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Help with IBM XT Power Supply

G

gleegum

Member
Joined
Apr 7, 2016
Messages
49
Location
Uruguay
Hi all,
this is my first post in VCFED. I love to repair old stuff, although I don't know much about electronics I try to mess around with them until they work, or totally destroy them! I've got some Commodore and Amiga stuff, but never an IBM this old.

So I got this IBM XT with the 130w PSU for $15.
At first the whole computer was completely dead, then doing some research I found and replaced a bad tantalum cap on the +12v line, and attached another PSU from a working 486 I have and the computer booted.

After fixing the shorted cap on the motherboard, I attached the original PSU, and it worked for at least 7-10 seconds then it stopped. Trying to power it up again gave me nothing but a 'click' sound inside the PSU, I think this is a relay.
So I think something got damaged inside the PSU.

Are there common failures that I can look at inside the PSU? Inspecting visually doesn't gives me any clues. I replaced a cap that installed and with the multimeter set to continuity gave me a short, but after removal it was fine. I don't have a ESR tester.

I've tested the PSU conected to the motherboard, connected to an mfm drive, to a floppy drive, to some ide hdd, all the same result, the clicky sound.

Let's say I can't repair the PSU, is it ok to use the 486 AT as a replacement? Is it a better option than the original one?

Here are some more pics: https://goo.gl/photos/vgWRE1f2onvZmms16
TIA
IMG_3514.jpg IMG_3518.jpg IMG_3520.jpg IMG_3521.jpg IMG_3522.jpg IMG_3523.jpg IMG_3524.jpg
 
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framer said:
You can take the guts out of the new PS and put it in the XT PS case. Only you would know of the change.
Click to expand...

Yeah, I was thinking about this, so I can keep the red lever to turn the PC on/off.

Anyway, I'll keep the guts of the original PSU and will try to fix it someday.
Thanks!
 
When a power supply shuts down, it needs to be powered off for maybe 15 minutes so the mains cap discharge. Then it would probably fire up again. Am I seeing a crack in one of the rectangular green caps ?
 
retrogear said:
When a power supply shuts down, it needs to be powered off for maybe 15 minutes so the mains cap discharge. Then it would probably fire up again. Am I seeing a crack in one of the rectangular green caps ?
Click to expand...

I didn't know that, anyway I left the power supply disconnected for one day and it didn't work. I already transplanted the guts of a working AT PSU into the case of the XT supply. I don't have the original PSU here with me to check about that green crack, but I'll take a look. Now I'm waiting for my xt keyboard cable to arrive as the PC gives me a 301 error code. Thanks

Pic with the new PSU inside the old PSU case
https://goo.gl/photos/o9M4SwwaWmYQu1xc9
 
retrogear said:
When a power supply shuts down, it needs to be powered off for maybe 15 minutes so the mains cap discharge. Then it would probably fire up again.
Click to expand...
gleegum said:
I didn't know that,
Click to expand...
Different models of power supply are going to have different minimum-off-time requirement.
As examples, the following is from the Technical Reference documents of the IBM 5150/5160/5170:

IBM 5150: "Power On/Off Cycle: When the supply is turned off for a maximum (sic) of 5 seconds, and then turned on, the power good signal will be regenerated."

IBM 5160: "When the supply is switched off for a minimum of 1.0 second, and then switched on, the 'power good' signal will be regenerated."

IBM 5170: "When the supply is switched off for a minimum of 1 second and then switched on, the 'power-good' signal is generated, assuming there are no problems."
 
modem7 said:
Different models of power supply are going to have different minimum-off-time requirement.
As examples, the following is from the Technical Reference documents of the IBM 5150/5160/5170:

IBM 5150: "Power On/Off Cycle: When the supply is turned off for a maximum (sic) of 5 seconds, and then turned on, the power good signal will be regenerated."

IBM 5160: "When the supply is switched off for a minimum of 1.0 second, and then switched on, the 'power good' signal will be regenerated."

IBM 5170: "When the supply is switched off for a minimum of 1 second and then switched on, the 'power-good' signal is generated, assuming there are no problems."
Click to expand...

Thanks for the clarification!
 
Hi,

I have exactly this model of power supply, with exactly the same problem. If you ever work out what the issue was, please let me know.


In the meantime I had a third power supply and a spare AT one. So I took the advice here and put the insides of the AT into the shell of the case. I'm at the point where I'm about to connect the big flip switch but I'm not 100% sure on which wires should be connecting to where.

By my calculation I'm taking the Live coming from mains (male connection) and the Neutral coming from the mains and connecting each to the OFF side of the flip switch. I'm then going to attach the Neutral and the Live from the female monitor plug (which also connects to the main board), and connect them on the ON side of the switch, with Live opposite Live and Neutral opposite Neutral.

Is there anyone who could confirm that that sounds right? I've never done anything like this before and I'm a little nervous. (I can supply photos if it makes it clearer).

EDIT: Just to answer my own question - what I suggested above worked. I'm still interested in hearing about how to repair the power supply that just clicks as my other one does that too. Fan tries to spin for a fraction of a second then dull clicking sound.
 
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