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Backlight Replaced And LED Driver Bypassed In LG LED TV MODEL 32LF561D-TF

By on January 4, 2021
Backlight Replaced And LED Driver Bypassed In LG LED TV MODEL 32LF561D-TF

led tv backlight replace

This LG LED TV was brought to me with the complaint that there was no picture, but sound was ok. After observing the Covid Protocol, opened the set and cleaned it as first step.

how to replace led tv backlight

how to replace led tv backlight faulty

Powering the TV, I checked the voltage to the LED and found it to be 217.8V DC, which indicated that there was no load. So, disconnected and removed the Mother, Power Supply Boards and speakers from the rear after removing the connection to the T-Con Board. Disconnected the strip going to the panel, removed the T-Con and the frame protecting the two cofs of the panel.

Removed the screws of the frame holding the panel. Then gently slid out the panel, very carefully handling it not to cause a crack or damage, allowing it to rest on its PVC frame and moved it to a bed nearby.

tcon board checking

Removed the acrylic sheet, polarization film etc. and then disengaged the reflector holding plastic hooks. As I noticed visible burnt marks on a few LEDs on all the strips, removed the three strips which had altogether 18 LEDs with large size domes. Bought three strips of same type from the market and fixed these. We need to peel the old strip carefully with its sticky tape under, clean the base, and then fix the new strip in its place ensuring the connector is in the same place like before. Now let us see the following pictures:

faulty led tv backlight

led tv reflector

lg led tv backlight bad

Then I re-fixed the panel with all its associated parts. As advised by my techie friends, I added a 1.7 Ohm 2 W resistor in series to the 2.3 Ohm resistor at the source of the mosfet to control the current. Since the LEDs bought from the market may not be as good as the original company’s, this is a common practice being followed by my friends. Then reconnected the boards from behind, without fixing these, and applied power. Checked the voltages to the LED and found it to be around 140V, which was definitely wrong, as 6V LED x 18 should take only around 108 Volts. Then I knew that the LED driver circuit was over driving due to some fault somewhere, because of which the original backlight had blown.

I tried even adjusting the brightness, contrast and backlight control to safe levels. But by that time the resistors as well as the mosfet got heated up and smoke was coming from the resistor. So, disconnected and waited for the components to become cool. Then obtained a circuit diagram of the LED driver using IC BD559 and thoroughly checked all the components in the circuit. Everything was fine. So, it could be a problem with the IC itself. Even the mosfet was ok. As the customer was in a hurry, I bought a ready to use LED driver and wired it to the PS Board. (13.2V supply, ground, LED adjust and Driver on) and then wired the LED drive output to the PCB, cutting the tracks coming from the LED drive on the board. Applied power and noticed that the backlight was on, with a voltage of around 179.1V without load and 103.5V on load. This was safe enough to provide a longer life.




This LED driver actually adjusts itself to the required voltage and current sensing the load. So, no hassles at all! So, fixed the PS board back and also fixed the new board on one of its screws. Kept an old mobile cover underneath and applied Fevibond. Now the connected pictures:

led tv circuit board repair

led tv board repair

how to fix led tv driver board

fixing led tv with backlight problem

circuit track cut for isolation

troubleshooting led tv lg with backlight fault

Allowed the set to run for a few hours and then fixed the back cover. Called the customer and informed him to collect it. Here are a couple of pictures to provide a finale, without forgetting to add the satisfaction to its collection bag!

LG Led Tv backlight problem fixed

This article was prepared for you by Parasuraman Subramanian from India. He is 71 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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You may check on his previous repair article below:

https://jestineyong.com/partial-failure-of-sony-am-fm-ic-cxa1238s-found-in-module/

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10 Comments

  1. Imoudu Onwumah

    January 4, 2021 at 7:47 pm

    Thanks for the info,however which of the tracks did you cut off to connect led driver module?

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

      January 4, 2021 at 10:48 pm

      Good job my friend. The Universal Drive CA-288 is what I use also. There are bridge points to allow for more current if the picture was still a bit dark but with a 32inch TV leaving them open is fine.

      Likes(2)Dislikes(0)
      • Parasuraman S

        January 6, 2021 at 9:24 pm

        Many thanks for your comments and tips!

        Likes(0)Dislikes(0)
    • Parasuraman S

      January 6, 2021 at 1:18 pm

      The two tracks to which the LED backlight connector is getting joined. (+/-)

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

    January 4, 2021 at 8:00 pm

    Good job of course with much work done! Of which you deserve all credits! Sadly, seeing the small photos, it is still unclear what LED driver board you exactly used to replace the old board? And it is hard to obtain the right replacement LED Driver board without knowing what the specs were that made you decide what board was the right one for your repair?

    Likes(4)Dislikes(0)
    • Parasuraman S

      January 6, 2021 at 1:21 pm

      In this case, my techie friends do advise me from their experiences. I just carried out what they told me, as there was no time to make a detailed study. The customer was in a hurry as mentioned in the article and I just gave it off! Unfortunately I do not have a close up photo of the ICs used in the LED driver board!

      Likes(1)Dislikes(0)
  3. Yogesh Panchal

    January 4, 2021 at 11:35 pm

    Sir,
    Request you....In your articles please arrange the photographs as per the troubleshooting order and Mark the faulty components with arrow or circle so that it is easy to understand the article.because some peoples keep the article for their future reference.
    anyway professional fault finding keep up sharing.

    Likes(2)Dislikes(0)
    • Parasuraman S

      January 6, 2021 at 1:24 pm

      Many thanks! I do mark such cases (Please see old articles). In this case, all the three strips were replaced and there was nothing to mark! I have already marked the new strips, with the defectives on the previous image, which can easily be understood. Anyhow, shall take care of your advice!

      Likes(0)Dislikes(0)
  4. Sakhe

    February 17, 2021 at 1:39 pm

    Hi sir... I have a problem with my LG 55 inch tv. I replaced all the strips with other from another TV bt now my backlights are 2 dim now how can I make them bright.. Thank u in advance

    Likes(0)Dislikes(0)
  5. Henry

    April 7, 2021 at 10:08 pm

    Good job sir, nice work you are doing

    Likes(0)Dislikes(0)

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