Replace AT Power Supply \ VOGONS

Replace AT Power Supply

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First post, by topaz75

Posted on 2019-03-12, 20:33

topaz75 Offline

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Hi there,

just running into an issue that i haven't done before. I need to replace the AT power supply in my 486. It is connected to a switch on the case that is press fitted or plastic welded into the case, so wont come out. On the other end, it is soldered onto the PCB of the old, defective power supply.

Just wondering if there is a state of the art way to do this. I am taking the power supply out of an old COMPAQ DESKPRO. It would have its own case switch, but i don't think that would fit. So i have to cut it off and then fix that somehow. Do i have to desolder from the PCB in the power supply and reconnect there on the good one? Can I just connect the wires of the switch to the wires from the power supply with wire nuts? Should i keep the wire nuts/ connections within the power supply or is it fine to just have the spliced wires inside the case?

I realize all these approaches will work, just trying to figure out if there is a "right" way to do this.

Topaz

Reply 1 of 4, by retardware

Posted on 2019-03-12, 20:47

retardware Offline

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Never never use wire nuts on line potential together with low-voltage stuff that is intended to be touched by people.
Just splicing and covering with insulation tape would be even more no-go.
Electrocution risk.

The correct approach is to take measurements so you can solder off the switch connection from the new PSU, so you know how to correctly solder these into the old PSU/case.

Reply 2 of 4, by gdjacobs

Posted on 2019-03-13, 03:05

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Does the switch side have four wires (as is standard for AT)?

All hail the Great Capacitor Brand Finder

Reply 3 of 4, by SirNickity

Posted on 2019-03-13, 17:50

SirNickity Offline

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Yeah ... usually the switch has either four spade terminals (which simply slip right off, if attached to a tow strap and yanked by a suitably brawny tractor), or it might have four solder eyelets that are covered in heat-shrink or a plastic cover of some sort. The best way to replace the PSU is to remove the wires at the switch, and replace with the new PSU's cable.

Failing that, I would replace at the PCB. I don't like splicing mains wiring if I can avoid it.

Reply 4 of 4, by topaz75

Posted on 2019-03-18, 19:14

topaz75 Offline

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I kind of did it like that, in the end.

The damaged PSU had the spade terminals, so it came off relatively easy, but the new one had a switch soldered onto the cable. So I removed that, added some new spade terminals, encased them in heat shrink like the old ones had been and connected to old switch. Works beautifully.

And I can see how ATX power supplies were really a big improvement in that regard.

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