.

Tonight, I thought I'd check the voltages on the PSU and the most it outputs is 0.039v!

I'm glad it looks like a PSU fault - I should be able to get this repaired.

I'm not qualified to go poking around inside 240v mains powered PSUs, so wanted to ask if anyone knew someone or somewhere in the UK qualified to repair mine?

Regards
Mark
 
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Have you cleaned it up before you first used it? Cleaning is also a good opportunity to check if theres any damage (like leaking batteries etc)
Atleast you know the PSU is defective, but that doesn't mean there's nothing else wrong with it.
I read in another topic here those IBM's are capable of using a standard PSU, but I'd say better wait with testing it with a standard AT PSU until someone with more knowledge of IBM's posts here ;)
 
There is a fuse inside the PSU soldered to the bottom board. You will have to open the PSU to check it. Unplugged! Check it with an ohmmeter for continuity. If it isn't the fuse, it will be cheaper to buy a replacement off of eBay than to pay the labor cost at a repair shop.
 
UKRetro said:
Tonight, I thought I'd check the voltages on the PSU and the most it outputs is 0.039v!
Click to expand...
Just because one measures incorrect voltages from the power supply does not mean that the power supply is faulty.

Example 1: Most power supplies for PCs require some form of a load in order to start/operate. If the measurement was done with nothing connected to the power supply, the power supply probably would not have started. In my experience, the motherboard itself is enough of a load, and the hard drive itself is enough of a load.

Example 2: A complete or partial short circuit on the motherboard may be causing the power supply not to start.


Since it is unlikely that both the motherboard and the hard drive are faulty, try this experiment:
1. See if the power supply works when it is only connected to the hard drive.
2. See if the power supply works when it is only connected to the motherboard (no cards fitted).

If in BOTH cases, the power supply doesn't work, then I would take that as 'faulty power supply'.

If in BOTH cases, the power supply works (+5V/-5V/+12V/-12V present and POWER GOOD line at +5V), then there must be a short in the CGA card (and potentially other cards).

If in one case the power supply works and in the other case not, that would indicate a short in the device that was connected in the case where the power supply didn't work.

Let us know how you go.
 
k2x4b524[ said:
5150 with an internal hard-drive? What is the Wattage of the PSU, if it's 63.5, then it's not going to handle the hard drive.
Click to expand...
The PSU is 130W and (I'm told) was fitted by an IBM engineer as an upgrade when the HDD was fitted..

I still need to find time to carry out the voltage on load test.

Any ideas where would I can look (other than eBay) to find a replacement PSU, bearing in mind, I'm in the UK? (240v)

Regards
Mark
 
IF YOU READ THE ORIGINAL POST!!!! *
Hdd spins up when the graphics card is out, but stops when it's in - Tantalum power rail decouplers shorted on the graphics card?

At the very least check the graphics card power rails for shorts, and I'd look at the 3 terminal capacitor on the 12V line first (orange/yellow blob), I've had a couple of them go.



*slight hangover :-(
 
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nige the hippy said:
IF YOU READ THE ORIGINAL POST!!!! *
Hdd spins up when the graphics card is out, but stops when it's in - Tantalum power rail decouplers shorted on the graphics card? (
Click to expand...
Quite likely. Covered by the following in my post:
"If in BOTH cases, the power supply works (+5V/-5V/+12V/-12V present and POWER GOOD line at +5V), then there must be a short in the CGA card (and potentially other cards)."
 
Sorry for shouting, I was trawling through the rest of the posts (that were missing the obvious) with a headache:oops:
 
Hi

I've now had the PSU apart and checked the fuse. It's still intact. I assumed so as the fan spins but wanted to check first, just to be sure.

Whilst I was in there, I blew out all the dust and cobwebs with my airbrush compressor (with a moisture trap fitted) and refitted the PSU.

I tested it this morning by plugging in just the HDD (without connecting the PSU to the motherboard) and powering up. Still nothing. And still negligible voltage(s) on any rail.

As mentioned in today's earlier post, this is a 130W, retro-fitted PSU which was put in the PC on the day the HDD was fitted.

I think perhaps my original post mislead some of you.

The HDD didn't (and still doesn't) spin up with the graphics card removed, I started my diagnostics by removing each card in turn, trying to power-up after each card was removed.

From a (more modern) PC building and troubleshooting background, I've always tried removing cards one-by-one from a misfiring PC, in an attempt to rule out IRQ and I/O clashes, bad chips, etc.

On the day I brought the PC home, I started removing them from left to right.

The graphics card was first (Always a prime suspect on later PCs) and powered up. Nothing.

Then I removed the RAM expansion card too. Still nothing.

On removal of the Serial/Parallel I/O card the HDD span up!

Ah, I thought. I found you...

Back in went the RAM & GFX card (leaving the I/O card out) and...

Nothing. And never since.

The unit didn't power up at all when I got it home. It only attempted to spin up the HDD ONCE, on removal of the I/O card but has never done so since.

I still suspect the PSU is at fault. Apparently, the PC sat unused for 2 years before I collected it.

I think the HDD spinning up was just coincidental with removal of the I/O card. By this time, only the floppy and hard disk controller cards were still in the machine. The Colour Graphics, RAM and I/O cards were on the bench at this point).

Would anyone know where I could find a replacement 130W (UK) PSU for this unit?

Regards
Mark
 
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It probably is the PSU, but it seems odd that the HD span up that one time. It could be that the HD alone doesn't provide enough load for the PSU to start. If you return the system to the same configuration as the time the HD span up, is it still dead? In that case, I'd say get a new PSU. Otherwise it's possible that both the CGA card and the serial/parallel card are faulty (e.g. a short). For the two minutes it'd take to check, it's worth trying. Would be a shame to source and fit a new PSU if the cards were the cause all along...
 
My best guess would be either Ebay, find a similar defective unit (not likely) and use that PSU or try to find out if a standard AT PSU would be able to power it up. I don't know if it's possible to fit standard AT PSU's and if so, which models are compatible and which are not.

You could try spinning the harddrive up with another PSU, then atleast you'll know that the harddrive isn't completely dead.

cosam said:
It probably is the PSU, but it seems odd that the HD span up that one time. It could be that the HD alone doesn't provide enough load for the PSU to start. If you return the system to the same configuration as the time the HD span up, is it still dead? In that case, I'd say get a new PSU. Otherwise it's possible that both the CGA card and the serial/parallel card are faulty (e.g. a short). For the two minutes it'd take to check, it's worth trying. Would be a shame to source and fit a new PSU if the cards were the cause all along...
Click to expand...
Still wouldn't hurt to have a spare part kicking around ;)
 
ok chaps, now the hangover's gone, the brain is working, this is how I'd tackle it.

Try the HDD with another psu (if you have one), at least you have a known good load.
99 times out of 100 (In my experience) an HDD is sufficient load to start a psu, so try the original psu out on the hard disk alone.
if that works, add the motherboard & try again.
Then try the cards one at a time, there could be multiple faults.
If it does turn out to be a faulty PSU, are you near Luton? I've become quite good at switchers in recent years, and my workshop's coming together too!
 
nige the hippy said:
ok chaps, now the hangover's gone, the brain is working, this is how I'd tackle it.

Try the HDD with another psu (if you have one), at least you have a known good load.
99 times out of 100 (In my experience) an HDD is sufficient load to start a psu, so try the original psu out on the hard disk alone.
if that works, add the motherboard & try again.
Then try the cards one at a time, there could be multiple faults.
If it does turn out to be a faulty PSU, are you near Luton? I've become quite good at switchers in recent years, and my workshop's coming together too!
Click to expand...
Hi

I don't have another AT PSU. I do have a more modern, working PC with an ATX PSU and the same type of power connectors. I take it the voltages are the same (nothing changed in 25 years?) and I'm not going to blow up my newer PC or burnout the 5150's HDD trying?

I've tried in the 5150 with just the HDD connected and the motherboard disconnected and it still doesn't spin up the HDD.

I'm nowhere near Luton (Bolton, in Greater Manchester) but I'd be willing to post the PSU if you could test it or try it in another 5150...

Thanks for the offer though! :D

Regards
Mark
 
Modern ATX PSU's don't have the -5V line anymore, so even if the PSU plug fits the motherboard, theres a good chance it will not work. You'll need an older generation which still supports both -5V and -12V.

If you only have 1 main computer, I wouldn't recommend testing the faulty(?) harddrive with it. If it breaks your only PSU you may find yourself without a working computer (the horror.....)
 
Actually the easiest way to check a psu is to use a psu test adapter. Such adapter could be purchased a Radio Shack for about USD 12.00. I was told that such adapter could determine a psu is faulty or not at the rate of 95%. I think what it does is to put a load on the heaviest wattage line, I just check the haviest wattage line means the +5 volt line and the ampere is at lease 25 A. I f the attached green LED lights up, the psu should be free of faults. If the psu is faulty, I do agree that it is better to buy an use one than have it repaired. These PC psu is no ordinary power supply, they are switching power supply which is very electronics involved.

Doug
 
Tetrium said:
Modern ATX PSU's don't have the -5V line anymore, so even if the PSU plug fits the motherboard, theres a good chance it will not work. You'll need an older generation which still supports both -5V and -12V.
Click to expand...

One can always insert a series-pass voltage regulator, such as a 7905 in the -12 lead to provide -5 if needed. The current used by an older PC is generally less than 1 ma on the -5 (used for substrate bias on 4116 DRAMs on the 16-64K 5150. If you have the 64K-256K lateer version of the 5150, the -5 isn't needed, unless you have some early DRAM cards requiring it).
 
UKRetro said:
Hi

I don't have another AT PSU. I do have a more modern, working PC with an ATX PSU and the same type of power connectors
Click to expand...

Just plug the HDDs power connector onto your modern PC (disconnect the old pc's mains lead & the hdds control & data cables first, just in case) it's still 5 & 12V. (obviously there's a slight risk to the modern machine, so don't hold me responsible if it does go bang!)

I've about 3 little jobs for people outstanding, but could get round to doing a PSU-by-post in a couple of weeks.
 
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