Backlight Failure After One And Half Years In LG 42LF550T
Those of you, who have not seen my previous article on the same TV, may please see the same from the following link:
This time, the customer reported that the backlight was blinking and sometimes it comes on or goes dead. Rather, it was intermittent. I opened the set and cleaned the inside. When the backlight was tested with my LED checker, it showed zero consumption indicating defects. I then dismantled the whole TV, without which we cannot access the backlight.
When I checked the strips individually, only one strip was defective. But these are connected in series and any defect on the path will affect the whole light. I peeled off the strips and applied gum remover spray and used a thistle to scrape off the old gum thoroughly.
Then kept the bare chassis in sunlight, in front of my house for more than an hour to allow evaporation. This cleaning is absolutely essential, as heat dissipation from the LED strip should be firm. Dried gum will prevent this and LEDs might fail soon. Here are the pictures. Look how clean the strip base is!:
Then fixed the new strips observing A on left and B on the right like how it was, joining them in the middle and aligning it neatly on the base. B has the connector on its right side. Look how neatly the new strips were laid:
After reassembling, I checked and ensure that the backlight was working very well and the voltage that goes is near 190V like before. It was reading only around 187 this time. 32 LEDs x 6V should consume around 192V. So, the voltage range was within safe limits.
I also replaced the 10/350V caps of the inverter along with the 470/25V caps and other two caps in the power supply as these were found to be slightly out. After re-checking and ensuring all connections are back to its original condition, I applied power and found the result damn good!
I observed that the backlight was set to 100%; so was the brightness and contrast, which are the reasons for failure of backlights!
Even though we educate the customers, children who play games or watch cartoons in the TV, tend to meddle with the settings to suit their taste. Here are the pictures of the old backlights and caps:
I ran the TV for almost 6 hours totally in two sessions and found it to be working very well. Satisfaction was more than ready to jump into its bag.
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 Repeated Failure Of Backlight And Panel Bonding & Replacement In Mr LIGHT LED TV Phantom 32