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An Air Condition Power Board Repair

By on August 28, 2020
how to repair air cond power board









An AC technician brought his board for repair and explained that it was a dead one. As I powered up the device, I did not see any sign of life on that board.

how to fix air condition board

As you can see, it is a very clean board and when checking with my naked eye for any fault, none was found.

The main fuse was intact.

how to repair air cond power board

That is the other side of this board and I could not see anything wrong there either.

As I checked for voltage reading at the main capacitor, there was no reading there. From a logical point of view the best way to trace the problem is go backwards from that point on and find my voltage reading that is missing.

how to fix and repair air condition power board

If you check on the board you will see that the main voltages come from that transformer but when I checked the output of that transformer, there was no reading either. When I checked the power on the input of that transformer there was 220 present.

Yes, you got that right, the transformer is faulty. It was getting the 220 volts from the main line but there was no output.

faulty air cond linear transformer

That is the specs of this transformer. I should be getting 14 VAC and 11.5 VAC on the output. If you look to the main input of this transformer, you will see a fuse and I bet that fuse was open causing this board not to function.

bad internal thermal fuse in linear transformer

With a fine tip blade and sharp eyes, I was able to open the transformer from the input side looking for that fuse and I found it. As expected, the fuse was open and needed a replacement. It is a very delicate wires that I am dealing with here so be careful when doing such a repair. I could get another transformer and just install it but where is the fun in that?

I managed to replace that open fuse with a good one and plugged it back on board and powered up the device.

how to fix bad transformer in air condition

As you can see, the green light came on indication a successful repair and to that I can call it…

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. Yogesh Panchal

    August 28, 2020 at 9:10 pm

    Good Job! waleed
    Similar thermal fuse i found in many AC adapters Specially in Speaker system.

    • Waleed Rishmawi

      August 28, 2020 at 10:56 pm

      Yogesh: yes you are right. The hint here is to replace with the same kind of fuse.


    August 28, 2020 at 9:36 pm

    qual a especificação do fusível trocado

    what is the specification of the replaced fuse

    • Waleed Rishmawi

      August 29, 2020 at 1:30 pm

      ADIRSON: I am not really sure but I think it was 3.15 amp. the idea is no matter what the ratings are you need to replace it with the same specs fuse. have a blessed day

  3. Parasuraman S

    August 28, 2020 at 9:47 pm

    Good investigative remedy there! Both the Transformer manufacturer and the dealers would feel envy after seeing this! A job well done!

    • Waleed Rishmawi

      August 29, 2020 at 12:23 am

      Parasuraman: I really enjoyed this repair very much. You put a smile on my face.

  4. Albert van Bemmelen

    August 28, 2020 at 11:54 pm

    Replacing thermal fuses is okay as long as we can be sure that using the this way 'repaired' old overheated transformer doesn't cause our house to go up in flames.

    • Waleed Rishmawi

      August 29, 2020 at 1:34 pm

      Albert: caution was well taken before installing and isolating the fuse. i have been doing this for a long time but so far I have not experienced a house go into flames. I do this process only if I can not find a replacement for that transformer otherwise I would replace the faulty with a brand new one. have a blessed day

  5. Henrique J. G. Ulbrich

    August 29, 2020 at 5:47 am

    Good job, Waleed. I´ve dealt with a multi-channel soundboard that revealed trouble with one of the two power transformers. The same issue: a thermal fuse inside the transformer. However, it was not possible (nor so easy as in your case) to get access to the thermal fuse at the risk of destroying the transformer. The solution was to replace the transformer.

    • Waleed Rishmawi

      August 29, 2020 at 1:39 pm

      Henrique: thanks man. indeed, there are lots of fine wires to deal with and it is not an easy repair to do. it was not any easy repair for me but it was challenging one. of course I only do this process only if I do not have a replacement or I try to open the transformer and mess it up instead of fixing it. lol. have a blessed day


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