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ATX Computer Power Supply Repair: I Learnt From My Mistake

By on July 24, 2014









atx power supply repair

I was given this Computer system because it was not powering up when they switch it on. When I powered it myself there was no any sign of life.

To open this Computer system I had to press a button and slide the side cover towards the front. Then I removed the power supply by moving it backward out of the clips. I unscrewed all the screws on the power supply in order to access the inside printed circuit board.


I started with visual inspection and there was not any sign of a damaged component. Then I tested the fuse by using my multimeter set on ohms range. I found out that it was open. I soldered the fuse out and tested again just to verify and it was indeed open. I recalled what I read from the SMPS E book by Mr. Jestine Yong that sometimes a fuse may blow either by itself due to life span or mild surge. Therefore, I just soldered my 100 watts bulb across the points where the fuse was.

I connected the power cable and inserted the plug to the power outlet. I switched on … what a spark!!! My God! As it sparked the bulb was giving out a very bright light. I immediately switched off. I checked what could be causing that terrible spark.

ATX Computer Power Supply Repairs

It was my silly mistake! The sharp edge of the cover of the power supply touched one of the EMI coils to the extent of removing the insulation and shorted it.

ATX Computer Power Supply Repairing

The spark burnt the coil and broke open its windings. The Printed Circuit Board was also painted black by the smoke produced from the spark.

atx power supply repairings

I believed the spark caused some damage to other components in the circuitry. Patiently, I started scrutinizing the pieces one by one with my meter. The capacitors and coil forming the EMI/RFI circuit, the Varistor, Bridge rectifier, the diodes on the secondary side of the switch mode transformer. In the circuit the Schottky diodes were showing low resistance. I removed them from the circuit and tested them separately. All were testing fine. I think it was the circuit network that was giving a low resistance. I had no means to test the IC.


Thank God nothing was victimized apart from the only two items; a fuse and a coil. I managed to get a fuse of the same rate (250 V 6.3A) from my old PCBs. I bought a new coil and fixed it. With the bulb connected I tested the power supply again and the bulb gave out light at once and then off. Yeah, positive sign.


I connected a jumper between the Green cable and the Neutral (PS – ON and Black) the bulb was giving out bright light ON ,OFF, ON, OFF …  During this time the fan was spinning with different speeds, fast, slow, fast, slow … as if it is trying to start and then stops. This is one of the possible outcomes when using a bulb trick on ATX power supply. Since I tested almost all components I expected that the power supply is trying to pick up but the bulb is reducing current necessary to power supply.

I removed the bulb and put a new fuse. Power up the power supply it was silent. I connected a jumper between Green cable and Neutral the fan rotated at a constant speed. I tested the voltage output with my meter set on DC Voltage range, all voltages were available. I assembled the PS and put it back to the CPU with all the connectors in their places. I switched ON the computer … Glory to God it is back to life.

atx power supply repairing

My mistake increased the job and made it more complicated. However, I have learnt from that experience to be always sure that there is no contact between the metallic covers and the PCB or the components of the equipments. I give my humble gratitudes to Mr. Jestine Yong for his informative, educative and down to earth E book on Switch Mode Power Supply Repair. The E – book was my companion during this repair and still will be in the other repairs to come.











Luciano Francisco Thomas Khware (Malawian) studied Electrical and Electronics at Comboni Technical College and at Polytechnic (University of Malawi). Currently, he is a student at Tangaza University in Nairobi Kenya.


Please give a support by clicking  on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments. By the way if you have any good repair article that you want me to publish in this blog please do contact me HERE.





  1. Robert

    July 24, 2014 at 9:23 pm

    Hi Luciano. Yes we have to be careful when powering up devices. I'm glad you got it fixed.

    • Luciano

      July 26, 2014 at 2:39 am

      year, Robert you are right! thanks for the comment

      • Richard DeKneef

        July 26, 2014 at 11:25 am

        Hi Luciano,

        A better thing to do when checking something that blows it's main fuse, is use a resettable fuse so when it blows you just press the button to reset it. You use one that is rated for the amps of unit under test and do not have to buy a lot of fuses. You have one set of resettable fuses that you use over and over again. Some manufactures have used a resettable fuse instead of a fixed fuse that you have to have extras on hand. I have seen this in some hi-power audio amps.

        If the resettable fuse pops right away, you have a problem and should start troubleshooting with no more power-ups. The power supply is always the first place to work since it is the "heart" of the device and then works the hardest. In audio amps, the output transistors are main culprits to short out and blow fuses quickly.

        And what a tech at a TV manufacture told me was to short out the fuse and then watch for smoke to find a problem. Not a good thing to do if you troubleshoot properly.

        Good job!

        • Luciano

          July 30, 2014 at 4:51 pm

          Richard DeKneef,
          I am really impressed with your comment, it is so informative. its my first time to hear about resettable fuses. I would like to have a link for further info.
          Thank you so much for your comment!

          • Richard DeKneef

            August 3, 2014 at 4:34 pm

            Sorry for late reply. I mentioned about a resettable fuse and I was wrong, it should be a circuit breaker which is the same thing somewhat.

            What you need is a circuit breaker that is rated 120v DC @ 60HZ or similar and at the amperage you need, 1 amp and up. This is something like you have in your home electric box for AC; if too much current, it pops the switch. You reset it and pops again, you have a problem. Sometimes a glitch will trip the switch and when you reset it, everything works fine.

            Low amperage circuit breakers will be small and various shapes. All you need is a circuit breaker of your choice and then solder a 4-inch wire to each connections on it. Then you have something that can be soldered in-place of the fuse in hardware being repaired with blowing fuse problems and not have to worry about buying a lot of fuses to have on hand in the process.

            Works great!

            Back later...

  2. john

    July 24, 2014 at 9:23 pm

    hi just read your article and found it informative I am repairing a cambridge azur 350c compact cd player and found the mains fuse blown when I used the bulb trick(first time) the psu was clicking on/off, I was of the opinion that the fault remained and was switching the relay on/off but having read your article will just try another fuse. I have done electronics for some years but its still possible to be fooled by the obvious regards john

    • Luciano

      July 26, 2014 at 2:53 am

      Hi John,
      the pulsating or flickering of the bulb is one of the outcome when you use a bulb in a power supply. flickering/ pulsating may mean that the power supply is trying to pick up but the bulbs wattage is not enough for the appliance. still you need to check if there is output voltage using your meter.

  3. Kevin

    July 24, 2014 at 9:25 pm

    Hi Luciano

    Good article as I think we have all done something like that in our lives, I know I have. The good part of the experience is that you did not get hurt and that you have learned something from it.


    Kevin G

    • Luciano

      July 26, 2014 at 2:57 am

      Hello Kelvin,
      Thanks! I was terribly scared! however the experience made me to carefully observe and assure that the equipment is safe before i power it up. its a lesson for life indeed.

  4. mosbad

    July 24, 2014 at 10:29 pm

    This repair job, the approach and the follow up technique is excellent, the mistake we talk about here is a common one that happens among we techs,sometimes we are carried off focusing on the next step and thereby overlooking minor precautions.
    Thanks for sharing this knowledge with us.
    God bless....


    • Luciano

      July 26, 2014 at 3:05 am

      Hi Mosbad,
      i thought it was just an easy fix,... an open fuse, and this made me to run into powering up without proper precautions. Never again!
      Thanks for your comment.

  5. Andre Gopee

    July 24, 2014 at 10:34 pm

    Thanks for sharing Luciano, Sometimes all of us at one time or another make mistake that cost us more in the long run... But the trick is to learn from them.

    • Luciano

      July 26, 2014 at 3:15 am

      Hi Andre,
      Its true, i learnt it a hard way. I took extra care during the second time i was testing!

  6. richard macphee

    July 24, 2014 at 11:13 pm

    You always have fantastic articals and great advice. Wish there were more guys like you out keep my ham radio stuff in good shape thank you

    • Luciano

      July 26, 2014 at 3:20 am

      Hi Richard,
      You are most welcome.

  7. Humberto

    July 24, 2014 at 11:19 pm

    Hi Luciano, good repair, keep up. One advise: when you test the SMPS, remember using loads, such as: HDD(s), Motherboard, etc. Have a good day.

    • Luciano

      July 26, 2014 at 3:23 am

      Hi, Humberto
      Thank you so much for the advise.

  8. Martin

    July 25, 2014 at 12:18 am

    The black wire isn't Neutral, its 0V. I think if you connected a link between the green wire and neutral (neutral being on the hot side of the power supply) then you may end up with a bigger fault than when you started.

    • Luciano

      July 26, 2014 at 3:40 am

      Hi Martin,
      Thanks so much for the observation! you are right. i think it was not on the hot side, but the safe side because the power supply did not explode again.

  9. yogesh panchal

    July 25, 2014 at 12:45 am

    good work keep it up and thanks for sharing the article.

    • Luciano

      July 26, 2014 at 3:41 am

      Hi Yogesh,
      You are most welcome!

  10. Merlin Marquardt

    July 25, 2014 at 12:46 am

    Interesting and instructive. Still don't understand the light bulb "trick". Thanks.

    • Luciano

      July 26, 2014 at 3:55 am

      Hi Merlin,
      You are most welcome! for the light bulb trick i advise you to purchase the E - book Troubleshooting and repairing SMPS by Mr.Jestine Yong (chapter 13, pp 154 - 160) you will surely get it!

  11. Dwight Baker

    July 25, 2014 at 1:40 am

    There are very inexpensive power supply testers available here in the US and I am sure worldwide via ebay for about $10 that allows you to verify the PS without plugging it into a motherboard. I have blown a motherboard testing power supplies so the $10 or less is a good investment. I see this one which is very similar to mine for only $4.88 with free shipping to US from US.

    • Doug Jones

      July 25, 2014 at 2:28 pm

      Thanks for the suggestion, just ordered mine.

    • Luciano

      July 26, 2014 at 4:03 am

      Hi, Dwight Baker
      I appreciate your comment and all the information therein. thanks for the link as well. does the shipping includes countries in Africa, like Kenya? i would like to have one.
      thanks once again!

  12. Mervin

    July 25, 2014 at 1:57 am

    well done finally

    • Luciano

      July 26, 2014 at 4:11 am

      You are welcome.

  13. Abdul

    July 25, 2014 at 9:38 am

    Thank you Luciano for your article.
    Hope to hear more from you.

    • Luciano

      July 26, 2014 at 4:15 am

      Hi Abdul,
      you are most welcome, i learnt a lot from peoples experience and sharing, i am ready to share both my success and failures as well.

  14. Mark

    July 25, 2014 at 10:04 am

    Thanks for your honesty Luciano. We have all made mistakes like that at one time or another.
    It is something you will never forget and never you won't do again.
    Thanks for sharing.

    • Luciano

      July 26, 2014 at 4:33 am

      Hi Mark,
      I can assure you that I will not wish it to happen to me or anyone again. Its better to practice patience making sure that there is proper insulation and the power supply is safe before powering it up!
      Thanks for your recommendation

  15. Wilson

    July 25, 2014 at 11:32 am

    Thanks guys your articles and comments have helped me learn and understand many concepts and skills in repairing devices.

    • Luciano

      July 26, 2014 at 4:40 am

      You are right Wilson, Sharing of Knowledge and experience helps a lot.
      I also get insight from this blog

  16. Derek Mervyn

    July 25, 2014 at 3:33 pm

    Excellent article----My experience is that whenever PCBs are to be tested one must make double sure that nothing is touching any ground points and first time power up should be done with a lamp in series.Thanks.

    • Luciano

      July 26, 2014 at 4:44 am

      Hi Derek,
      Year I fully agree with you and thats exactly the lessons i learnt this time.

  17. marwan

    July 25, 2014 at 3:56 pm

    green cable and black .short power start

    • Luciano

      July 26, 2014 at 4:57 am

      Hi Marwan,
      Shorting PS - ON and Green switches the Power Supply ON isnt it? i think its what i meant.

  18. hongkongpom

    July 25, 2014 at 11:20 pm

    Thank you for being humble and admitting your error. It is something that we all go through sooner or later!

  19. Joshua oloo

    July 25, 2014 at 11:37 pm

    Hi Luciano,Am really impressed with your Article.Can one use 10 Ohms 10 W resistor as a load to test the volt. on the 20 pin Atx connector?otherwise its been great learning from you.God bless you

  20. Luciano

    July 28, 2014 at 2:46 pm

    Hi Mr Joshua,
    I would say yes its right to connect a load when testing ATX power supplies because some of such power supplies require a load to be connected in order for them to work.
    Thanks so much!

  21. michael

    July 29, 2014 at 7:01 am

    thank you for being so honest to admitting your error, it could happen to the greatest of technicians,i an glad you fix it.God bless you brother

    • Luciano

      July 30, 2014 at 4:53 pm

      You are most welcome! Thank you so much for the Blessings! May you be blessed too.

  22. Luciano

    July 29, 2014 at 2:30 pm

    Hi Mr.Joshua,
    There are some ATX power supplies that do not switch on unless you connect a load. Therefore,in such cases, when testing to connect a proper load to the Power supply would be the better idea than testing on no load.

  23. beh

    July 30, 2014 at 7:55 pm

    LUCIANO: yes .this is the way of progress do not afraid of mistakes and try to improve knowledge and experience to solve the problems
    keep it up and thank you

  24. Anthony

    August 10, 2014 at 7:02 am

    Have you ever try to replace an open pico fuse from a big xformer before?I never forget how I found an open pico fuse on a big pwr supply with a big xformer that was used on a special medical equipment as a backup pwr in case the pwr go out at the hospital.Would you like to know how I found that open fuse? A special meter called the,"LOW OHM METER.Addio! Which also mean ,"good-bye" in Italian.

  25. fayaz

    August 13, 2014 at 7:33 pm

    I love ur every post
    How can I buy your books I belongs to a poor faimly I can. T effort your books sorry

  26. Raymundo Saura

    August 27, 2014 at 3:56 pm

    thanks sir


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