Repair ATX power supply

These power supplies are replaced, and not repaired. The time and cost is not worth it.

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JANA _____

I was wondering does anyone here have a good guide for how to go about repairing an ATX computer power supply ?

I've never done anything like this before, so any help is appreciated..

Chris

If you have a way to operate the supply without it connected, and you can have the schematics, and necessary test gear, go ahead and start troubleshooting. It can be as little as a simple component, to an array of parts!

Take care when working on these switching supplies. The drive voltage and drive current can be lethal!!!

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JANA _____

I have replaced the power supply, and now I want to repair the old one.. I shouldn't have to throw out a $50 peice of equipment because a 25c part is broken.. (spending a day or two finding the problem doesn't worry me)

The problem is that it still supplies +5V standby, but refuses to turn on (I have a load attached and I do have the correct wires for PS_ON and ground).

No fuses are blown, and nothing appears or smells obviously burnt.. I was told to check for open/high resistors near the large filter caps on the high side, so I did and they both read the correct ~220Kohms.. there's two diodes on the high side and both those are ok also.. what else should I test ?

Chris

Could be.

Throw it away. At this point, not only will it cost more to replace all the bad parts than buying a new spare supply, you're likely to never repair it as many other things can blow, and if you fail to find even a single one and replace it, they may all blow again instantly.

--- sam | Sci.Electronics.Repair FAQ:

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Maybe.

Graham

Not to be mean but if you you don't know something basic like what these reading mean it's not likely you're going to repair this device by yourself.

On Sun, 25 Nov 2007 07:07:47 -0500, "Skeleton Man" put finger to keyboard and composed:

I find it strange that your chopper (?) transistors/MOSFETs are shorted C-to-E or D-to-S, yet the fuses are intact. Maybe you have an open NTC resistor ???

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

It's more an exercise in troubleshooting and repair than anything.. If I wanted a spare I would buy one..

Also, if I can repair a $30 power supply, the same basic skills should apply to a $200 power supply.. you wouldn't just throw it away and buy a new one then.. (doing component level repairs is an an extra skill I'd like to teach myself)

Chris

Yes, you can buy replacements, what are the numbers on them? Make sure you check all the other semiconductors, this sort of repair is challenging, if another defective part remains, everything you replaced can blow again before you know what happened.

He said the fuse blew.

Doesn't work like that in real life.

The parts alone will cost more than the replacement of the power supply. Likely even for the $200 power supply.

And whether or not you like it, your time IS worth something, and it's usually a LOT more than a measly $200 for a power supply.

There may be some conditions that control this, such as this may be a special-purpose supply that can't be replaced, or off-the-shelf replacements are not available for some time, and you can fix it faster than the time the replacement comes in.

And, from what you've described, it doesn't appear you're up to the task anyway, and 'fixing by correspondence' doesn't work in this case. Much like trying to get your mother to completely dismantle your car engine, repair and reassemble going off instruction on usenet.

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Linux Registered User # 302622

Huh? I've repaired a lot of power supplies over the years, and never encountered one where anywhere near $200 in parts was required.

The value of the power supply is nothing compared to the value of the education it could provide. When I started repairing things, I learned by working on equipment that was mostly pretty worthless, some of it I fixed, some of it I broke worse, the odds steadily improved with practice. You've gotta start somewhere.

Sorry, but SMPS's are A REAL BASTARD to diagnose and repair... that's why so many very competent professionals who repair electronic gear for a living have suggested that you throw it away. It's like saying "I'd like to learn math, and I'm going to start with this advanced calculus text." If you want to learn to fix something, choose a) something fixable and b) something worth fixing. The way in which switch-mode power supplies operate makes them by nature dangerous to work on as well, which is less than ideal for a novice as you really can hurt yourself.

Good luck.

Dave S.

Another thing to consider is: Would you trust that repaired power supply to be a spare for your new turbo-charged PC if its power supply dies, given that you may have barely understood what you did to get it working?

--- sam | Sci.Electronics.Repair FAQ:

Repair | Main Table of Contents:

+Lasers | Sam's Laser FAQ: | Mirror Sites:

Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

Yes. You can probably replace them with about any high voltage transistors from another PC PSU, even an old AT one, provided they're they same type (NPN) and are rated for at last as much voltage, current, and power. But if the new ones come in different packaging you may have to add electrical insulation, such as a silicone rubber transistor insulator sheet between the transistor and heatsink or a flanged nylon washer for the mounting screw, emphasis on "flanged". Be absolutely certain that the transistors are insulated from the heatsink or they'll instantly blow out when the power is turned on. BTW the heatsink for those transistors is often connected directly to about 350V DC, so don't plug in the power unless the PSU cover is installed and screwed on.

A spec sheet for the 2SC2625 can be seen here:

www.ortodoxism.ro/datasheets/mospec/2SC2625.pdf

This website:

has information about computer PSUs, including schematics for a couple of them.

I think that your PSU has three transformers: main, standby, and one to drive the high voltage transistors. The fourth thing that looks like a transformer (in the lower right of your picture) is actually an AC line filter (OK, it works as a transformer).

That is EXACTLY what I am talking about ! (just written better lol)

Chris

so

want

I'm a novice but not a newbie.. I have studied basic electronics dealing with how various components work, etc.. I taught a bit about building stuff, just nothing about repairing it..

"Gee.. what's this big round thing ? I might stick my finger on it.. ZAP!" - Not quite that novice..

Chris