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 2= open(323v)
Strip 3=open (323)
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
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:
3) CRT Television repair course and
4) Basic Electronics course.
He is also a blogger at Electronicsrepairmadeasy.com
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