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One Zener Diode Found Cracked And Another Shorted In CCTV SMPS

By on January 22, 2020
6v2 zener diode










atx power supply repair

This 12V SMPS of a CCTV Camera was given to me by my technician friend, stating that it was reported to be dead. I brought it home and subjected it to thorough cleaning inside and outside. The cover was already open and was not having its screws.

As I noticed a lot of dry solder on the board, I cleaned it first and carried out retouching all the solder joints fresh and cleaned it again.

clean power supply

Applied power and noticed that there was no output.

tl494cn ic atx

atx repair and fix

So, disconnected and discharged the tank capacitors. Carried out ESR checking of caps and Ring testing of Transformer both of which got passed. Then I checked each and every component on the board, first of which was all diodes. While checking, I noticed that one 13V Zener was short and another one next to it was found cracked.

The crack was not easily visible, and chanced to see it only when I pressed the probes at both ends for checking. Unfortunately, the value was on the two cracked pieces and I could not make it out. So, I used Fevibond and stuck the two pieces together exactly how it was and then read the value, it was 6V2 Zener.

6v2 zener diode bad

6v2 zener diode bad and faulty

6v2 cracked

Replaced both Zener diodes. Checked rest of the components and could not find anything else faulty. So, powered the SMPS through a series bulb like before. It worked very well, with its SMPS Fan whirring smoothly:

checking atx power supply

So, reassembled the board and rechecked it:

working atx power supply

recheck atx power supply

Another interesting troubleshooting completed satisfactorily, qualifying itself to jump into the bag!

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.

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  1. Albert van Bemmelen

    January 22, 2020 at 11:59 pm

    Using Fevibond and sticking the two broken diode pieces exactly together and reading the value of the 6V2 zener is brilliant especially if in this way it also was still measurable as a good zener. Similar to how most point contact diodes are manufactured and work.

  2. Mark

    January 23, 2020 at 5:41 am

    Well done Parasuraman,
    It was a good idea to glue the diode together to make it easier to identify!

    • Parasuraman S

      January 23, 2020 at 5:31 pm

      Thanks, Mark!

      • ralph

        July 29, 2020 at 6:57 am

        TL431 feedback may be failing so there was overvoltage and output protection zeners fail short to protect from overvoltage

  3. Waleed Rishmawi

    January 23, 2020 at 5:10 pm

    I love the gluing the zenner part for testing..I never done that before to know the value of the zenner. thanks for that new information. again,a job well done and keep up the good work. have a blessed day

  4. Parasuraman S

    January 23, 2020 at 5:30 pm

    Thanks, Albert! No, it is not possible to measure it, as the conductance cannot be ensured by this type of bonding.

  5. Justice (City of Durban --South Africa)

    January 23, 2020 at 7:59 pm

    Yeah Parasuraman, very unique approach--I have never thought gluing together of broken part, yes we learn till we stop breathing.Thank you so much for such an experience!!

    • Parasuraman S

      January 26, 2020 at 8:59 am

      Yes very true! Even when we die, we learn how to leave this body!

  6. Robert Calk Jr.

    January 24, 2020 at 3:10 pm

    Good job, Parasuraman!

    • Parasuraman S

      January 26, 2020 at 9:00 am

      Many thanks, Calk! All because of your continued support!


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