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Found an Old IBM

Using my XT/286 at the weekend, there was a puff of smoke from the PSU and it shut down. Now it has exactly the same symptoms as your XT PSU - the fan moves slightly when switched on, but nothing works.

Open it up and see if any components show obvious signs of damage.
 
Using my XT/286 at the weekend, there was a puff of smoke from the PSU and it shut down. Now it has exactly the same symptoms as your XT PSU - the fan moves slightly when switched on, but nothing works.

Open it up and see if any components show obvious signs of damage.

Good to know.
I have a working vintage PSU on the way. I'll try to get a star screwdriver and fix this one (and have it as a backup).
 
Good to know.
I have a working vintage PSU on the way. I'll try to get a star screwdriver and fix this one (and have it as a backup).

Sorta obvious but please be very careful when playing with capacitors. If you want to discharge them before working you can take a screwdriver (with a non-metal handle) and short the two legs on the capacitors to discharge any left over voltage stored in them. This also if you haven't done it before can make a loud pop when it happens so fair warning depending on the power supply it can startle ya.

Goodluck though! The great part about vintage computers is they are often repairable and the parts are easy enough to actually desolder and replace if need-be.

- John
 
Goodluck though! The great part about vintage computers is they are often repairable and the parts are easy enough to actually desolder and replace if need-be.

- John

That's very true. In the last year, I've learnt that they are indeed fixable, and whereas prior to this collecting hobby I would be loath to touch anything inside the machine, I now have enough confidence (probably misplaced :) ) to get in there and get down and dirty with the hardware.

However, they may be repairable but then again, the components aren't necessarily easily REPLACEABLE They can be hard to find, so take care. Mind you, if it's not working anyway, what have you got to lose?

Tez
 
Okay looks like it's a bad PSU. I'd rather it be the PSU than the main board.
Rather than using a dummy load, I used a volt meter. I put it across a +5V and a ground, flipped the PSU on. The voltage is 5V for about a third of a second then it decays over 10-15 seconds to the point where it's mV. The fan only runs for the first 1/2 second also.

you can grab any spare AT PSU and hook it up to the machine. it's not going to fit in as a screw-in replacement, but you can see if the machine works. if it doesn't, and you know the AT PSU is cool by trying it on another machine, then you've got motherboard issues.


good luck, and let us know what happens!
 
you can grab any spare AT PSU and hook it up to the machine. it's not going to fit in as a screw-in replacement, but you can see if the machine works. if it doesn't, and you know the AT PSU is cool by trying it on another machine, then you've got motherboard issues.

I just got my spare XT PSU, it does the same thing.... Though I accidentally plugged it in with the switch on. So with these two PSU not working I haven't ruled anything out.

I have a few modern day power supplys but the motherboard power connectors are not compatible with the IBM.
 
Well my ATX PSU have 20 or 24 pin power connectors while the IBM needs two 6 pin power connectors. Way different; I doubt there's an adapter.

it's possible to make an adapter, but you'll have to bridge two pins also since ATX PSU's power on is controlled by the motherboard rather than an external switch. i've never tried it, but it should be possible. you don't have any AT PSU's from like a 286-486 or an early pentium?
 
You shouldn't use an ATX PS for several reasons. A Full AT or Baby AT are the only ones functionally correct other than a PC/XT unit.

Since both your PS's are apparently doing the same thing I would bet a dollar (ours, since it's only worth 60 US cents now :mrgreen:) that you have a shorted tantalum cap on either the motherboard or a plugged-in card.
 
Since both your PS's are apparently doing the same thing I would bet a dollar (ours, since it's only worth 60 US cents now :mrgreen:) that you have a shorted tantalum cap on either the motherboard or a plugged-in card.

I was thinking down that path until I did more troubleshooting.

Here's my latest method. I didn't trust using a HD as a load, so I got a real dummy load (meant for RF applications). I hooked up a voltage pin and ground pin to the load and monitored the voltage over the load via a volt meter.

I tested the +12,-12,+5, and -5 voltages and they are all near or at 0mV with the supply on. Yes, they started out with some voltage but quickly decayed.

So was this method correct and does it completely show that the PSU is bad?
PSUtest.jpg


I made sure the load didn't exceed the max output amperage of the tested pins.
 
Your dummy load is the wrong sort of "dummy load." That RF load is most likely 50 (or 75) ohms so will only draw 20mA per volt potential at best.

That's only 100 mA on 5V, 240mA on 12V.

The small hard disk will draw about 2 or 3 amps on the 5V and 1 amp on the 12V which is a light load but sufficient for a test. And, just as important, it loads both the +5 and +12 at the same time.

Since you have two apparently dead PC/XT PS's, why not take one apart and work on that? I'm interested in replacing the PS caps on both my PC's so this might help me too.
 
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I finally got the PSU open. Everything but the flyback transformer looks good(it looks as though it leaked a long time ago). From what I've read it supports the monochrome monitor. I just ordered a full schematic booklet on the 5160, so I'll try to see if this component can fail the whole power supply.
 
There is nothing to leak OUT of it. Melted, maybe, if there is an interwinding short.

I hate to rain on your parade, but, if that is the case, I'd be looking for a new PSU. Chances of finding a flyback that old (or even a substitute one) start at slim and go down from there.
 
I think you are referring to a transformer in the PS ... and it has nothing to do with whatever is plugged into the PS - that's just a power outlet taken from the power-in, perhaps switched, I don't recall.

I can't imagine how the transformer would "leak," it's probably just glue residue.

Have you removed the PCB and looked very carefully at the large caps for swelling and/or leakage? Use an ohm meter to check the small ones for dead shorts.
 
Yeah, often large and/or heavy components like transformers, caps etc. have support added with silicone or similar glue.

Watch out for nasty voltages when poking around there, especially if plugged in & on!

And try it with a disk drive or two for a load, just in case you're goin' down the wrong road...

mike
 
That's why I'm not an electrical engineer... hehe

The load you're using in the picture is intended to jack into a radio, etc. in place of the antenna, for testing/adjusting the RF output. There is another kind used for loading electrical equipment. (A similar term refers to me when I'm fitshaced...loaded dummy).

--T
 
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