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400 Watt PC Power Supply Repaired

By on November 9, 2015
400 watt pc power supply repair









About a week ago my E3400 dual core pc suddenly stopped working. And I didn’t knew what happened because it happened while I was busy with backing up important data about electronics. It was if had a Power Loss at home. The Fan of my pc Power Supply stopped turning and with a unexpected silence my pc was dead.

I first checked if anything else at home still worked and everything did, except of course my pc. So because it was no power loss, I opened up my pc and first checked the Power Supply. There was nothing burned or anything visible that could explain the reason why it had stopped.

But since I had no equal 400 Watt supply and I needed my pc badly to finish my work, I decided to use an older 300 Watt ATX supply instead. And later on when I had more time I would check if I could repair the now defect 400 W ATX Supply.

And today the 26 of October I was finally ready to check the inside of this Switching Power Supply. Next photo gives the specs of this model ATX-400W / LP-6100. My first thoughts were that probably another electrolyte capacitor had given up. I used my MESR-100 ESR meter to check for bad ESR values. And I checked all of them but they all were fine! (Also I could have used my Blue ESR/Low Ohms meter from Anatek Corp. for this). I also checked all Capacitor values with the M6013 meter. And all measured within their given value as written on the caps.

400w atx repair

Next photo shows the AC Power Input side.

power supply fan

So because the Capacitors all checked fine, I had to look further for the reason why my ATX Power supply gave up on me after about 4 fantastic working years. But according to the sticker on the outside it was manufactured somewhere in 2005. I bought it second hand so the ATX supply already had worked much longer before I had it.

Next I checked on the bigger resistors with often low values. They all checked fine too.

It was obviously no short circuit either, because the supply just had stopped in the middle of my work. And I had to look further so next I removed the secondary semiconductors from the pcb. Not by using a vacuum desolder pump. But just by desoldering the Aluminium cooler plate and all the attached semiconductors together by using enough solder and my solder station (My 25 year old trusted Ersa MS6000 !) at the right temperature. And when you do this carefully one side at the time, back and forth, over and over again until all components are nicely removed, parts and pcb won’t be damaged afterwards. This is the best desolder solution in these special cases when the desolder Pump just doesn’t work because the holes are too small to free the component pins. And after you removed all components with cooler and all, you are much better equipped to open up the now empty holes with that same desolder vacuum handpump. Doing it differently will damage your pcb or break component pins and you won’t be able to remove the semiconductors at all!

There were 3 components on the secondary cooler. All were dual diodes, and one was very big for obvious larger currents. They all checked okay too. And after this cooler was removed I could better view all other parts including the primary cooler. Next photo gives an idea how the supply looks on the inside.

400 watt atx circuit board

Previous photo shows the inside of the ATX power supply with the secondary cooler plate removed. With on it the 3 dual diode semiconductors. In the back of the previous photo the primary cooler plate is visible.

Next photo shows the secondary cooler with the checked okay components.

atx power supply repair

As you can see no parts were harmed while taking previous photo (LOL). And I checked this secondary cooler plate first because I was thinking that the big semiconductor maybe was a defect switching Mosfet or Transistor. But it checked out it was only a very big Dual Schottky Diodes.

I checked all parts with my digital semiconductor testers. I have 3 different testers. I had built my first one from a project in Elektor called the SC2005 tester that got a firmware upgrade a few years ago from the author of this tester. But as it turned out to my surprise it gave wrong values while testing one of the semiconductors on the primary cooler plate.

But first next photos show you what the solder side of this board looks like with the secondary plate removed. The open holes show you exactly were the plate with the 3 dual diodes was soldered.

And the 2 photos after that show you the controller IC (a PWM controller 494 probably Texas Instruments) and a LM339 (a quad voltage comparator). Both are placed right next to the secondary Cooler plate.

atx circuit board repair

repair 400w pc power supply

Finally I found the cause of this suddenly bad ATX supply on the primary cooler plate.

Next photo shows the primary cooler plate before removing from the board.

atx repairing

My Semiconductor tester 2005 (Elektor 2005 + FW update, new IC) on previous photo sees the MJE13007 as a PNP transistor which it clearly is not! But the SC2005 tester checks correctly that the Bad MJE13007 is shorted internally. A Bad MJE13007 which is cause of this failing Power Supply.

china transistor tester

My China tester (2014-07 by FISH8840) correctly gives a NPN type. But it looks like the symbol of the transistor has a wrong PNP arrow direction. Because the Emitter arrow direction in a NPN Bipolar transistor normally goes out of the transistor. (And it here clearly goes into the Emitter)

transistor tester

Also there probably is no internal diode going internally from point 3 to point 2. At least the datasheet of the MJE13007 doesn’t show any diode either!

From the two MJE13007 transistors was the middle one short circuited on the primary cooler plate. After replacing it by a new MJE13007 the 400 Watt ATX power supply works like new again!!

These Bipolar transistors continuously can switch 8A at max 400 Volt DC. And are specially intended for Power supplies and capable to withstand reverse high voltages up to 700 V! And a power max of 80 Watt.

And before you all react in saying that the price of a new Power Supply is just about 35 Euros/Dollars or whatever. Let me remind you that the cost of a single MJE13007 is close to nothing!! And that was all that took to repair this fine 400 Watt Power Supply for the next years of continues operation.

Following the datasheet of the MJE13007 Bipolar switching transistor.

mje13007 datasheet

mje13007 transistor datasheet

mje13007 npn transistor

On above datasheet you can clearly see the right symbol for the MJE13007.

Last but not least 2 photos that unmistakenly show that the Power supply repair was a great success !

atx power supply tester pg

The FAN is also turning. And the Power supply tester proofs that all voltages are fine! Another Switching Power Supply repair successfully completed.

Thank you for reading, until another repair!



Albert van Bemmelen, Weert, The Netherlands.

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P.P.S- Note: You can also read his previous repair article below:

P.P.P.S- If you wish to learn how to repair switch mode power supplies like a Professional, please click HERE.




  1. Francis Fernandes, Mumbai, India

    November 9, 2015 at 1:32 pm

    I am interested in receiving the circuit of your testers including Blue ESR meter.
    Thanks very much

    • Albert van Bemmelen

      November 9, 2015 at 9:37 pm

      Hi Francis, most testers I bought are commercially sold and do have protected
      Firmware burned in microcontrollers. The Blue Ring and Blue ESR testers for
      instance are sold in the USA by Anatek Corp. You probably are able to buy
      them a bit cheaper as complete DIY KIT. And the Blue ESR meter was originally
      designed by Bob Parker. The Elektor Semiconductor tester is published in 2005
      and you maybe are able to find the Firmware on the internet and the Elektor
      magazine in which it was published (Dutch Elektor April 2005,
      pcb projectnumber 030451-1). The update firmware flashed PIC controller for
      this SC2005 (also called PRO DETERMINATOR - French?) can however only be
      bought from MWinstruments. Recently I bought a dirt cheap tester that you
      most likely will appreciate more that also is able to test semiconductors
      plus LCR components AND also ESR of capacitors amongst other things.
      See this link:
      -Tester-Kit-LCR-ESR-PWM-p-986954.html . Hope this answers your question.

  2. Pepper

    November 9, 2015 at 10:51 pm

    Excellent example of persistence Mr.van Bemmelen!
    Good job!!! Also the adage, "a `guilder' saved is a guilder earned" comes to mind... (-;

    • Albert van Bemmelen

      November 10, 2015 at 1:30 am

      Thank you Pepper, many other sayings come to mind that could convince a
      person to be carefull with spending his money. Just like they say:
      Money doesn't grow on trees, Money is a good servant, but a bad master,
      A fool and his money are soon parted etc. And while repairing electronics
      it always how not to spent it. The English word for the Dutch Gulden
      (used to be a value of about 0.45 Euro) is Guilder (that originally was a Golden coin).
      Of course this has little to do with electronics although we can make as you
      probably know a point-contact diode with a needle placed on a metal coin.
      In a way that is how the old germanium diode works. By placing it in the
      right spot it can be used to recieve and detect AM radiostations.

  3. Merlin Marquardt

    November 10, 2015 at 1:29 am

    Very nice. Very detailed.

  4. Albert Hoekman, Holland

    November 10, 2015 at 3:26 am

    Hi Albert, nice and well explained article.
    Also the man on the avatar looks good. LOL.
    I like to know where you buy the parts you need, like the MJE13007.

    • Albert van Bemmelen

      November 10, 2015 at 9:44 am

      Hi Mr.Hoekman, to keep me from using my own name (Haha). As you probably
      know I seldom buy parts in my (and also your) country.
      Mostly I wait in patience on parts ordered from China through Ebay.
      Because many components are here often hard to get and at prices that
      could pay you a retourticket to China. Sadly the MJE13007 recently was
      more costly on Ebay than it was about 8 months ago. You see,
      I had ordered a couple of them before but for that price you now only
      get 1 or 2 of them. So it happens that components are less available too!
      I guess that with the avatar you mean the photo that always keeps popping
      up under any of my later articles? Normally I never take any photos.
      That is of myself I mean, but this one was made after succesfully fixing
      the Tektronic 500 MS/s 2440 Memory Oscilloscope for my friend
      and old colleague Frans.

  5. Gary Gemmell

    November 10, 2015 at 6:08 am

    Love it Albert its great to see another environmentally conscious person like myself
    - I never throw anything out i always repair even the smallest item.

    You are correct since i bought one of these chinese testers it has made
    life very easy and quicker to fix problems.
    I think they are known as Mega328 testers.

    Cheeaper and easier to buy one already constructed.

    • Albert van Bemmelen

      November 10, 2015 at 10:00 am

      Hi Gary, indeed the Mega 328 tester is well known. And probably a
      new version from the original Avr transistor tester. There are
      about 20 different versions on Ebay sold from China.
      See this link that includes schematics and links to the
      firmwareversions too:
      or this link: or here:
      or the projects here:

  6. Chris

    November 10, 2015 at 8:45 am

    Thank's for sharing, I love this repair guide! its so clean
    and easy to follow the instruction with all the datasheet.
    Just perfect.

    • Albert van Bemmelen

      November 10, 2015 at 3:54 pm

      Hi Chris, it was afterwards an easy repair but both my used
      Transistor/Semiconductor testers went wrong in giving the
      correct information.And I think it was, as you can see in the
      MJE13007 datasheet, because of the very different and high
      currents in Base opposite Collector/Emitter. Compared to more
      normal triodes the Base here also is able to conduct very
      high currents! The MJE13007 Base current can be as high
      as 4A and that is also why the Emitter conducts here a max
      of 4 + 8 is 12 Ampères! Which is also much higher than
      the Collector current that normal is about equal to Emitter current.

  7. Suranga Electronics

    November 10, 2015 at 1:29 pm

    hi. Mr, super one Repair. thanks for the Article

    • Albert van Bemmelen

      November 10, 2015 at 4:07 pm

      Thank you Mr.Suranga. While repairing again another ATX Power Supply
      I found out that the fixable supplies mostly are the ones with
      a single bad Electrolite Capacitor (mostly small ones like 4.7uF 25V).
      Or the ones that do not use too many different ICs or controllers
      at the primary side! Because the more unrepairable supplies mostly
      do contain parts that are likely the heart of the not working
      SMPS supply. And most likely contain a bad switching mosfet
      in their controller circuit.

  8. Yogesh Panchal

    November 10, 2015 at 4:08 pm

    Good Job!
    Thanks for sharing.

    • Albert van Bemmelen

      November 10, 2015 at 7:33 pm

      Thank you Mr. Yogesh. It was my pleasure sharing it !

  9. Parasuraman S

    November 11, 2015 at 12:50 am

    Great Job! The way you have hunted for the defective component,
    reminds me of a lion or tiger hunting for its food!
    Shows the grit and grin! All the best!

    • Albert van Bemmelen

      November 11, 2015 at 11:15 pm

      Thank you for your very kind words Mr.Parasuraman. But I guess
      I am a very lousy Hunter. And all the better for the already
      poor population of Tigers or the in the wild living Lions.
      Or for that matter how the Orang-utan in Indonesia is in trouble
      because of the burning Forest. I only saved another single
      ATX power supply, but maybe by showing how I did it, with me
      now hundred of others to save a piece of the environment.

  10. Robert Calk

    November 11, 2015 at 1:39 am

    Good job, Albert. My Hakko 808 has different sized
    nozzle tips. It really is the best money I have ever spent.

    • Albert van Bemmelen

      November 11, 2015 at 11:27 pm

      Hi Robert, I know and I also would be very interested in a Hakko.
      But living in Europe makes buying a Hakko because of the Import
      costs much more expensive. I guess living in the USA is better
      if you can buy it in your own country. Like for instance the
      problems we in Europe have while just bying a single little
      battery for the Tektronix Oscilloscope. But Ebay doesn't sell
      the 808 anymore. Now it is the replacement Hakko FR300-05/P
      costing $265 US dollar + $52.90 Shipping (import EU from the US).
      Is way over my buying price !! See:

    • Albert van Bemmelen

      November 12, 2015 at 6:06 am

      I know Robert but spending $265 plus almost $52.90 dollar
      Shipping and Import is a bit too much for my taste.
      Plus there are no extra nozzles in the Hakko FR300 05 P
      standard replacement for the old Hakko 808.

      • Robert Calk

        November 12, 2015 at 12:22 pm

        There are companies in Europe where you can buy one.
        The European model is Hakko 888.

        • Albert van Bemmelen

          November 12, 2015 at 3:08 pm

          Thanks Robert. I have taken a look on that Hakko model
          you mentioned on Ebay. It is only for soldering.
          And it is not a desoldering Pistol either!
          About $100 dollar would make the price okay
          but I already own a perfect Ersa MS6000
          solderstation and 2 hot air units for soldering.

          • Robert Calk

            November 13, 2015 at 5:03 am

            I apologize Albert, I guess they changed the number.
            Last year when I read about it, they said the European
            model like the US model 808 was going to be the 888.
            I guess they changed their mind for some reason.
            Anyway, here is their site with some de-soldering guns:

            • Jestine Yong

              November 14, 2015 at 10:04 pm

              Hi Robert,

              This post Reply button seems to have problem and Albert
              have asked me to post this:

              And that the Aoyue Desolderstations are at least 33% cheaper.
              Such as the Aoyue 474A++ that is only $145
              (+ 45.44 Shipping & 38.58 Importing). Or the Aoyue 701A++
              that costs $185 (+ 47.18 Shipping & $ 46.93 Importing).

              Only some sellers like from Israel sell Hakko's
              cheap at $140 for a complete Hakko 707. (excl. Shipping and Import).


  11. Humberto

    November 11, 2015 at 11:58 pm

    Hi Albert, the MJ13007 is a versatil transistor for
    SMPS and for more switching applications, it's very
    used for many techs. and repair persons in my country.

    Congrats. and keep up.

    • Albert van Bemmelen

      November 12, 2015 at 6:21 pm

      Hi Humberto. Where do you buy these MJE13007 Power Transistors
      while living in Cuba? Also on Ebay? Or can you directly
      order them from the United States? Because I noticed
      that prices had gone up while buying them on Ebay compared
      to about 8 months earlier.

  12. Ulises Aguilar Pazzani

    November 12, 2015 at 9:27 am

    Great job Mr Bemmelen

    • Albert van Bemmelen

      November 12, 2015 at 6:42 pm

      Thank you Mr.Ulises. Repairing SMPS, or ATX PC
      Power Supplies is fun. But I still have a couple
      of them that still are defect and more
      costly to repair. Because they have special
      PFC/PWM intergrated circuits
      (for instance the SOP-16: AN 4800) plus a special primary
      PWM switching circuit in a 8 dip IC (for instance a TNY 277PN).
      And the latter has probably a defect Mosfet integrated in the
      8 Dip IC why the Power Supply now doesn't work. And replacing
      both will be more difficult if they aren't available.
      By-the-way: Intel introduced this FormFactor in the year 1995.
      See this PDF file:
      or download read this link that explains some of the
      theory behind it:

  13. reza

    November 13, 2015 at 3:13 am

    hi Albert van Bemmelen
    thank u .

  14. Albert van Bemmelen

    November 14, 2015 at 10:23 pm

    This link also gives very interesting information about the new
    Low Start-Up current PFC/PWM Controllers in some new SMPSs. Like
    the in above Post mentioned AN4800 PFC/PWM controller which in
    fact is a FAN4800 chip. See this Fairchild link:
    This technique used makes it a bit harder to understand what is
    going on in any defective supply that uses such a controller.
    Which means that we probably also need to examine the datasheet
    of the AN4800 or any other PFC/PWM controller to be able to fix
    those defect Power Supplies that use these parts.

  15. Albert van Bemmelen

    November 15, 2015 at 6:37 pm

    More on the Basics on PFC (Power Factor Reduction), which can be
    defined as the reduction of the harmonic content to minimize the
    input current distortion, can be read on in this PDF:
    This also improves the Power Factor to be equal to 1
    (when cos phi 0 degrees = 1). So Input Current and Voltage are in
    Phase. After all Power (Watt) = Voltage x Current x cos phi.

  16. Raju varghese

    November 19, 2015 at 3:59 pm

    Hi Albert, good and valuable information thank you for sharing

  17. majid

    November 30, 2015 at 3:34 am

    Thank you

  18. Lad

    August 19, 2016 at 4:27 am

    Hi ALbert,
    Thank you for your great articles about reparing. As I could see you use more transistor testers.Can you please recommend one(best) tester for me?
    Thank you


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