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
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ANIL KUMAR V K
August 27, 2022 at 8:47 am
Excellent work sir, thanks for sharing
Parasuraman S
August 28, 2022 at 9:04 pm
Many thanks for your support!
Tayo
August 27, 2022 at 9:03 am
Excellent tip regarding heat transfer and management Sir. Running the LEDs at 100% brightness seems to be the norm and i suspect is done at the factory. I have even added some fans to TVs (like they used to have on our ould plasma TVs) to help with cooling. Only time will tell if they are of any help.
Parasuraman S
August 28, 2022 at 9:06 pm
Adding a cooling fan is a good method. Many thanks for your comments and support!
Waleed Rishmawi
August 27, 2022 at 12:39 pm
Great repair my friend. That is why a bought a used TV set for my son to play his PS4 and not use the main tv in the house. Have a blessed day.
Parasuraman S
August 28, 2022 at 9:06 pm
A wise decision, satisfying both! Many thanks for your comments and support!
Albert van Bemmelen
August 27, 2022 at 2:29 pm
I take it that the repair after 1,5 years was out of any 'warranty' on replacing the backlight led strips. And I understand why you took no chances by this time also replacing all questionable e-caps.
Parasuraman S
August 28, 2022 at 9:10 pm
There is no warranty on the backlights. As a gesture of goodwill, failure within a short while will either be charged only for the cost of components replaced or appropriate concessions passed on. As you know, customers are a good window for our fame and name. It takes only one wrong move to spoil it! Many thanks for your comments and support!
Imoudu.O
August 27, 2022 at 3:29 pm
Great repair friend, and when you repair tv last year, did you change all led strips as at then?
Parasuraman S
August 28, 2022 at 9:11 pm
Yes, dear. I always change all the strips, as described in the article. We should not make a partial replacement. Many thanks for your comments and support!
RAHEEM WAKHEEL OLAWUYI
August 27, 2022 at 10:25 pm
GREAT JOB, please it's all strips were detect or only one ?, because am thinking of cost by changing all strips
Parasuraman S
August 29, 2022 at 3:44 pm
Whenever we do a replacement of backlight, we need to change the entire strips, as otherwise there would be a mismatch of current drawn and it would fail soon. This is a universally accepted good practice. In this case, there were a few working strips. But I returned all those to customer along with the defective pieces, as per my usual practice.
Emma
September 1, 2022 at 6:07 pm
Thanks for this, is it not good to use old strip with new one?
Parasuraman S
September 2, 2022 at 8:28 pm
Kindly read my comments above. Old strips should not be mixed with new ones. Many thanks for your comments!
GIFT ELIJAH
September 4, 2022 at 11:39 am
Thanks so much for the detailed explanation on the repairs and your special policy of giving the customer the changed parts.I have now learned to always change all the old strip whenever any of them is faulty.
Please sir, at what point can a technician conclude that the screen of a TV is totally bad and needs replacing ( what kind of fault can make a technician recommend for replacement of tv screen?)
Parasuraman S
September 8, 2022 at 6:06 pm
Dull light even at full brightness or backlight control, yellowish or bluish light (in some TVs like LG the LED turns blue!) Error indication of blinking codes, normally six in Sony when you switch on TV. If the inverter is generating the voltages when checked and drops or either remains full and gets dropped, the LED backlights are bad. More current drawing than allowed in the circuit protection is another defect. In this case, there won't be any backlight issue. But TV will go to blinking mode or standby.
Yogesh Panchal
September 8, 2022 at 4:10 pm
Sir, Another Good Fix!
A Perfect professional repair. I seen many technicians just replacing Standard LED by just matching the voltages by ignoring Wattage & Current Specifications of LED which may lead customer to suffer.
Parasuraman S
September 9, 2022 at 12:07 pm
Yes, commercial technicians cherish return of a set after a reasonable gap as it is their nourishment! (LOL) Many thanks for your comments!