How To Repair LED TV Mainboard
This LG LED 24 Inch TV came in for repair with the complaint of no power. For this model, it did not use the switch mode power supply board and in fact it uses an external power adapter that was rated 19 volt -1.6 Amp. You can check out the two photos below:
For a no power symptom TV, the first thing to do is to check the output dc voltage from the external power adapter. If there is no output voltage then the power adapter is at fault.
In this case, the power adapter was checked to be good and it measured 19.11 Vdc-see the photo below:
Since the power adapter was working fine this means I have to open the TV cover and check on the mainboard. The photo below is the LED TV mainboard:
Usually for this kind of problem I will start to check from the Power Jack area first. I checked on the protection SMD resistor (R100=10 Ohm) and it was open circuited. This component acted like a fuse and will open circuit when there is a over current drawn.
Once this protection resistor was open circuited, we have to find out what causes the problem. After checking on the few components nearby I confirmed that only one Power FET was shorted.
I soldered out the two components and put the replacement parts. For the power FET I got it from another TV junkboard.
After fixing the two components and powered On, the TV came back to life. I was very happy because there was no other bad components. Another job done and earn some profits.
Conclusion- Don’t immediately repair the TV mainboard or any other mainboards unless you have carefully studied how the mainboard works. Otherwise you will be shooting in the dark as where to start to check and this will cause your time lost. If you want to be excel in LCD/LED TV repair you can check out on Kent’s and Damon’s ebooks.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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Note: You may check out his previous post in the below links:
https://jestineyong.com/what-an-ingenius-way-to-solve-a-power-supply-with-burnt-components/
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Parasuraman
July 30, 2018 at 10:35 am
It's a pleasure to see how you approach a problem and solve it professionally! Excellent!
Suranga Electronics
July 30, 2018 at 4:51 pm
Thanks !
Mr, Parsuraman.
Ganthan
July 30, 2018 at 11:51 am
Well done Suranga. Keep it up..
Albert van Bemmelen
July 30, 2018 at 2:39 pm
Pro repair with great detailed article. I bought Damon's and Kent's newest tv repair e-books. Damon's book convinced me to also buy a RT809H universal programmer to fix the Nand chip problems that he says exists in many devices! Since even laptop mainboards, desktop computers and gameconsoles (like the XBOX360) can't work without them it is very good advice. Because universal programmers like the Genius 540 or the much appreciated TL866C simply can't read or write to those special memory chips. The RT809H can and much more!
Humphrey Mndaka
July 30, 2018 at 5:30 pm
Thumb up Suranga..Keep going!
Regards Humphrey
Robert Calk Jr.
July 30, 2018 at 6:49 pm
Good job, Suranga.
Mihai
July 31, 2018 at 12:52 am
Hello Suranga,
Thanks for sharing !
R.S. Jayasekara
July 31, 2018 at 1:21 am
Mr. Suranga,
What a nice trouble shooting, great-work and all the best.
Yogesh Panchal
August 1, 2018 at 12:19 am
Good job! suranga
Andrew F. Ali
August 1, 2018 at 3:17 am
Sometimes measuring the voltage on power supply blocks aren't enough. The voltage may be good but it doesn't have the amps So for me the best way to test these PSUs are the put a load on it. I use incandescent car bulbs in series for this particular PSU. BTW these block PSUs are SMPS. Great work however in finding the issue here and getting this TV up and running again.
Robert Calk Jr.
August 2, 2018 at 7:48 am
That's true. I use my little YZX Studio USB power monitor and electronic load. The YZX load is good to 3A which is good enough for most power supply blocks.
Humberto
August 1, 2018 at 11:13 pm
Good job Suranga. Congratulations.
Tito
August 1, 2018 at 11:31 pm
Great job Suranga and a good suggestion from Ali too. It really works
D. Wilson
August 4, 2018 at 9:59 am
meticulous. Thanks for sharing.
Tyrone Arendse
August 10, 2018 at 1:05 am
Hi I just want to say that I am learning a lot from you
irwan
November 4, 2018 at 10:02 pm
nicely done..tq for sharing
Mrityunjay Bhuyan
September 5, 2020 at 11:48 am
I am having the same tv, Main IC of the board is overheating, and only two times blink the red led, what might be the problem? please help.
DOĞAN
December 19, 2020 at 2:00 am
I enjoy reading your repairs. Loves from Turkey...
niro
November 9, 2021 at 9:49 pm
suranga, im from srilanka, i got 49mu7350 tv. suddenly no power indicating to power on , while backlight light up when detach power board and mainboard connection.
Anthony
April 14, 2022 at 9:29 pm
Well done just came across your web page but was impressed by your diagnostic skills. Keep it up and grow your business.