Not Common To See Dual Super Barrier Rectifier Breakdown When Under Load

By on May 30, 2016



led tv no power

 

 

 

 

 

 

 

 

 

bg led tv repair

The complaint of this LED TV was no power so the first thing I did was to check the output voltage of the power adapter.




It was rated as 12 VDC and when I measured the output jack  of the power adapter I got 12.1 volt which mean it was good -see the photo below:

testing power adapter outputSince the power adapter was checked to be good, I had to open the TV to perform further test.
open led tv

When i checked on the connector of the dc 12 volt supply in the circuit board I was surprised to see the voltage was only 3.6 volt. It suppose to be 12 vdc and not 3.6 volt.

testing led driver circuit

This means the problem can be caused by either the circuit board itself or the power adapter. In order to confirm which section is giving the problem i have used an external 12 vdc to plug on the circuit board-see the photo below:

12 volt power adapter

It shows 12 vdc and I could see that the LED TV screen was working (see below photo). This concluded that the power adapter is the cause of the problem. It also means that the power supply can’t sustain the current draw by the circuit board causing the 12 volt to decrease to 3.6 volt!

led tv tested ok

Next, I opened the power adapter and see if I can find some bad components in it. The filter capacitors were checked to be good and there were no sign of burn components too. All components were intact.

repair led power adapter

Even the dual schottky diodes was tested good when checked with my digital multimeter

testing schottky diode

 

Below is the Dual Super Barrier Recctifier datasheet:

sbr20100ct datasheet

Since I could not find any bad components in the power supply, I directly replaced the dual super barrier rectifier and retested it again. I was a bit surprised to see the voltage came back to normal again (11.6 volt) and the display appeared-see the photo below. It had never came to my mind that a dual diodes could breakdown when under load.

power adapter tested good

 

led tv no power repair

Conclusion- Sometimes one just has to direct replace a component and retest the set because a component that is breaking down when under load is hard to be detected by a normal meters.

All the best!

 

suranga

This article was prepared for you by Suranga Bandara who owns an Electronics shop in Anuradapura, Sri Lanka.

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Note: You may check out his previous repair article in the below link:

http://www.jestineyong.com/singer-dvd-player-tray-cant-fully-open/

 

 

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17 Comments

  1. Parasuraman S

    May 30, 2016 at 10:26 pm

    Great! Yes, that is something new to me too!

    Likes(2)Dislikes(0)
  2. Kybosh

    May 30, 2016 at 11:19 pm

    Great read. Very smart of you testing with an external power supply.

    Likes(1)Dislikes(0)
    • Francis Fernandes, Mumbai, India

      June 17, 2016 at 9:30 pm

      Mr Bandara,
      Great work. I wonder if you could comment on a similar problem I had with the SMPS power supply of a DVD player. There is a 8 pin DIL ic which I think is the oscillator (no.4SY103) which I feel is the problem as the set is dead and there is no output 12volts. I need to know the data of this IC but could not find it on the net. If you could throw some light I would be grateful.

      Likes(0)Dislikes(0)
  3. Humberto

    May 31, 2016 at 12:18 am

    Wow! Suranga what an unusual case! Thanks for sharing your expertises.

    Likes(4)Dislikes(0)
  4. Anthony

    May 31, 2016 at 11:49 am

    Good repair Suranga, there's always something new to be discovered when repairing electronic equipment and we must always try to think outside the square when we run into dead ends....Thanks for sharing your repairs here.

    Cheers

    Likes(3)Dislikes(0)
  5. beh

    May 31, 2016 at 7:02 pm

    yes .this shows that our knowledge in testing the electronic component is not enough BUT the ex prince is telling the last word thanks SURANGA for this repair report it is super .

    Likes(3)Dislikes(0)
  6. Mason

    May 31, 2016 at 8:52 pm

    Nice find, way to stay after it.
    Thank you,
    Mason

    Likes(1)Dislikes(0)
  7. Robert Calk

    May 31, 2016 at 11:48 pm

    Good job finding the culprit, Suranga.

    Likes(1)Dislikes(0)
  8. Henrique Jorge Guimarães Ulbrich

    June 1, 2016 at 12:45 am

    Great, Suranga. I'd never found such an interesting problem yet. Every day is a day to learn something more. Thanks for the share.

    Likes(1)Dislikes(0)
  9. albert van bemmelen

    June 1, 2016 at 5:43 am

    Thank you Suranga! This shows that it is so much harder to repair something that behaves erratic than something that doesn't work at all!

    Likes(2)Dislikes(0)
  10. suranga bandara, Suranga Electronics

    June 1, 2016 at 7:47 pm

    Hi All my Friend,
    Thanks so much for your feedback.

    Likes(0)Dislikes(0)
  11. skwong

    June 2, 2016 at 6:43 pm

    From my experience SMPS power supply has to be tested with load. Normally, I use a bulb rating close to the measured voltage.

    Likes(0)Dislikes(0)
  12. Chris

    June 3, 2016 at 6:22 am

    Thank's for the interesting article.
    In the past of time, I repaired a led brake light on a VW Golf 5. They have some load's in the circuit because the car ECU will alarm a bad bulb if the load is not connected but only the led's.
    So, there was some diodes too. The behavior was sometime working brake light and some time not working. I changed and tested all the stuff and the diodes was good on the multi meter. I decide to change the diode's. BanG! the brake light is still working, after 2 years or so...
    When I tested the diode under load, she failed. The diode was shorted, without a load she was fine.
    I never figured out why the diode had that behavior but it was so.
    Thanks for sharing, and keep up with the interesting articles.

    Likes(1)Dislikes(0)
    • Robert Calk

      June 4, 2016 at 6:05 am

      Hi Chris,
      That's why Mr. Yong recommends checking the diodes with an analog VOM that has the 10K, which includes the 9V battery. The 9V battery plus the 2 AA's will have about 12V to check with on the 10K setting. I don't even waste my time checking them with a DMM.

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  13. Yogesh Panchal

    June 3, 2016 at 4:29 pm

    Suranga,

    What lead you towards this diode failure doubt; are surrounding voltages??.

    Likes(0)Dislikes(0)
  14. justice cele

    June 6, 2016 at 9:26 pm

    Suranga great job thanks for sharing such vital knowledge.

    Likes(0)Dislikes(0)
  15. sylvester

    June 7, 2016 at 7:12 pm

    Did you try testing with an analoug meter set to x-10, since its only a 12v power supply?

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