Shorted SMD Transistor In LED TV

By on May 5, 2018
led tv mainboard repair

 

 

 

 

 

 

 

 

 

 

bg led tv repair

The complaint of this 23″ LED TV was no display but there was power (the power LED light was on). The sound was good too except no display. However, the TV LED backlights were On -see the photo below.




This means that the internal LED TV driver board was working fine.

no display in led tv

Once the cover was removed, I could see only two circuit boards i.e the main board and the backlight LED driver board.

led driver board for backlight

I then checked on the mainboard voltages to the LED Backlight driver board and found that the three dc voltages of 3.3 volt, 5 volt and 12 volt were present. You need to check these pins when the dc power jack is connected and is on.

led driver board for led backlight

Next, I checked on the 5 volt dc line to the TV panel and found that it was only 1.44 volt instead of 5 volt. I knew this is the main cause of the TV no display problem.

how to check led tv mainboard

I started to track from this 5 volt connector pin and found one suspicious SMD transistor where it received 5 volt but the output was only 1.44 volt.

shorted smd transistor in led tv board

I soldered out the SMD transistor and check it off board and true enough the transistor had a shorted leads where it showed 17  ohms. The ohms value should be high.how to test smd transistor

It is time to look for the spare part. I search from the junk board and found the right SMD transistor and soldered it-see the photos below:

testing smd transistor

After putting in the good SMD transistor and powered On, the 5 volt came back.




You can see the 5.09 volt reading from the meter in the photo below:

checking voltage in mainboard

The best moment was able to see the TV display came back and the satisfaction is beyond description.

no display in led tv repair

no display in led tv solved

Conclusion- It is possible to repair TV mainboard if you able to track or understand the circuit. If you wish to become a better TV repairer you can check out Kent’s and Damon’s ebooks.

suranga

 

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




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Likes(114)Dislikes(1)

16 Comments

  1. Robert Calk

    May 5, 2018 at 12:48 pm

    Good job, Suranga.

    Likes(3)Dislikes(0)
    • Suranga Electronics

      May 5, 2018 at 11:21 pm

      Thanks Mr.Robert

      Likes(1)Dislikes(0)
  2. Parasuraman

    May 5, 2018 at 1:36 pm

    Very professional approach. Exposes your depth of knowledge! Thanks for sharing!

    Likes(2)Dislikes(0)
    • Suranga Electronics

      May 5, 2018 at 11:20 pm

      Thanks Mr parasuraman

      Likes(0)Dislikes(0)
  3. Muhammad Irfan

    May 5, 2018 at 5:39 pm

    how did you come to know that you found the same transistor from junk board? Because you didn't shared transistor code.

    Likes(2)Dislikes(0)
  4. Henrique Jorge Guimarães Ulbrich

    May 5, 2018 at 7:28 pm

    Very good (and fast), Suranga. Thanks for new knowledge. Just a doubt: The power supply board was not visible.

    Likes(0)Dislikes(0)
  5. Albert van Bemmelen

    May 5, 2018 at 7:41 pm

    Nice work! Question remains what caused it. And that it is not a bad design failure that repeats itself.

    Likes(1)Dislikes(0)
  6. Chigado

    May 5, 2018 at 10:17 pm

    good illustration for beginners.Thanks

    Likes(0)Dislikes(0)
  7. Steve

    May 6, 2018 at 2:21 am

    Sweet nice job

    Likes(1)Dislikes(0)
  8. Andrew F. Ali

    May 6, 2018 at 6:27 pm

    Good job, once again Suranga.

    Likes(0)Dislikes(0)
  9. Yogesh Panchal

    May 6, 2018 at 11:43 pm

    Good Job!Suranga

    Likes(0)Dislikes(0)
  10. Chaminda Jayarathne

    May 8, 2018 at 5:20 pm

    Greet Job Suranga & Thanks to sharing.

    Likes(1)Dislikes(0)
  11. Justice

    May 9, 2018 at 1:14 pm

    Interesting article. You mention 3.3 ;5 and 12 volts from mainboard quite informative,Thanks Suranga.

    Likes(0)Dislikes(0)
  12. Carlo Alberto Birocco

    May 10, 2018 at 4:38 am

    Smart approach to fix the problem. Well done! Thanks for sharing, bro.

    Likes(0)Dislikes(0)
  13. Tito Kanshulu

    May 10, 2018 at 5:06 pm

    Nice work Suranga and thanks for sharing

    Likes(0)Dislikes(0)
  14. Kirwa Boaz

    May 16, 2018 at 9:18 pm

    I have a 32" super slim Lg TV that powers on displays perfectly but after sometime it displays horizontal black lines at the center of the screen and still works well. What might be the problem

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