Good day folks. I thought I'd share with you a little something that's happened to me which I haven't seen so far and to also ask for a little advice in the process. I received an LG TV (can't remember the model right now since I'm writing from home and didn't snap a picture of it, that's why I said "coming soon" in the title bar) with dead backlight. Simple enough I thought. I took off the panel to access the LEDs and started testing them one by one....none of them would come on ! NOT ONE ! A couple of them were visibly burnt, showing black stuff under the lenses, but the others seemed clear enough, yet they refused to even shine a little. Thinking perhaps I'm putting my supply's probes in the wrong places (though it's certainly not the first TV of this kind I'm messing with), I took my meter and measured in continuity mode: I'm reading shorts across the end contacts of all 3 LED strips. No wonder the test supply was not doing anything - it was just shorting out, since it's just a small 5v AC adapter, without any meter or indicator, so I couldn't tell what it was doing. ALL LEDs dying in a TV like that ? That's a first if I ever saw one...I can't begin to imagine how it could've happened for one thing and second I'm a bit reluctant to replace the strips, fearing there's something wrong with the PSU and it will fry those too...what do you guys think ? Strange am I right ? :\ Cheers.
LG TV (model coming soon) with ALL LEDs dead ?!
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Re: LG TV (model coming soon) with ALL LEDs dead ?!
You have shorted LEDs in all strings or maybe PCB damage on the strips, so the strips most likely need replacement. Doubtful it would be caused by the PSU of the TV, they're just overdriven from the factory, and people leaving the TV at the same settings it was put at in the store doesn't help, either. But after you get it repaired, a small modification to the LED driver to limit the maximum current would be a good idea, ensuring this doesn't happen again.Last edited by Th3_uN1Qu3; 03-29-2018, 09:47 AM.Originally posted by PeteS in CARemember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company. -
Re: LG TV (model coming soon) with ALL LEDs dead ?!
A short on the very ends of each strip would imply that all LEDs in that strip failed shorted...sometimes they fail open, which wouldn't read a short, at least not on the ends.
I've seen people talking about modifying the output of the LED driver but haven't really looked into it myself and haven't done it before. My knowledge of electronics would tell me it's done by changing the value of some resistor divider which sets the output current the supply is trying to reach....just a guess.Wattevah...Comment
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Re: LG TV (model coming soon) with ALL LEDs dead ?!
Is there protection diode on each LED strip?Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: LG TV (model coming soon) with ALL LEDs dead ?!
does this set use the 3v or 6v version leds does seem odd all failedComment
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Re: LG TV (model coming soon) with ALL LEDs dead ?!
Hi,
Take a look at the underside of the power supply board. See if they use a BD9483F as the led driver. Also check for loose solder joints on some of the electrolytic capacitors.
I've fixed two LG 50LN5400-UA sets with some bad leds.
If you search for the data sheet on the above driver ic you will find that they have a formula to calculate the current flowing through the led strips. The value of the sense resistors determine the current allowed. I increased the value of the resistors to lower the strip current.
The board that I modified was EAX64905501 (2.1).
I don't want to suggest that this is a fix as I don't have data to support it.
I did not notice any reduction in the brightness that affects viewing after I did the modification.
MikeComment
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Re: LG TV (model coming soon) with ALL LEDs dead ?!
I have a 49 inch LG right now that has 25 out of the 50 LEDS blown! I believe these are the 6v ones. They have the wide angle lenses on them that like to fall off. Unbelievable. Rubbish.Did I leave the soldering iron on?Comment
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Re: LG TV (model coming soon) with ALL LEDs dead ?!
Replaced the strips in this TV and it works perfectly. The problem turned out to be one of the LEDs on the bottom strip puncturing a hole through the strip and arcing on the metal chassis below.....or so I think....anyway. Case closed.Wattevah...Comment
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