Badly Burnt Varistor In Control Board

By on March 14, 2018
series light bulb tricks











A guy next door, who deals with installing gate motors, came to my shop and he had a board in his hands. The moment he entered the shop, I could smell burned plastic. I had no idea what the problem was. He asked me to repair it as soon as possible so he can install it back.

door electronic control repair

Here is the board but I guess it is too dark to see the exploded component on that board.

I took the component off the board and it was really damaged. Take a look

burnt varistor

It was a part found in the primary section of the power supply and it is called the Varistor. I had to do with the in rush current in the device. Its main function is to protect the device from further damage if the device was exposed to higher voltage/current.

bad varistor

The moment I took this part off board, I could not see any further damage to the board. I could not find the part number on it. I just replaced it with another one from a similar board.

I could see a dark resistor next to the blown part, I thought it was damaged but I after cleaning with alcohol, I could see it was in good working conditions.

I replaced the blown varistor and before I connected it to power, I took the fuse off which was already blown and installed a light bulb to check if there still short on board.

series light bulb trick

Powering the device with light bulb connected to the fuse terminals proved that this device is function the way it should be, because if there was still short on board, the light bulb will come on bright and stay bright. In this case, the light bulb did not even come one and that is excellent.

how to repair door electronic control board

As you can see, the board is working fine. I replaced the blown fuse. It worked like charm. 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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  1. George Greenfield

    March 14, 2018 at 9:56 pm

    I've seen Varistors in a similar state myself. Looks like it did its job and protected the rest of the circuitry. Good job Waleed !


  2. Andrew F. Ali

    March 14, 2018 at 11:28 pm

    Great work. The varistor did its job. Well done.

  3. Suranga Electronics

    March 15, 2018 at 12:43 am

    Very Good.

  4. Parasuraman

    March 15, 2018 at 9:10 am

    A true warrior who killed himself to save others! Its the Commander who found him and replaced it! Well a good restoration indeed!

  5. Robert Calk

    March 15, 2018 at 11:36 am

    Good job, Waleed. I'm glad it worked, even though charms do not. lol

  6. Ulises Aguilar

    March 15, 2018 at 12:32 pm

    nice job

  7. Waleed Rishmawi

    March 15, 2018 at 2:08 pm

    Parasuraman: I never heard it put that way but thanks. I appreciate the support and the encouragement. have a blessed day

  8. Albert van Bemmelen

    March 15, 2018 at 8:16 pm

    Good job! You probably also wrote down the correct varistor value from the other one you took from a similar board. In case you run out of similar boards in the near future?

    • Waleed Rishmawi

      March 16, 2018 at 6:21 pm

      Albert: no I did not since they are easily found and always available.

  9. Yogesh Panchal

    March 15, 2018 at 10:26 pm

    Good Job ! Waleed.


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