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LED TV Backlight Prob/Hack?
LED TV Backlight Prob/Hack?
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Old 8th July 2019, 10:27 PM   #1
Formas is offline Formas  Jamaica
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Default LED TV Backlight Prob/Hack?

Good day guys, im working on a Samsung LED backlight tv, the problem i changed one blown LED and it ran for couple weeks, when I open it for backlight problem again its the same LED that i changed blown again. i think its not the right voltage, but that is the only ones i have from another strip (i just cut it and wired it to the strip on top).
My question is "is there any resistor i could or any component to add in series or value that could make that particular led up to par with the rest?" I really dont know the voltages but i only see a 3vdc drop across all when measured, also its 4 strip with 7 LEDs each.
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Old 8th July 2019, 11:19 PM   #2
wiseoldtech is offline wiseoldtech  United States
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Samsung tv's have gotten to be some of the worst ones out there.
Beginning with flat panel sets, the company went downhill fast.
And at the service shop, the Samsung's were the top set coming through the door for repairs.
We couldn't keep up!.
Plus, their customer service was crap, I've had numerous arguments with those snotnoses.

Lawsuits of all kinds from customers were flowing like water.


As a seasoned old tech, guess what brand I favored for my home....... Panasonic!
We hardly ever saw them come into the shop for repairs!
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Old 8th July 2019, 11:32 PM   #3
Fenris is offline Fenris  United States
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As a first order guess, I'd say start with 20-100 ohms per string, quarter or half watt size resistor each. Or a 5-20 ohm if they're all on one string. You may need to test, but this should be a good starting point.
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Old 8th July 2019, 11:33 PM   #4
Formas is offline Formas  Jamaica
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Thanks for the comment @wiseoldtech, wished it was geared toward the problem at hand tho.
can i place like a surface mount resistor on the strip to series the LED i put on? and what value if yes?
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Old 8th July 2019, 11:44 PM   #5
Formas is offline Formas  Jamaica
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Quote:
Originally Posted by Fenris View Post
As a first order guess, I'd say start with 20-100 ohms per string, quarter or half watt size resistor each. Or a 5-20 ohm if they're all on one string. You may need to test, but this should be a good starting point.
can i just put one resistor to the one LED i replace in series for the one strip? it has 7LEDs in series, all the other strips are ok.
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Old 14th July 2019, 02:31 AM   #6
StewartH83 is offline StewartH83  England
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Hey wiseoldtech. Your so right with the Samsung TVs. Surprising the Panasonics don't use the good Panasonic caps though. Only a couple of poly SMDs in mine and had Rubycon and Nichicon in PSU, they good but is this normal from them?

Anyway, test the LEDs well till you get the resistance right. I know u don't want unbalanced back lights as even one low can be annoying
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Old 14th July 2019, 03:13 AM   #7
wiseoldtech is offline wiseoldtech  United States
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Quote:
Originally Posted by StewartH83 View Post
Hey wiseoldtech. Your so right with the Samsung TVs. Surprising the Panasonics don't use the good Panasonic caps though. Only a couple of poly SMDs in mine and had Rubycon and Nichicon in PSU, they good but is this normal from them?

Nothing wrong with Nichicon, I use them all the time - highly reliable.


My Panasonic LED set is now 5 years old and never a problem.


And after servicing about every brand for decades, as I said, the Panasonics rarely came in for service.
But I serviced LOTS of Sonys, Samsungs, LG's, Philips... and those other junk sets like Westinghouse, Emerson, Polaroid, Sansui, etc.
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Old 14th July 2019, 12:38 PM   #8
StewartH83 is offline StewartH83  England
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I can't agree more on the Nichicon caps and reliability of Panasonics. My Sony Bravia that I paid £900 for had issues too. Still got my Panasonic after 10 years with no issue at all. Interesting input of your experience sir
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Old 14th July 2019, 05:06 PM   #9
wiseoldtech is offline wiseoldtech  United States
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Quote:
Originally Posted by StewartH83 View Post
I can't agree more on the Nichicon caps and reliability of Panasonics. My Sony Bravia that I paid £900 for had issues too. Still got my Panasonic after 10 years with no issue at all. Interesting input of your experience sir

Back in the "picture tube era" aka CRT, the Sony Trinitron sets were made quite well, and easy enough to service back then.
However, the later Sony CRT sets were made with less quality - some sets literally "fell apart" due to the plastic used in the cabinets - stress cracks erupted from the heavy picture tubes, with some actually caving in!

But even back then, the Panasonic CRT sets outlasted many other brands.
My best friend bought a Panasonic "Prism" deluxe TV in 1988 which lasted without a problem for 19 years before it finally blew the power supply.
My friend got his money's worth from that nice set, and naturally, with my suggestion, then bought a Pana Viera LCD set, which he still has, and and more recently a Viera LED set.
I've suggested Panasonic to all my friends, and they've all had good luck with them.
Working in the shop for many years allowed me to watch, and follow the quality of sets and how well they held up.
On top of my refrigerator is a 10 inch Panasonic CRT set from 1989, and it's still running perfectly.
NOTE: to any USA customers - Panasonic unfortunately stopped selling their TV's in the USA a few years ago, for the time being, however when they might resume sales is in question.
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Old 14th July 2019, 05:56 PM   #10
takitaj is offline takitaj  United States
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To answer your question without any specifics...

It appears all the LEDs are in parallel. If so then yes you could put a resistor on just the one replacement LED. The only way to know what the value should be is to know the voltage applied to the strip, the forward voltage and the current of the LED you're replacing, etc., BUT, it doesn't seem as that's an option. It's only going to be a guess and the larger you go the dimmer it will be. Since it's burning up the replacement LED I would start out with maybe a 100R or so and see what happens. If it burns again then double it. You can use any style resistor that will fit. You may want to use at least a 1/4 watt just to be safe.

It's just a guess without all the specifics. Good luck!

TJ

Quote:
Originally Posted by Formas View Post
can i just put one resistor to the one LED i replace in series for the one strip? it has 7LEDs in series, all the other strips are ok.
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