Repeated Failure Of Backlight And Panel Bonding & Replacement In Mr LIGHT LED TV Phantom 32
Those of you, who have not read my article on this TV before, may kindly visit this link and then proceed to read this article. https://jestineyong.com/mr-light-needed-a-backlight-fix/
This TV which was repaired in December, 2021 returned in June, 2022 for the same complaint, i.e., no display. I opened the TV and checked and found that the backlight had failed again, though all precautions were taken before. So I went through the procedure and replaced the backlight. When I checked the voltage, it was showing 41V instead of the ideal voltage of 36 (3V LED x 12). Leaving that to be solved later, I proceeded to re-fix the panel and checked the TV and found that only white light was present and there was no display.
When I checked the side cofs, I found that one of them had some loose contacts. In fact, I had seen a piece of thermal sheet fixed under the middle cof, during my first opening itself, which I had put back like before. But any attempts to maneuver the cof did not bring the display back and I decided that it was time that I took the TV to my friend who runs a shop for panel bonding and repair or replacement of panels. He is an expert and does a good job. His shop was about 20 KMs away from my home. He works on Sundays too to catch up with the work load. This guy I know sometimes works continuously for 24 hours!
He checked and found that the side cof was not the real problem. When we touch it, it gets on due to inductance created by it. There was something wrong inside the panel. But on my insistence, he replaced the cof and also went ahead with the rest of the two too. But the result was same. Then, he did some wiring directly from the scalar board and tried but in vain. After spending several hours and days trying to revive the panel (all due to my insistence), I took my hospital colleague’s consent and agreed for panel changing. The pictures of panel bonding done by my friend are given below, as a gratitude for the yeoman service he did:
The above are screen shots of video I had taken while he was bonding the cofs of Mr Light’s Panel.
Finally, he changed the panel to LG which was available at an affordable price and Mr Light showed his bright picture once again! (LOL) He was so nice that he charged only for the panel and waived off all costs incurred for bonding.
Then I told my friend about the increase of about 5 V for the back light. So, he lifted a couple of resistors from the final driving mosfet to decrease the voltage to 36. Unfortunately, it is hidden under the large capacitor and I could not take snaps of it.
I delivered the TV to my colleague the next day, during my visit to the hospital.
SPECIAL TIPS: There is a couple of protective polythene sheets stuck on both sides of the new panel. While removing the one under the panel is a must to avoid distortion of light falling on the panel, many do not bother to remove the sheet from the front side. These sheets are affixed to prevent any scratches on the panel while in transportation. But if we do not remove it after demonstrating it to the customer, it will cause prevention of dissipation of heat from the panel, resulting in its premature failure. Many including the technicians overlook this and it was my friend who brought it to my focus too! I am sharing this with the readers, duly thanking my friend for pointing this out.
Anyhow, the curtain fell on this Mr Light story, upon which the satisfaction jumped in, which was just waiting for the bag to open its mouth! (LOL)
This article was prepared for you by Parasuraman Subramanian from India. He is 72 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 article on Replacing Two Resistors Solved Three Blinking Problem In SONY LED TV KLV32R402A
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Albert van Bemmelen
August 21, 2022 at 6:26 pm
Your often incredibly difficult tv repair success stories always make me uncomfortable in doing many repairs in this field myself too. Because as you showed they often are impossible to do without special tools or equipment or they still go bad a year or so later. Also in this case replacing the old LCD panel was the only way to fix it.
Parasuraman S
August 21, 2022 at 11:25 pm
Many thanks for your evaluating comments and support!
Henrique J. G. Ulbrich
August 21, 2022 at 8:32 pm
A successful and complicated repair. Greetings. However, I could not understand what is a cof.
Ajay Kumar
August 21, 2022 at 10:46 pm
COF is Chip on Film, an IC used for Panel inter-connection in LED,LCD TVs, Sir.
Parasuraman S
August 22, 2022 at 5:50 pm
Many thanks for your comments and support!
Parasuraman S
August 21, 2022 at 11:27 pm
COF is a short form for Chip on Film. The COFs are bonded to Panel, which is made of glass by a special method. The VGH/VGL and other data lines are fed to panel through this connector. It has an IC on the film which serves as a buffer.
Waleed Rishmawi
August 22, 2022 at 2:11 pm
it is good to have such good tools like that and I bet they have expensive to own but they do the job. thanks for sharing. have a blessed day
Parasuraman S
August 22, 2022 at 5:50 pm
Many thanks for your comments and support!
Imoudu.O
August 23, 2022 at 5:28 am
This is uncommon effect among technicians. I think this boils down for ur passion on tvs.Howerver I thought Mr light will show lg logo, having replace panel with lg panel!!,have a nice day friend.
Parasuraman S
August 23, 2022 at 9:34 pm
LG panel will not show LG logo, as the mother board, its software etc. are unchanged. Only the panel and its T-Con board is connected to the mother board. Unlike Sony or other such complicated sets, there won't be any mismatch when we replace the panel.
Alena Patterson
August 24, 2022 at 8:05 pm
Hello, could you please explain why voltage decreased after removing resistors, should it not be the other way round? Thank you
Parasuraman S
August 25, 2022 at 10:38 am
If a resistor is connected to the ground from the positive voltage rail, the voltage will drop. Such voltage dividing resistors are quite common. If we remove this array of resistors one by one, to suit the voltage requirement, voltage will go up. These resistors are provided in the circuit by the manufacturer only for such purposes. Current also can be limited in such a way, readjusting the resistors provided in the source of the mosfet.
Yogesh Panchal
August 24, 2022 at 11:54 pm
Very tedious Job is panel troubleshooting unlike old CRT TVs most of CRT tubes are identical for replacement.
Parasuraman S
August 25, 2022 at 10:40 am
Yes, you are correct! Many thanks for your comments and sharing your experience!