Unexpected Shorted Parts In LG LED TV

By on August 3, 2018
checking the 5 volt voltage at mainboard in led tv

 

 

 

 

 

 

 

 

 

 

lg led tv no power

Customer sent to me this 22 inch LG LED TV with the complaint of no power. The model of this TV is 22LD310. I have connected the AC power to the TV and indeed, it was no power. The reason I test the TV again is because sometimes the problem could be different of what the customer actually complaint at.




For example, when you turn on the TV there is power LED, after few seconds later the power LED went off. This symptom is totally different from a no power fault.

lg led tv no power repair

metal cover

Once the metal cover was removed I can access to the connector to check on the DC output voltage. Since the main fuse did not blow, so to confirm it is actually power supply fault or mainboard fault is to measure the DC output voltage. The result was zero volt and this indicated it was the power supply fault.

checking the 5 volt voltage at mainboard

The next step is to check on the components in the power primary side. I found one zener diode component was shorted and others corresponding components seems to be good. I thought I have repaired the set by replacing the zener diode but the problem was still the same. The below photo is the result of a shorted zener diode:

no power in lg led tv 22 inch

I did not give up and continued to check on other components such as secondary side output diodes and Optoisolator IC.




You wouldn’t believe if I told you the Optoisolator IC was short circuited in the phototransistor side.

pc817 opto ic bad

A new replacement part of PC817B (4 leads) cured the fault. Below are the photos of a lighted LED and a working TV set.

how to fix no power fault in LG led tv

repairing lg led tv

Conclusion- If you want to learn how to test components to perform the electronics repair work you can get Jestine Basic Electronics Repair ebook Here. If you want to be a professional in switch mode power supplies repair then you need to check out his another ebook HERE. Ok see you in the next article.

suranga

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




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Note: You may check out his previous post in the below links:

http://jestineyong.com/how-to-repair-led-tv-mainboard/

 

 

 

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9 Comments

  1. Parasuraman

    August 3, 2018 at 5:56 pm

    A good troubleshooting with rich experience to approach coolly!

    Likes(4)Dislikes(0)
    • Suranga Electronics

      August 4, 2018 at 1:14 am

      Thanks Mr,parasuraman

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

    August 3, 2018 at 8:48 pm

    Nice work again, Suranga.

    Likes(3)Dislikes(0)
    • Suranga Electronics

      August 4, 2018 at 1:15 am

      Thanks Mr,

      Likes(2)Dislikes(0)
  3. Robert Calk Jr.

    August 4, 2018 at 2:52 am

    Good work, Suranga.

    Likes(2)Dislikes(0)
  4. D. Wilson

    August 4, 2018 at 9:49 am

    Great job. However, you should have been a little more thorough when you analyze the power supply the first time. If you were, you would have found the defective optocoupler.

    Likes(1)Dislikes(0)
  5. Albert van Bemmelen

    August 4, 2018 at 2:36 pm

    Pro job! I'm glad that I've fast digital testers for easily checking those 817 and other optocouplers. Even testing opamps and some amplifier chips are no problem for my fast digital testers. Including of course the TTL and CMOS IC range. And saving time is always good!

    Likes(2)Dislikes(0)
    • Hakan

      August 5, 2018 at 11:54 pm

      Hi, may you give their names of those testers?

      Likes(1)Dislikes(0)
  6. Humberto

    August 10, 2018 at 10:26 pm

    Wow! Suranga. What a repair! Congrats.

    Likes(1)Dislikes(0)

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