AT power supply help

[BigTroll]

Ok i'll make this short request long, back in year 2000 or so I was a 8th grader I was attempting to replace a AT power supply in a computer, when I hit the switch sparks shot out the back and the lights dimmed in the house. Ever since I have never touched a AT power supply and recently got a AT case with a bad supply.

I really want to build this computer but still scared i might fuck it up even though its only 4 wires. So my questions are as follows.

1. Once said AT power supply is hooked up, can I power it on without it being connected to the motherboard so I don't fry it?

2. I'll provide some pics of the rocker switch its not a push switch so you guys can hopefully let me know if its hooked it right. the rocker switch already has the color markings labeled from a previous person.

Pics to follow shortly.

[stj]

Re: AT power supply help

the sparks are possible with any supply - i'v had it with a couple of high end atx ones - it's just the MOV's failing that normally suppress mains spikes.
i wont deny that it's impressive to see it happen - specially if your next to the fan grill!!

if you want to test the supply without a board you should still connect a load - i used to use a couple of old harddrives for the task.

[Topcat]

Re: AT power supply help

AT PSU = Wires carrying line voltage to a mechanical power switch in the front of the case....unlike an ATX where all high voltage is safely contained inside the PSU housing. I've seen quite a few instances where sharp edges of the case snagged the line, or someone inadvertently poked around the switch with a screwdriver....either instance causing some fireworks, dimming lights, and even some snapped breakers in the load center.... You just have to use a little more caution with older AT stuff.

If you're wiring the switch, I believe they're color coded how they wire to the DPST switch...I don't remember it off the top of my head, but I can sure find out. If nothing else, just disassemble the power supply and trace the wires.

[stj]

Re: AT power supply help

switch wiring is usually on the psu sticker

[eccerr0r]

Re: AT power supply help

The classic original IBM AT / XT PSU that are oriented on the table, the power switch is built into the PSU along the side, so when it's mounted in the rear/right of the case, the big toggle switch is right there too. When the case is rotated to a tower, the switch is on top.

However some clone manufacturers relocated the switch, use a front panel switch, etc. and had to pass the 120VAC to the front, and that's where you may run into issues if you're not careful with the line power.

[BigTroll]

Re: AT power supply help

Okay I got the power supply, someone already labeled my rocker switch for me and it looks to be wrong from the label of the power supply as brown and blue shouldn't be on one side, from the label it looks to be brown and black and blue and white on one side.

I will wait for your guys response before I plug it in, I don't want a repeat of 20 years ago.

[BigTroll]

Re: AT power supply help

another thing I wanted to point out. when you search google for "AT power supply wiring" the first hit is some toms hardware article from 2001 and the guys is totally wrong https://forums.tomshardware.com/thre...switch.323966/ according to my label his wiring advice is wrong or Iam reading my label wrong, but whomever wrote the colors on my switch seemed to follow that guys advice.

[R_J]

Re: AT power supply help

The switch wiring looks correct, Black (line) White (Neutral) should come from the a/c input, Brown (line) and Blue (Neutral) feed the input to the power supply
With the switch off (or disconnected) and the power supply plugged in you should have 120vac across the black and white wires
Or check the resistance between the A/C inlet and the black and white wires. The only way to get it wrong would be to have the black and white wires on the switch so when the switch turns on it shorts out the a/c line

[BigTroll]

Re: AT power supply help

Thanks for the help, i'll start putting the supply and in switch into the computer.

[stj]

Re: AT power supply help

nice board - i have one like that for testing stuff.

one bit of advice, replace the fuse with a ceramic one - if that glass one blows it will make one hell of a mess.

[BigTroll]

Re: AT power supply help

Good news, I hooked it up like in the pictures i posted and it powered right up in the computer! so I can cross installing a AT power supply off my bucket list. I'll keep the fuse thing in mind also thanks for all the help everyone

[momaka]

Re: AT power supply help

one bit of advice, replace the fuse with a ceramic one - if that glass one blows it will make one hell of a mess.

Or just sleeve it with heatshrink.

I also advise you always test AT PSUs with a good load - especially on the 5V rail. Some AT PSUs won't like it or work properly without at least 1 Amp of load on there. So you may need a few incandescent (or halogen, I suppose) 5-12V bulbs.

The classic original IBM AT / XT PSU that are oriented on the table, the power switch is built into the PSU along the side, so when it's mounted in the rear/right of the case, the big toggle switch is right there too. When the case is rotated to a tower, the switch is on top.

Like one of these PSUs?
https://www.badcaps.net/forum/showpo...postcount=2986