Don't Miss

Servicing Mercury SMPS  KOB AP4400XA

By on February 28, 2019
bulged filter capacitor









atx power supply repair

This SMPS was brought in a dead condition. As usual, opened it and cleaned the inside. The computer SMPS is always a haven for dust and moisturized fine dust and it takes a lot of time and might need a lot of efforts to do a thorough cleaning. Especially, the dirt and fine dust get amalgamated with the SMPS fan, and getting it cleaned is very, very difficult. We may have to use different kinds of brushes, including the bottle cleaner brush small and large.

This was a case of dry solder, yet other common faults in this continuously working unit of a computer. The Electrolytic capacitors were also out of range both in its value as well as ESR. So, replaced all the capacitors and patched up dry solders. Following pictures show you PCB, before dry solder patch up and afterwards, the board after cleaning etc. You can see that the board looks very clean and new! Not only do I clean the wires at its base in the unit, but also look for any wear and tear in it.

atx board repair


atx board repairing

how to fix atx power supply

The SMPS was working perfectly. I had also opened the cleaned and lubricated the SMPS fan. The grease inside the fan becomes hard and sticky and needs lubrication by WD-40. To open the fan, we need to peel off the sticker from its center and spray a very controlled spray of WD-40. In fact, the used high voltage transformer oil is the best for lubrication. It not only serves as a lubricant, but also cools off. In fact, the best lubricant for carbon potentiometers too! Even the noise due to stubborn dirt and dust particles stuck to the carbon track will get cleaned by using this!

Here is the SMPS checked for its proper function, fit back and tested once again, along with a picture of components replaced.

how to repair atx power supply

how to fix and repair atx power supplies

The satisfaction list bulged further!

This article was prepared for you by Parasuraman Subramanian from India. He is 69 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.

Please give a support by clicking  on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.

P.S-If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!

You may check on his previous repair article below:




  1. Albert van Bemmelen

    February 28, 2019 at 3:06 pm

    You take any repair including cleaning them very serious. And always with good result! I can't say the same at the moment because occasionally my defect desktop smps units are completely working but for instance only the Fan doesn't work. Maybe I now also need to replace 15 e-caps first (LOL)?
    In such cases a schematic of these units would be a great help but never can be found of course.

  2. Roger Wellesley-Smith

    March 1, 2019 at 5:29 am

    Please note, WD40 is definitely NOT a lubricant.

    WD40 is a dewatering and cleaning agent; but it quickly evaporates; leaving virtually no residue.

    I am not criticizing your use of WD40 as you have stated; nor that it worked; it just needs to be made clear that WD40 is not a lubricant that can have anything other than a short-term effect.

    • Parasuraman S

      March 1, 2019 at 12:29 pm

      Of-course. I agree with you and am aware of it too. There is already grease inside every SMPS Fan. It gets hardened. What we do is spray the WD40, not only to lubricate it temporarily, but also soften the grease, which remains so for a long time afterwards, from my experience. Kindly refer to book on SMPS/ATS repair by Jestine Yong. He has also suggested use of it, like many other postings in the website. WD40 even clean potentiometer and such other controls, without leaving any residue. From my experience, it does not dry fully, as I keep a sprayed WD40 inside an open cap for immediate local lubrication. It contains kerosene and oil. It remains like that for many days without evaporation of its oil. If you want, try it and see. Anyhow, many thanks for your observation and feedback!

      • Robert Calk Jr.

        March 8, 2019 at 1:10 pm

        Hi Parasuraman. I could not find it in any of Mr. Yong's books where he advises mixing WD-40 with old nasty hard grease. Do you know what page it is on?

    • Robert Calk Jr.

      March 1, 2019 at 3:52 pm

      Why anyone would use wd-40 to lubricate a fan instead of a dab of grease is a complete mystery to me.

      • Parasuraman S

        March 2, 2019 at 12:52 am

        The reason is adding more grease might not get properly mixed with hardened grease already there. Whereas WD40 penetrates and loosens that bond. You can add a little grease afterwards. The method employed by me is spraying WD40 while rotating the fan by hand. That's what gets good result.

        • Robert Calk Jr.

          March 2, 2019 at 10:09 am

          A dab of grease barely costs anything. I just remove the old grease with some alcohol, add a dab of new grease, and be done with it.

          • Parasuraman S

            March 3, 2019 at 5:51 pm

            It depends on availability of the type of grease used in the fan. Such grease is not available in electronic shops here in this area. I have been using WD40 for quite some years. I have found its use very good and no complaints received afterwards. Perhaps, the formula used here might be different!

            • Robert Calk Jr.

              March 4, 2019 at 5:20 pm

              A decent quality lithium grease should work. I use white lithium grease by Permatex, nothing special. I am on my laptop several hours a day and the fans in my Targus Chill Mat that I serviced are still running great and whisper quiet.

              • Humberto

                March 6, 2019 at 10:51 pm

                WD-40 is dielectric too, a good feature in my opinion

                • Robert Calk Jr.

                  March 7, 2019 at 1:38 pm

                  All you have to do is google it and nearly every article says that WD40 is not a good lubricant. Even Popular Mechanics dispels the myth. It has some good uses but lubrication is not one of them.

  3. Bob Lamparter

    March 3, 2019 at 4:29 am

    I'm also in the do not use WD-40 camp. Unless WD-40 is formulated differently in SE Asia than it is in the USA, it will leave a varnish like residue and dry out over time. A very good and inexpensive lubricant is automatic transmission fluid.

    • KYBOSH

      July 25, 2019 at 2:15 am

      Wow...ATF??? That's the first Ive heard of that one.
      Anything, other than personal experience, to back this claim up?
      (Trust but verify)

  4. Humberto

    March 6, 2019 at 10:53 pm

    Great repair Parasuraman. Mr. Jestine Yong sells a great e-book about repairing SMPS, including PCs SMPS.


Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.