Faulty PSU Revival

Thread Starter

b_gravedigger

Joined May 12, 2009
6
Hello everybody,

A faulty PSU recently came to my possesion and i need some advice on how to revive it, if possible.

It was part of a desktop whose motherboard, vga and hard disk were rendered useless, possibly due to a spike in the supply voltage.

To the point:

When i connect the power supply to a working motherboard and try to turn it on, it seems completely dead. Same thing happens when i connect it to the xilence power supply tester.

Upon opening the case i noticed 2 burnt resistors, 2 damaged ones and 1 burnt transistor (that one actualy fell off it's place when i touched it).
Here, you can see the clearest photos i could take.

The first step of the revival process would be to replace the faulty components (or at least the ones that seem to be faulty). But is there a safe way to replace a resistor, whose value i don't know (for the ones that are completely burnt)?
Also, the code K619 C945 P is written on the transistor, but i can't find it's datasheet, so i can't find a suitable replacement for it.

If there is another way of dealing with this piece of equipment, i would be happy to know.

Thanks!
 

Georacer

Joined Nov 25, 2009
5,182
Do me a favor lads and solve this guy's issue. If we come up with empty hands I 'll hear no end of it about how I run my home forum, as opposed to his "awesome" moderating back here in Greece.
 
Last edited:

paulktreg

Joined Jun 2, 2008
784
If you are repairing this power supply because you really need it or just for the experience then fair enough but god it's old!

I can see a white wire there that's -5V that was made obsolete ages ago and it obviously hasn't got any power factor correction. Unless you're still running the older ISA cards you could probably pick up a replacement of equal (low) quality for about £10~£15! ;)
 

Thread Starter

b_gravedigger

Joined May 12, 2009
6
If you are repairing this power supply because you really need it or just for the experience then fair enough but god it's old!

I can see a white wire there that's -5V that was made obsolete ages ago and it obviously hasn't got any power factor correction. Unless you're still running the older ISA cards you could probably pick up a replacement of equal (low) quality for about £10~£15! ;)
Oh yes, it's old :)



I do need it, as i have an old 478 socket mobo with a pentium 4 waiting to become my new old-desktop, but i also cannot live with the idea that all those goodies attached on the pcb are useless because of a couple of burnt resistors.
 

paulktreg

Joined Jun 2, 2008
784
If you are dead set on fixing it (I think you'll struggle to get the value of those resistors though) then I'd also replace all the electrolytic capacitors.

Do yourself a favour and spend a couple of quid on a new one! :D
 

jaygatsby

Joined Nov 23, 2011
182
Good exercise but consider this: if you are going to use the supply with a decent, high speed computer, forget it and get a really nice $100 supply from newegg. Good, fast computers can have issues with crappy supplies.
 

SgtWookie

Joined Jul 17, 2007
22,210
If you're dead set on fixing the supply, the first thing you'll need to do is to get all of the crud off of it. Start with compressed air (or canned air if you don't have an air compressor). Then start getting the rest of it off, using isopropyl alcohol (90% or better) and a small coarse-bristled brush.
 

spinnaker

Joined Oct 29, 2009
7,835
Oh yes, it's old :)



I do need it, as i have an old 478 socket mobo with a pentium 4 waiting to become my new old-desktop, but i also cannot live with the idea that all those goodies attached on the pcb are useless because of a couple of burnt resistors.

Old??? Unless it has tubes in it, it is no were near "old". :)
 

Georacer

Joined Nov 25, 2009
5,182
And then, what will the next step be? Will there be possible to find any schematics for it, or using some range of standard resistors?

Tracing the board will be unproductive, won't it?
 
It was part of a desktop whose motherboard, vga and hard disk were rendered useless, possibly due to a spike in the supply voltage.


Upon opening the case i noticed 2 burnt resistors, 2 damaged ones and 1 burnt transistor (that one actualy fell off it's place when i touched it).
And those are only the things you can see. ;)
I've circled what appears to be a bad cap.

I agree with the other posters in that it would be easier (and, in the long run, cheaper) to just get a new one.

But, that's just my humble opinion.
 

Attachments

SgtWookie

Joined Jul 17, 2007
22,210
Here is a link to a slew of computer power supply schematics:
http://danyk.wz.cz/s_atx_en.html

After you get the supply pretty well cleaned up, find the regulator IC. It'll most likely have somewhere between 8 and 18 pins. Get the part number from the IC, and see if it is close to any of those listed on the above page.

You may have one or two TL431's or equivalent used as voltage references; the regulator IC will be close by. You will also find an optocoupler/optoisolator or two; these are used to send feedback from the secondary side back to the controller on the primary side.

Establishing what the controller is, and what relationship the fried components have to the controller, will help a great deal in establishing a reasonable range for the components.
 

Thread Starter

b_gravedigger

Joined May 12, 2009
6
Here is a link to a slew of computer power supply schematics:
http://danyk.wz.cz/s_atx_en.html

After you get the supply pretty well cleaned up, find the regulator IC. It'll most likely have somewhere between 8 and 18 pins. Get the part number from the IC, and see if it is close to any of those listed on the above page.

You may have one or two TL431's or equivalent used as voltage references; the regulator IC will be close by. You will also find an optocoupler/optoisolator or two; these are used to send feedback from the secondary side back to the controller on the primary side.

Establishing what the controller is, and what relationship the fried components have to the controller, will help a great deal in establishing a reasonable range for the components.
Now there's some usefull advice. I will look into it and keep you updated.

Thanks a lot everyone.
 

tom66

Joined May 9, 2009
2,595
It looks a bit like Bestec. These power supplies have been known to cause the 5VSB to hit 17V due to a bad capacitor, and kill motherboards. They usually kill their controller chip eventually as well.
 
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