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PC ATX PSU Quick Repair

By on September 1, 2015
atx power supply repair








In this document, I show you a repair article with high voltage sources. If you are not familiar with high voltage and or you have not the right tools, please do not repair this type of units. High voltage can damage your health even end in death.

atx power supply repair

Today a call comes down on my phone line from an accounting agency with a serious problem on their server PC where the databases of the customers are stored. The PC could not start and the other client computers could not work in the office because of no server problem. I moved immediately to the agency to see what is the problem and what is to do.

The server is a PC P4 with XP and with an MS SQL server installed on. Not a big deal but it does the job. In a few second I got the ride with the problem of the PSU, figured out does the PSU is bad. The agency has no other PSU for situation like this so I have to order one. However, it will take a day or so before it arrive. I decide to repair the PSU.

First, I checked for the version number of the PSU. This PSU is a Version 2.3 as you can see on the photo right in the table of DC OUTPUT MAX. These version numbers describe the typical construction of the PSU, which is an international regulation, and must fit the mechanical and electrical standards.

Here is a revision history of the PSU versions: 

Version Release Date Notes

1.0 Dec, 1997 Public release

1.1 Apr, 1998

  • Updated all mechanical outlines to clean up dimensioning of mounting holes.
  • Added chassis cutouts for all mechanical outlines to clarify keep-out areas.
  • Added Appendix C. 2.0 May, 2001
  • Added SFX12V description
  • Additional power ratings added
  • Updated industry standards
  • Increased standby current

2.1 Aug, 2001

  • Section 4.4 Updated Figure 4 SFX/SFX12V Connectors
  • Section 5.8 removed vendor name 2.2 Dec, 2001
  • Section 3.23 Typical Power Distribution. Change minimum loading on 5V rail to 0.3A
  • Section 3.3.2 PS_ON#. Add text “The power supply should not latch into a shutdown

state when PS_ON# is driven active by pulses between 10ms to 100ms during the decay of the power rails.”

2.3 April, 2003

  • Reformat and update revision table
  • Update Disclaimers
  • Remove guidelines for SFX without 12V connector
  • Updated power and current guidance
  • Added efficiency targets for light and typical loading
  • Increased minimum Efficiency at full load from 68% to 70%
  • Updated guidance for standby efficiency
  • Added Serial ATA connector
  • Updated cross regulation graphs

This is ver.2.3 PSU, there are no big differences what the electronic stuff means.

My second and very minimalistic test was to disconnect the PSU from the motherboard and from all other devices, shorted the GREEN and BLACK wire wit a wire. The PSU started up immediately.

I was a bit surprised! I expected does the PSU will not power up, but…

After this test, I connected my Xilence PSU tester to the unit and see what is happening:

atx power supply tester

In real world, this type of testing is nothing than checking the voltages and the PG time. This type of tester are failed in lot of situation and do not detected a bad PSU even when a load is added on the PSU or without that. In other words, it is just a multi meter which can show all the voltages and the PG time on one screen on the same time. Do not expect too much from this tool.

Can you recognize the problem? Yes? ok, No? no problem. Check the zoomed picture of my tester. You can see four different voltages and one so called PG in ms.

Voltage 1: +3.3V

Voltage 2: +5V

Voltage 3: +12V

Voltage 4: -12V

The PG is the Power Good signal, which is measured in milliseconds or ms. Every PSU have a DC Voltage regulation, which shall remain within the regulation range. With or, without loads on the output connectors.

This is the DC output Voltage tolerance. 

Here I made for you a DC output tolerance table, which you can use for almost every ATX PSU for PC computers. In most case, I use the reference guide made by Intel.

atx power supply repair3

I got a measurement on my PSU tester on the 5VSB between 3.9v – 4.5v. This is outside of the tolerance table and makes the mistake. +5 VSB is a standby supply output that is active whenever the AC power is present.

This output provides a power source for circuits that must remain operational when the five main DC output rails are in a disabled state. Example uses include soft power control, Wake on LAN, wake-on-modem, intrusion detection, or suspend state activities.

Today’s modern motherboard has a so-called logic controlled power up circuit. Therefore, the power button is connected to the motherboard and not to the PSU as it was on the old type of PC-s. Because of this logic control circuit the PC can’t power on but without the mobo the PSU powered on when I shorted the green and the black wire on the PSU connector which goes to the motherboard. The next very important element to trouble shooting is the PG parameter.

The Power Good or by Intel PWR_OK is a signal used by the system power supply to indicate that the +5VDC, +3.3 VDC and +12VDC outputs are within the regulation thresholds of the power supply. If the PG signal timing is between 100ms and 500ms the PSU should be fine otherwise the PSU have some problems. As I realized does the 5VBS are in a bad range, the PG signal is in range with the other voltages I was sure does there is not a big problem. Lets see what was the problem:

power good problem

Inside of the PSU. A bit dirty but nothing unusually or? I recognized a slightly swelled capacitor. I took my good old ESR meter, which is a homemade one and checked all the caps and this one too. After the checking of the caps, there was only one cap out of the range. This bulged one.

atx power supply repair6

Here is the reading, LOŠ means BAD.

analogue esr meter

After this, I checked for shortened components or faulty one but nothing else was found. There was another small problem. A grinding noise, come out from the cooling fan unit of the PSU. After I disassembled the fan, and add some graphite grease, the grinding noise was gone. See the pictures below.

atx power supply fan repair

atx power supply repair9

Cleaned the whole unit with compressed air and assembled it together. Here is the result:

atx power supply checker

After I put the PSU back to the server, it powered on and worked well.

You can find great ATX PSU repair guide from Mr. Jestine Yong on this web site: if you interested to learn how to repair these kind of equipments.


I use this technique to quickly identify the place or path of the problems in these kinds of units.

– short the green and any black wires on the connector when the PSU is out of the PC

– if PSU starts than you have no big problem

– if you have a PSU tester something like mine use them to measure the voltages and PG, if

not then use a usually multi meter

– check the results with the voltages output reference table from this article

– identify the faulty voltage and start checking the parts in that area

This article is for basic skilled repairer and novices in the world of PSU repairing.

For further learning of the technique of repairing PSU equipments please refer to the books by Mr. Jestine Yong who made a well explained repairing guides with great pictures and explanations.

I hope you will enjoy this article.



This article was prepared for you by Christian Robert Adzic from Novi Knezevac-Serbia.


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Note: You can check his previous post in the below link:




  1. Anwar Shiekh

    September 1, 2015 at 9:12 pm

    Very impressed with your homemade ESR meter; any chance of an article on its design and construction?

    • Chris

      September 2, 2015 at 12:58 am

      Thanks folks for the comments about the ESR meter. 🙂
      Huh! it was many years ago when I made this think, I will see if I can find the schematic and I will maybe write an article about.
      But! there is a nice ESR meter meter on this site, the Blue ESR meter. Maybe it didn't worth to made one today.
      I don't know. I like to make stuff by me. It is relaxing me and all the time I learn new thinks or practice the old one...

      • Zed Pato

        September 2, 2015 at 1:57 pm

        Sir Christian Robert Adzic try to share your schematic diagram of your esr Thanks. The scale is up to 200 does it reall can read 200 ohms sir. THANKS FOR YOUR REPAIR INFO. Are you the one who design that esr meter sir. I am interested to make one even i have blue esr. God bless

        • Chris

          September 3, 2015 at 3:07 pm

          Zed Pato: Thank you for supporting my article. Today I tested the ESR meter with a resistor of 200 Ohm and it measured that resistance.
          I newer come to the idea to test this before. Thanks for the idea.
          I got the circuit from an electronic news paper many years ago.
          I will search if I have somewhere that, and will share if the rules of this blog are agree with that. If I found the schematic, I will contact the administrator of this blog and see what he will say.

          • Zed Pato

            September 5, 2015 at 4:00 pm

            thank you sir and we will wait for that article. I know sir jestine will authorized you because he loves to shareelectronics information. I am rigth sir jestine? Cheers!!!

            • Zed Pato

              September 5, 2015 at 4:45 pm

              may be u can share also the esr printable scale and pcd design sir if you have thank you so much

  2. Merlin Marquardt

    September 1, 2015 at 9:31 pm

    Very good.

  3. albert

    September 1, 2015 at 10:23 pm

    Excellent job..

  4. Mayank Tyagi

    September 1, 2015 at 10:41 pm

    i m ur big fen sir, i like ur all artical they r very helpful for me a learn a lot of thing by ur artical.
    Thanks a lot thank u very much sir.

    • Chris

      September 3, 2015 at 3:24 pm

      Mayank Tyagi:
      Thank you very much for your comment.
      I appreciate it and I like if my articles can be used by the readers, otherwise they would be non-sense.
      For me the most valuable in an article is if I can learn something new from it.

  5. Christopher Massie

    September 1, 2015 at 10:41 pm

    A very well-written Article. Clear and detailed explanation. Thank you for the basic theory behind the PC P/S. Excellent workmanship and logic flow.
    I hope you will write more articles Mr. Adzic!
    Thank you.
    Dobre Dan,

  6. Yogesh Panchal

    September 1, 2015 at 11:02 pm

    informative explaination thanks for sharing.

  7. Humberto

    September 2, 2015 at 12:13 am

    Congratulations Chris, a good tutorial and nice photos.

  8. Robert Calk

    September 2, 2015 at 12:29 am

    Good job, Chris. Thanks for the well written article.

  9. Mark

    September 2, 2015 at 5:16 am

    Hey Christian,

    Thanks for the very clear step by step article. The details made it very clear in finding the fault. Where are you able to get this data from? I have trouble finding some information when I am doing electronic repairs, which makes the job twice as hard.

    Thanks for sharing!

  10. Chuba

    September 2, 2015 at 1:08 pm

    Very Good article, and hope for more articles in the future.

  11. S Ramachandran

    September 2, 2015 at 1:24 pm

    very nice article and clean way of description on repairs. good work keep it up.

  12. reza

    September 2, 2015 at 7:27 pm

    hi Christian Robert Adzic
    thank u .

  13. Albert Hoekman, Holland

    September 3, 2015 at 5:41 am

    Hi Mr.Chris, the first thing I saw at the PSU tester is the 5 Volt Stand By voltage, this should be minimal 5% + -. This is needed by the motherboard to start up when the PC is switched off. In your case it is 4,4 Volts which is too low and therefore the motherboard did not start and there was of course no Power Good signal from the motherboard. Of course the problem was the bulged E-cap.
    Thanks for the article, very good explanation too.

    • Chris

      September 3, 2015 at 3:36 pm

      I appreciate you support my article.
      You are right with the explanation.
      Thank you for supporting.

  14. Osman AL Sinnary

    September 4, 2015 at 7:08 pm

    Good work , Nice way

  15. Mohammed Kasim

    September 6, 2015 at 5:46 pm

    Very good information. Nice ESR meter. Plz post an article on how to make one

  16. Debirt

    September 8, 2015 at 9:28 am

    Keep the good work up. It is always good to logically follow the process.

  17. dondonis

    September 8, 2015 at 8:19 pm

    thank you Sir for sharing. Very informative and clear. The psu tester is a great tool for quick checking and i hope to get one.

  18. Chris

    September 9, 2015 at 5:59 am

    Ok folks, if you can read this comment than you have lucky, because Mr. Jesting was shared the whole source of a similar ESR meter as I build years ago and I use now days too.
    Here on this link you can get all the stuff you need to build the ESR meter like mine, it is not the 100% same but very similar.
    Good luck on building and let as know about the progress. 🙂
    Here is the link:

  19. Ulises Aguilar Pazzani

    November 12, 2015 at 9:45 am

    good job Sir

  20. Ulises Aguilar Pazzani

    December 9, 2015 at 10:25 am

    Mr Robert a very nice explain Job , I like Your home make ESR meter , like readding Your artcles

  21. Christopher Massie

    February 24, 2016 at 9:33 am

    Great article Christian. this is the type of logical step-by-step detail I wish all articles would have. Very good detail and pictures!
    Thank you sir. You are a Master Technician!!

  22. Bob Greene

    November 4, 2018 at 1:13 pm

    Chris, in the server PSU, you detected an out-of-range 5vSB line and a bulged capacitor. Yet, nowhere-- at least, not in the sequence of your diagnosis-- do you indicate that you actually replaced the bulging capacitor.

    Quite properly, you lubricated the fan, since a fan failure invites equipment overheating and failure, but the capacitor remains a problem

    You also did not explain whether an out-0f-range 5vSB line can be expected to cause further failures-to-start with the server.


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