LED TV With No Picture But Audio Present Now Repaired
I got a whatsapp message from one of my neighbor who wanted his television checked by a technician. I visited the place and was shown the television, I applied the power and I could see the power ON led was red and nothing else.
The owner told me that it used to have sound but no picture. With that little introduction I took the television with me to the workshop. I opened the television since I had already done initial tests at the owner’s place.
Once opened the television I decided to go the backlight connector since he talked about audio and dark screen, I suspected backlight problem.
I tested across the two pins of each connector with my backlight tester and indicated open.
As you can see the voltage is 323 volts DC, this is what you expect if the backlight is faulty, if one of the led bead is open.
This is because the beads on a strip are connected in series and therefore if one is open then the whole branch will not drop any voltage. If the led bead short the strip will light but it will be a matter of time before others fail under heavy load since they remaining LEDs will be forced to drop more voltage than normal.
I accessed the backlight by opening the covers slowly and carefully until I finally accessed individual strips as you can below.
I was now able to test individual strips and in this television it has four (4) strips with 12 LEDs each.
Here are the results I got.
Strip 1=28.9Volts
Strip 2= open(323v)
Strip 3=open (323)
Strip 4=28.9Volts
This explain why I was getting open(323V) when testing across the connectors since each connector was supplying two strips and therefore even if one led is open in any of the two strips means the circuit will read open(323v).
With that I decided to go buy the strips and when I reached the market realized that getting these strips with 12 pieces LEDs is not in our market.
The television was over five years old and therefore I did not want to replace individual LEDs since LEDs also suffer aging (have a lifespan) and five years and above they begin to fail. Having no other alternative I decided to use plan B, and the plan was to replace individual LEDs.
To replace individual led you need to use this gadget below called led strip remover and soldering station.
I replaced all the LEDs with issues and when I was done I again tested individual strips and these were the results.
Strip 1=32.3 Volts
Strip 2= 32.4 Volts
Strip 3=32.4 Volts
Strip 4=32.4 Volts
This looks good since each led has a voltage drop of 2.7V X 12=32.4 volts per strips.
If you want to learn more about replacing individual LEDs you can grab this small eBook which has explained everything you should know about replacing individual backlight LEDs here.
Later I re-assembled the whole thing slowly and carefully and after applying power this is what I saw.
Thank you friends
Stay safe
Humphrey Kimathi is from Nairobi Kenya and he has just launched his new book “Foundations Electricity & Electronics”
You can also checkout his other ebooks below:
1) Lcd-Led television repair guide
3) CRT Television repair course and
4) Basic Electronics course.
He is also a blogger at Electronicsrepairmadeasy.com
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19 Comments
Leave a Reply
Parasuraman S
October 9, 2020 at 9:56 pm
Excellent and professional work! Well done! Many thanks for sharing!
Humphrey Mndaka
October 10, 2020 at 2:55 pm
Thank you Sir Parasuraman,
Regards Humphrey
Albert van Bemmelen
October 9, 2020 at 11:04 pm
Well done pro repair Humphrey! Having the same PTC Heating Plate as you used here, I noticed that it only works when the copper Led Strips are thin. The thicker (mostly with double copper layers) Led strips sadly can't be fixed with this PTC Heater. The heat in those cases simply doesn't reach the layer with the Leds on top.
Humphrey Mndaka
October 10, 2020 at 2:57 pm
Quite interesting Albert, in my market we only have cheap china made, actually copy of the copy, think besides selling to Kenya they are also doing dumping hahaha.
Regards Humphrey
Aqib Idrees
October 10, 2020 at 1:51 am
Wrong. There was picture and sound just no backlight
Humphrey Mndaka
October 10, 2020 at 3:00 pm
Not all Tv models shutdown when backlight fail Aqib, kindly do some research on the net and thank me later.
Regards Humphrey
Imoudu
October 10, 2020 at 3:11 am
Wonderful repair.As a beginer, my first attempt to remove TV screen last two months,I accidentally broke the screen,since then I am always scare to attempt it again. Well I am looking forward to be as good as you are
Humphrey Mndaka
October 10, 2020 at 3:02 pm
Hi Imoudu, this eBook will guide you on how to do it like professional.
https://www.lcd-ledtelevisionrepairguide.com/p/vol1.html
Regards Humphrey
babums
October 11, 2020 at 1:04 am
very very good work and nicely explained.Thanks for sharing.
Humphrey Mndaka
October 12, 2020 at 12:35 am
Thank you for your feedback babums.
I appreciate.
Regards Humphrey
Yogesh Panchal
October 11, 2020 at 10:00 pm
Sir,
Good Repair!
In last photograph white bright patches are seen on the screen display.
is that because of Missing LED Reflectors ??
Humphrey Mndaka
October 13, 2020 at 6:57 pm
Good question Yogesh, not really because I usually replace back the reflectors back after replacing the bead.
Regards Humphrey
Joshua Oloo
October 12, 2020 at 12:23 pm
I always enjoy your Articles Hum.please shade more light on the Led lifespan,is the period applicable to all Led or selected Leds?Thanks.
Humphrey Mndaka
October 13, 2020 at 7:04 pm
Thank you brother Oloo, for the branded television(Sony, Samsung, LG, Toshiba etc they start failing from around 5years from experience, But for Cheap China made like, Vitron, Hisense, mooka, skyview etc begin failing in less than two years, that is why in Kenya if you don't know how to replace backlight you are missing a lot. harvest is plenty and laborer(techs) are few, you can take that to the back.
Regards Humphrey
Alex Obara
October 14, 2020 at 11:28 am
Thanks Humphrey. How do you determine the led voltages, I hear leds have different voltages?!
Humphrey Mndaka
October 14, 2020 at 11:16 pm
Hi Alex, by using Led backlight tester.
Regards Humphrey
Joven Urbano
October 18, 2020 at 2:04 am
It must be tedious replacing each LED bead. I admire your patience. Well done!
Humphrey Mndaka
October 21, 2020 at 12:40 am
Hi Joven,
Only 3 leds were faulty from different strip.
Regards Humphrey
Ali
December 6, 2020 at 3:37 pm
Great work ..please can i ask what the most important devic like tester ....i need to make my work more good ..thank you