ATX Power Supply REPAIR

Hi, everyone!

My computer ATX power supply, have been burned caused by a peak of current, I've opened it, and I saw the fuse, it was blown, I have replaced it, but.. when I turned on the power supply, the fuse did not blew, but I've heard a sound like a speaker with some noise. I don't know where that soound is coming, but I watched that the big capacitors, the only two real big, seemed that they have been eaten too much... Because they're a little fat in the top, actually one of them has a thing like paper "leaking" int the top.

My question is does it worth to substitute the capacitors, or even if I substitute the capacitors, may I have to continue substituting components, over and over .... ?

Thanks 4 any help.

Regards, Helder Silva

hi HelderS
i have had this fault in my power supply before and changed the two mains filter caps and it worked fine .. may all u need to do is to substitute those two caps only and it'll work fine . this is due to power surge
yes u can substitute any thing but not necessary to do that , just change the two caps and see .. it's easy to repair it but may be didn't worth if u have more components to replace , go for new one better.
i mean just change the two capacitors and see if it worked fine it's ok , otherwise go for new one as it's cost is less than replacement parts with time spent in repair.
one more thing .. if it didn't work after changing the caps go to see open resistors on the primary side of the power supply it costs nothing but if u have to chang switching transistors and the othe stand by transistor and so on .. go for a new power .
regards

Use an Ω meter to measure resistancies of all components around the switching transistor, including all diodes, rectifying bridge, resistors, etc. If you find any suspicious measurement (close to 0Ω) check this component, and if necessary replace it ..

Hi, again, and thanks...

I would like to know how can I test the Power Supply, without connecting it to the Motherboard.

Thanks a lot

Regards, Helder Silva

Because it is smps you will need some load.
If you have a 12V/50W car bulb at hand you can connect it to 5V/12V pins; it should provide +/- sufficient load to operate under this condition ..
A wire/wound 5/10W resiswtor of 10Ω or smaller on the 5V rail would do the job ..

Once you flipped the power switch on the ATX power supply to on (some ATX power supplies do not even have such a switch), the ATX power supply sends a 5V (min 1A) current to the motherboard through pin 9 (5VSB) (violet color wire) on the power connector.
You should be able to measure this voltage with a voltmeter.
If everything it's OK you can now identify pin 14 (PS-ON) (green color wire), which is power-on pin, you can using a piece of wire short the pin 14 and 15 (black). If you power supply has power connected to it and power switch on the power supply is on, you will see the fan is turnning by now.
Pin 8 (grey color wire) it's PWR_OK. It's an ordinary TTL output that should be asserted high by the power supply to indicate that +12VDC, +5VDC and +3VDC outputs are above the undervoltage rated tresholds and that sufficient mains energy is stored by the converter to guarantee continuos power operation within specification.
If none of this happens then you should not plug into your motherboard.

Hi, again!!!

I would like to share something with you, in the circuit of the ATX PS, the caps seem to be good, but a thermistor near the fuse is missing a piece of it. Although, it presents a normal value. Now, I don't know much more I can do, I'm going to try the posters advices, and then, I think I'll buy a new one.


REgards, Helder Silva

I am also having problem in smps my problem is that +5v in pin 9 works, but i could not switch on the smps what should be the problem and also this is caused by fluctuation in current.

Hello,
If yours power supply it burns the fuse the causes can be two. Transitor of power é in short circuit or the primary of the transformer é in short circuit. I you council to replace the power supply because if it had to go in short circuit the primary with the secondary one you would burn your PC.

Added after 1 minutes:

Hi,
If yours power supply it burns the fuse the causes can be two. Transitor of power é in short circuit or the primary of the transformer é in short circuit. I you council to replace the power supply because if it had to go in short circuit the primary with the secondary one you would burn your PC.

how can i measure resistancies with meter that its ok or not ok .