A technician in a medical company brought this power board for repair. While the technician in my workshop, I powered the board and I could hear a clicking noise coming from the relay. After few clicking noises, the clicking stopped and the power board was working fine.

power board repair

The clicking noise was coming from that area where it is marked with the red square. It made sense because there is only one relay on that board and it was easily identified.




When I got closer to the relay I found a big surprise. Take a look

relay burnt

The relay is located next to a resistor that is 47 ohm 5 watt. These kinds of resistors produce heat and it seems like it was very close to the relay that caused a big hole there. The relay was still working fine but it had to be replaced. I took the old relay out and replaced one with the same specification. It was 12 volts with 30 amps rating. I did not want the resistor to be close to the relay, so I extended the legs of the resistor to be higher than the relay itself keeping the heat away from that part.

relay bad

I powered on the device and to my surprise, the new relay that I just installed started clicking faster and never got to a point of stopping and the board failed to produce power. A relay that is clicking is due to the fact that the source of power to the pins of the coils is not steady and I believe it was a capacitor issue.




While I was checking the board, I came across few parts that needed replacement.

gme esr meter

This capacitor was open and it was replaced. I also found another capacitor that had to be replaced as well.

0.47uf 250 volt capacitor

Shockingly after replacing these faulty capacitors and powering up the board, the board worked fine for about few seconds and then, the entire board went into shut down. The relay was not clicking anymore but there was a sign of power on the power stand by light on the board.

zvn4206

That is the transistor that feeds 12 volts into the one of the pin of the relay. When I tested for voltages there, there was nothing. I took it off board and tested, it was shorted. The part number ZVN4206 and I replaced it with IRFZ20 which not an SMD transistor but it worked fine. Below are the specs of the transistor:

zvn4206a datasheet

IRFZ20 DATASHEET

irf220

I powered the device, the LED light on the other side of the board came on and the relay clicked once and everything seems to be working fine.

power board relay problem repair

Mission Accomplished.

waleed

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:

https://www.electronicsrepairfaq.com/a-deserted-calculator-printer-brought-back-to-life-model-casio-dr-t120

 

About

Jestine Yong works as an Electronics Repair Lecturer in Kuala Lumpur Malaysia and his training website is http://www.NoahtechElectronicsTraining.com. You can check out his repair blog at http://www.JestineYong.com

13 comments on “A Melted Relay and Clicking Noise On a Power Board Repaired

  1. Albert van Bemmelen says:

    Since both IRF220 and the ZVN4206 are N-channel mosfets and share about the same RDSon resistance in forward conducting mode, only fitting the not smd component in place was the last hurdle to take. Good job!

    1. Waleed Rishmawi says:

      Albert: thanks man. Plenty of space to fit the big part. It was no hassle.

      1. Harry says:

        hello waleed
        my name Harry from israel . i read the article very nice
        you lived at Bethlehem? my neighbors

        good luck friend

    2. Mokhtar Hassan says:

      Great job

    3. alfie peralta says:

      thanks so much for sharing .

      it saves a lot
      same time , additional nuggets.

  2. Parasuraman Subramanian says:

    Reading the article, I guessed it must be you, the sole authority on such trouble shooting methods! Great Job!

    1. Waleed Rishmawi says:

      Parasuraman: thanks. Have a blessed day.

  3. Willsgadi says:

    Thanks for effort I very humbled to receive, very helpful and educational. Hope you always me considered in af your successful work thanks A lot.take care of your self and your family always be healthy on this crisses of covid-19.

  4. Lewis Spedding says:

    Great work Waleed Thank you.
    I was interested in current circumstances of the Corona Virus that it was a piece of hospital equipment. Was it a laptop?
    I find myself rearching power supplies!
    Thank you

  5. Emmasoft says:

    Fablous! I hve a power adopter of flat tv set. . Out put capacitors keep deforming hve worked for several times now whenever you connect to tv become absolutely hot , hve failed to notice where it could hve gone wrong but jst keep replacing the two capacitors,. Sme advice please .Rem.the standby lite is also off .

  6. Joven Urbano says:

    Wow, that was a hard fix! Well done!

    1. Patrick says:

      Great job!

  7. Nice work sir very fine, congrats

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