Don't Miss


LED TV With No Picture But Audio Present Now Repaired

By on October 9, 2020
led tv backlight

 

 

 

 

 

 

 

I got a whatsapp message from one of my neighbor who wanted his television checked by a technician. I visited the place and was shown the television, I applied the power and I could see the power ON led was red and nothing else.

The owner told me that it used to have sound but no picture. With that little introduction I took the television with me to the workshop. I opened the television since I had already done initial tests at the owner’s place.

Once opened the television I decided to go the backlight connector since he talked about audio and dark screen, I suspected backlight problem.

open led backlight

I tested across the two pins of each connector with my backlight tester and indicated open.

led tv backlight tester

As you can see the voltage is 323 volts DC, this is what you expect if the backlight is faulty, if one of the led bead is open.

This is because the beads on a strip are connected in series and therefore if one is open then the whole branch will not drop any voltage. If the led bead short the strip will light but it will be a matter of time before others fail under heavy load since they remaining LEDs will be forced to drop more voltage than normal.

I accessed the backlight by opening the covers slowly and carefully until I finally accessed individual strips as you can below.

led tv backlight failure

I was now able to test individual strips and in this television it has four (4) strips with 12 LEDs each.

Here are the results I got.

Strip 1=28.9Volts

Strip 2= open(323v)

Strip 3=open (323)

Strip 4=28.9Volts

This explain why I was getting open(323V) when testing across the connectors since each connector was supplying two strips and therefore even if one led is open in any of the two strips means the circuit will read open(323v).

With that I decided to go buy the strips and when I reached the market realized that getting these strips with 12 pieces LEDs is not in our market.

The television was over five years old and therefore I did not want to replace individual LEDs since LEDs also suffer aging (have a lifespan) and five years and above they begin to fail. Having no other alternative I decided to use plan B, and the plan was to replace individual LEDs.

To replace individual led you need to use this gadget below called led strip remover and soldering station.

how to test led tv backlight

I replaced all the LEDs with issues and when I was done I again tested individual strips and these were the results.

Strip 1=32.3 Volts

Strip 2= 32.4 Volts

Strip 3=32.4 Volts

Strip 4=32.4 Volts

humphrey kimathi

This looks good since each led has a voltage drop of 2.7V X 12=32.4 volts per strips.




If you want to learn more about replacing individual LEDs you can grab this small eBook which has explained everything you should know about replacing individual backlight LEDs here.

Later I re-assembled the whole thing slowly and carefully and after applying power this is what I saw.

led tv repair with no picture problem

Thank you friends

Stay safe

humphrey kimathi

Humphrey Kimathi is from Nairobi Kenya and he has just launched his new book “Foundations Electricity & Electronics

You can also checkout his other ebooks below:

1) Lcd-Led television repair guide

2) DVD Player repair guide,

3) CRT Television repair course and

4) Basic Electronics course.

He is also a blogger at Electronicsrepairmadeasy.com

Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments. If you have electronic repair articles to share with us, please contact us HERE.

P.S-  If you enjoyed reading the above article, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!

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

https://jestineyong.com/21-inch-crt-toshiba-television-hit-by-lightning-restored-back-to-life-model-21s2m/

 

Likes(50)Dislikes(0)

18 Comments

  1. Parasuraman S

    October 9, 2020 at 9:56 pm

    Excellent and professional work! Well done! Many thanks for sharing!

    Likes(3)Dislikes(0)
    • Humphrey Mndaka

      October 10, 2020 at 2:55 pm

      Thank you Sir Parasuraman,

      Regards Humphrey

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

    October 9, 2020 at 11:04 pm

    Well done pro repair Humphrey! Having the same PTC Heating Plate as you used here, I noticed that it only works when the copper Led Strips are thin. The thicker (mostly with double copper layers) Led strips sadly can't be fixed with this PTC Heater. The heat in those cases simply doesn't reach the layer with the Leds on top.

    Likes(3)Dislikes(0)
    • Humphrey Mndaka

      October 10, 2020 at 2:57 pm

      Quite interesting Albert, in my market we only have cheap china made, actually copy of the copy, think besides selling to Kenya they are also doing dumping hahaha.

      Regards Humphrey

      Likes(1)Dislikes(0)
  3. Aqib Idrees

    October 10, 2020 at 1:51 am

    Wrong. There was picture and sound just no backlight

    Likes(0)Dislikes(1)
    • Humphrey Mndaka

      October 10, 2020 at 3:00 pm

      Not all Tv models shutdown when backlight fail Aqib, kindly do some research on the net and thank me later.

      Regards Humphrey

      Likes(1)Dislikes(0)
  4. Imoudu

    October 10, 2020 at 3:11 am

    Wonderful repair.As a beginer, my first attempt to remove TV screen last two months,I accidentally broke the screen,since then I am always scare to attempt it again. Well I am looking forward to be as good as you are

    Likes(1)Dislikes(0)
    • Humphrey Mndaka

      October 10, 2020 at 3:02 pm

      Hi Imoudu, this eBook will guide you on how to do it like professional.

      https://www.lcd-ledtelevisionrepairguide.com/p/vol1.html

      Regards Humphrey

      Likes(0)Dislikes(0)
  5. babums

    October 11, 2020 at 1:04 am

    very very good work and nicely explained.Thanks for sharing.

    Likes(0)Dislikes(0)
    • Humphrey Mndaka

      October 12, 2020 at 12:35 am

      Thank you for your feedback babums.
      I appreciate.
      Regards Humphrey

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

    October 11, 2020 at 10:00 pm

    Sir,
    Good Repair!
    In last photograph white bright patches are seen on the screen display.
    is that because of Missing LED Reflectors ??

    Likes(0)Dislikes(0)
    • Humphrey Mndaka

      October 13, 2020 at 6:57 pm

      Good question Yogesh, not really because I usually replace back the reflectors back after replacing the bead.
      Regards Humphrey

      Likes(0)Dislikes(0)
  7. Joshua Oloo

    October 12, 2020 at 12:23 pm

    I always enjoy your Articles Hum.please shade more light on the Led lifespan,is the period applicable to all Led or selected Leds?Thanks.

    Likes(1)Dislikes(0)
    • Humphrey Mndaka

      October 13, 2020 at 7:04 pm

      Thank you brother Oloo, for the branded television(Sony, Samsung, LG, Toshiba etc they start failing from around 5years from experience, But for Cheap China made like, Vitron, Hisense, mooka, skyview etc begin failing in less than two years, that is why in Kenya if you don't know how to replace backlight you are missing a lot. harvest is plenty and laborer(techs) are few, you can take that to the back.
      Regards Humphrey

      Likes(1)Dislikes(0)
  8. Alex Obara

    October 14, 2020 at 11:28 am

    Thanks Humphrey. How do you determine the led voltages, I hear leds have different voltages?!

    Likes(0)Dislikes(0)
  9. Humphrey Mndaka

    October 14, 2020 at 11:16 pm

    Hi Alex, by using Led backlight tester.
    Regards Humphrey

    Likes(0)Dislikes(0)
  10. Joven Urbano

    October 18, 2020 at 2:04 am

    It must be tedious replacing each LED bead. I admire your patience. Well done!

    Likes(0)Dislikes(0)
    • Humphrey Mndaka

      October 21, 2020 at 12:40 am

      Hi Joven,
      Only 3 leds were faulty from different strip.

      Regards Humphrey

      Likes(0)Dislikes(0)

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Free Report