Electronics Wizards. Power Supply Repair Question.

[jaydee]

Alright I had 2 PC power supplies I brought to work today to see if I could fix them. One had a blown Cap which was pretty simple. Just replaced it with the same cap and it works.

But the next one has me baffled a bit. When you trip the power on it will power up for a few seconds then power down and stop. I thought it might be the two big Caps, but I replaced those and still the same problem, but then again the replacement caps are used so they may not work. But before I get new Caps does this sound like a logical solution or do you think something else maybe wrong. It powers up for maybe 2 second and then dies. With the Volt meter on it goes right up to where it should be on the 12V and 5V rail but then just dies all together after the few seconds. It is a nice power supply and hate to scrap it.

Any ideas?

[bigben2k]

Are these ATX supplies?

What should be happening, is that the PSU is detecting a false overload condition.

The motherboard connector might have some pins with two wires connected to them: the thinner wire is a voltage regulating line. The +12 and +5 lines at least, should have them. You can try cutting those, but I don't think it's going to be any help.

You're trying to force them on with some kind of load, right?

[jaydee]

Originally posted by bigben2k
Are these ATX supplies?

What should be happening, is that the PSU is detecting a false overload condition.

The motherboard connector might have some pins with two wires connected to them: the thinner wire is a voltage regulating line. The +12 and +5 lines at least, should have them. You can try cutting those, but I don't think it's going to be any help.

You're trying to force them on with some kind of load, right?

Umm all you have to do is jump the power on wire (green in one supply and grey in the other) with the ground.

Fires them right up. The one I replaced the blown cap stays on just fine, it is the other one that turn off. It was doing this while attached to the computer aswell, thats how I found out it was messed up and ended up killing a perfectly good Epox 8K7A thinking it was the board becuase the supply would fire up and then stop. The fans and the lights on the comp would go on then stop. Same thing hppens to the power supply fan when I jump the power on with the ground, fires up then slowly stops. Maybe this supplu has advanced overload protection as opposed to the other? Still wouldn't explain why it wouldn't work with the Epox board though.

[bigben2k]

I'm aware of how to jump a PSU :P The issue is that some of them don't take well to being jumped without a load.

So it might be an overload condition: try loading it with a tester resistor, or a few fans. You should put a load on both the +5 and +12.

Maybe the board was dead, and is causing the PSU to overload

[jaydee]

Originally posted by bigben2k


Maybe the board was dead, and is causing the PSU to overload

I tried it on my ECS K7S5A which is happily working as we speak (different supply of course), thats how I discovered it was the supply and not the board. Unfortuantly I killed the Epox before trying a different supply by replacing the bios with another off an older board. Well I can't get it to work anymore... My own dumbass fault. But anyway I will hook it up to the ECS again when I get home and see if it works or not. I never had a ATX supply not fire up by jumping it though. Usually the power supply 80mm fan will spin happily untill you unjump it. Even workes on my Antec 300watter. Not the case with this one. Will double check and post back later tonight.

[jaydee]

You the man Ben! Plugged it into a mobo and it works! Woot!

[bigben2k]

So maybe you accidentally flash fried the BIOS on that Epox?

[jaydee]

Originally posted by bigben2k
So maybe you accidentally flash fried the BIOS on that Epox?

Possibly. Wouldn't explain the PS not working on the ECS board aswell though, unless some other fluke happened on it and shorted the supply out. The two big caps were starting to bulge pretty good on the tops. I figured it was them. Might resolder in the originals and see if it still works. Might have all just been a bad set of coincidences.

Well off to do some milling..... I will mess with the Epox again sometime this weekend to see if I can bring it back to life. I already fired up my old Abit KT7A. Hard drive controllers are still dead but I got a PCI hard drive controller somewhere around here I am going to drop in to see if I can get it to work. Need more Distributed Folding crunchers.