SMD Mosfet Found Dislodged In LED TV Model 32LF561D
This TV which visited me in December, 2020 about which I had already published an article, link of which is provided below, returned in July, 2023. I am not repeating the images to provide brevity to this article, to cut short desktop time of our beloved, Jestine Yong, who is professionally a very busy person.
https://jestineyong.com/backlight-replaced-and-led-driver-bypassed-in-lg-led-tv-model-32lf561d-tf/
This time, the complaint was that the TV was not having any display but had sound. Naturally, I thought it might be due to failure of back light once again. I opened the TV and subjected it to thorough cleaning.
Then when I looked at the LED driver board, I was surprised to see that the driver Mosfet had got dislodged from its original position and shifted to left side! Luckily it did not cause any shorts, which might have resulted in burn or even fire!
I removed the Mosfet and checked and found it to be working ok. So, I fit it back and applied power through a series bulb. The bulb lit up indicating a dead short. The Mosfet (PGF640N) became totally short! So, it might have developed a small leak, increasing the temperature to such an extent that the solder melted and displaced it.
Anyhow, I used an equivalent through-hole type Mosfet (IRF640N) and fit it in place for testing the output. Applied power and was glad to see the output was ok. I replaced all the electrolytic caps on the board as a preventive maintenance. First I thought of using the following Universal Backlight Driver, but the output was only 84 V on load and the LEDs did not light up. I had already checked the LEDs using my LED Checker and found these to be ok, which I forgot to mention in the beginning.
Then fit the Led driver board and applied power to see a good and bright light. The voltage reading was 110.94 and current drawn was 186mA, which were quite normal and safe. Provided heat zinc and bent the Mosfet to a slanting position so as not to touch the back cover. I provided clip on connectors to the LED driver this time, for easy removal and trouble shooting.
I allowed the TV to run for hours together for two consecutive days, before offering for pick up by customer. Mission accomplished satisfactorily qualifying itself to get entry into the collection 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 What Will Be The Symptom When VGH Is Missing In LED TV? – SAMSUNG UA24H4003AR
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Steve
November 26, 2023 at 8:55 am
Parasuraman, love your repair stories. Glad to see devices saved from being discarded.
I hope I can still repair things when I'm 72, also hope I look as good (too late) 🙂
Parasuraman S
November 26, 2023 at 11:03 am
Many thanks for your wonderful comments! I wish and pray that you get enough energy and inspiration to continue your repairs to keep up your passion. I am 74 now; I forgot to tell Jestine Yong to update it. Shall do so soon! Thanks for bringing it to my attention!
Waleed Rishmawi
November 26, 2023 at 1:17 pm
Good repair work my friend. I did not know that you are 74 years old. Keep up the good work and have a blessed day.
Parasuraman S
November 26, 2023 at 2:30 pm
Many thanks, dear friend!
Albert van Bemmelen
November 26, 2023 at 5:54 pm
Seeing the photos with the large leaking 680uF/35V e-cap on the led driver board with the brownish looking gunk on top of the capacitor never can be a good sign. I guess that it had something to do with the dislodged and now replaced mosfet.
Parasuraman S
November 26, 2023 at 9:58 pm
Could be inter connected. Thanks for your comments!
tony
November 27, 2023 at 3:07 pm
Age is just a number
There is no substitute for experience.
Young people wish there was a pill that
could just give them 30 years experience
instantly.
Unfortunately for them 30 years experience
takes 30 years to acquire but is not equal to
doing the same one years experince 30 times over.
We older people know a thing or three now.
Parasuraman S
November 27, 2023 at 8:04 pm
Many thanks for your comments and encouragement.
Yogesh Panchal
November 28, 2023 at 3:39 pm
Good Job! Sir
Parasuraman S
November 28, 2023 at 9:01 pm
Thanks dear!