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6 Bad Components Found In Dual Output Power Supply

By on September 27, 2019
power supply repair











A guy who works with my brother in a medical company brought me this power supply for repair. It was completely dead and it needed urgent repair.

power supply repair

If you look to the model number you will see that this dead power supply has two outputs; 12 at 2 amps and 30 at 5 amps ratings.

power supply repairing

As I took the screws off this device and uncovered the inside board, I immediately saw the damage.

It was water damage issue and a lot of parts already have been shorted and actually seen on board.

uc3842 ic board

When I saw this I had a chat with the customer about the repair and suggested to buy a new one since they are cheap and easy to find. At least that is what I had in mind but checking for such power supply that has dual outputs was not an easy thing to find except on the net.

The device was urgently needed and waiting for almost 22 days for the new power to arrive is out of the question.

burnt circuit board

That is the other side of the board and as you can see, the damage is huge and needed a lot of work.

burnt circuit board in power supply

bad components in power supply

The main fuse was open and therefore the bridge rectifier was shorted along with the Mosfet with part number 9N90C and the power IC with part number UC3842B. You may click on the datasheet photos below to access the website:

fqa9n90c datashheet

uc3842 datasheet

A fuse resister was open and the small burnt resister after searching on the net, I came to a conclusion that it was a 1k ohm.

burnt circuit track

I had to fix the connections on the printed circuit as well and make sure that it was clean from any water damage marks and then I installed the entire new components back on board.

dual power supply repair

The 12 and the 30 volts DC were present and steady.

dual power supply fix

Mission Accomplished.

This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.

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Note: You can check his previous repair articles in the link below:




  1. Albert van Bemmelen

    September 27, 2019 at 11:49 pm

    Quick pro repair! These power supply units indeed are very cheap when ordered through Aliexpress. In my case it only took 10 days for the unit to arrive.

    • Waleed Rishmawi

      September 28, 2019 at 4:04 pm

      Albert: yes they are cheap but the customer was not willing to wait.

  2. Parasuraman S

    September 28, 2019 at 8:56 am

    Good job! Very professional and thorough as usual!

  3. Waleed Rishmawi

    September 28, 2019 at 4:06 pm

    Parasuraman: thanks man. I appreciate it very much

  4. Henrique J. G. Ulbrich

    September 29, 2019 at 9:27 pm

    What seemed to point to a heavy work turned indeed to be a fast work. Relevant in this case your experience. Greetings!

    • Waleed Rishmawi

      October 3, 2019 at 2:09 am

      Henrique: it was fun to work in it and happy to see it come alive.

  5. Donald mwanza

    October 2, 2019 at 4:30 pm

    Water damaged electronics don't give me a peace of mind.
    The chances of it misbehaving are high

    • Waleed Rishmawi

      October 3, 2019 at 2:11 am

      Donalds: me neither but this device was not that bad water damaged.

  6. Yogesh Panchal

    October 12, 2019 at 11:31 pm

    Good Repair Waleed.

  7. Justice

    September 15, 2020 at 6:24 pm

    Late response due to covid -19. Now I am back on business. Good work Walleed , interesting outputs.


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