LG47LN5200 UB LCD TV - Backlight LED's


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LG47LN5200 UB LCD TV - Backlight LED's

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MJS60
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Aug 2, 2016, 10:16 PM

Post #1 of 12 (4311 views)
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LG47LN5200 UB LCD TV - Backlight LED's	Can't Post

I guess shorted or open backlight LEDS on LG models are a very big problem? I would have thought that they would have been more reliable than the older florescent bulbs. I guess not! After finding out that 4 LEDS had failed I bought one LED strip on eBay and it did fix one string on the TV that I assume was shorted since the strip didn't work at all. I was hoping to use the good LED's on the used strip to fix 3 other strips on which one LED is dead(open). These other 3 strips all worked except for a single LED out. So I assume that they were all open while the culprit was shorted? The strip I bought fixed the one LED that was shorted and pulling down the power supply so I had 4 good LED's left to work with on that strip. I must say that the heat gun that was recommended on an Youtube video is no match for a good Metcal soldering station with a tweezers attached and is much more difficult than it looks to desolder the LED off the strip. My question is, after desoldering one LED off another strip and without adding a new LED, why can't I get the strip to work now? Pad is not damaged nor is there a solder bridge. I thought the LEDS were all in parallel on this strip? If so they should have lit with only that one LED gone. Any suggestions? Youtube video I used is at: <a href="https://www.youtube.com/watch?v=Bf5T2wwtydY" target="_blank">https://www.youtube.com/watch?v=Bf5T2wwtydY</a> 

(This post was edited by MJS60 on Aug 3, 2016, 6:07 PM)

jts1957
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Aug 3, 2016, 2:41 AM

Post #2 of 12 (4303 views)
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Re: [MJS60] LG47LN5200 UB LCD TV [In reply to]	Can't Post

The LEDS are all in SERIES on this strip.

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Location: Far, Far Away

(This post was edited by jts1957 on Aug 3, 2016, 2:41 AM)

MJS60
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Aug 3, 2016, 4:04 AM

Post #3 of 12 (4299 views)
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Interesting, so why if one opens the rest still light? One LED was shorted on the worst strip and it did take out the strip but do some also partially short and the rest of the LEDS still work? I have 3 LEDS that are dead on 3 other strips but I still have good brightness on all of them.

jts1957
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Aug 3, 2016, 8:18 AM

Post #4 of 12 (4288 views)
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Re: [MJS60] LG47LN5200 UB LCD TV [In reply to]	Can't Post

What is panel number?
IF LC470DUE-SFR1 - Datasheet (page 7) shows series strings.

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MJS60
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Aug 3, 2016, 5:27 PM

Post #5 of 12 (4280 views)
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Re: [jts1957] LG47LN5200 UB LCD TV [In reply to]	Can't Post

Panel #? - I have no schematic but now it is beginning to make sense as to why the LEDS are behaving the way they do on the strips. 24v applied to the complete strip turns on the strip and 12v applied to the half strip turns it on when troubling shooting. Still I don't understand why the non-working LEDS on some of the strips don't cause the entire strip to not light if they are wired in series. If any of the LEDS are open shouldn't that take out the whole strip? And if they are catastrophically shorted same thing but it will pull down the power supply and in my case one LED was shorted that badly, thus causing the TV to only flash for a split second and not come on. I understand that. Also can the single LEDS be ordered? Right now I've only managed to find the strips and they are $19.95 each. Too high to pay for only the 3 LEDS left that I need to repair this TV. Good LED's are also incredibly hard to get off an old strip without damaging it if using a heat gun. This strip acts as a very good heat sink since it is mostly copper! Since my retirement as an engineer, I no longer have access to a good Metcal Station with desoldering Tweezers so a single new LED source would be the cheapest solution. The strip part numbers are: R1 Type 6916L-1176A LED STRIP (4 LED's on the strip) R2 Type 6916L-1174A LED STRIP (5 LED's on the strip) 

(This post was edited by MJS60 on Sep 27, 2016, 7:33 PM)

MJS60
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Aug 3, 2016, 6:11 PM

Post #6 of 12 (4274 views)
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I've just found out more data on this LED and here is the information to order them, but so far most places are in China and the last time I ordered there it took about a month to get the part! Are there any places in the US that I could get them at cheap too? I'd like to get at least 12 pcs.

Specification :
3528 2835 SMD LED 1W LG Cool White
Model Number: LATWT470RELZK
Brand Name: LG
Forward Current: 400mA
Size: 3.5*2.8*0.6mm
lumens: 100LM
Forward Voltage: 3.05-3.65V

(This post was edited by MJS60 on Aug 3, 2016, 6:13 PM)

jts1957
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Aug 3, 2016, 6:24 PM

Post #7 of 12 (4269 views)
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http://imgur.com/yCeOm6e

Mouser, Digikey or if on the other side of the big pond https://www.rapidonline.com/Surface-Mount-LEDs (I like their page organization).
Bear in mind that installed NEW LEDs will most likely NOT match your originals brightness, color temp or longevity. (Unless you have originals specs) Wink

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(This post was edited by jts1957 on Aug 3, 2016, 6:27 PM)

MJS60
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Aug 4, 2016, 2:21 AM

Post #8 of 12 (4257 views)
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Thanks JTS1957 for pointing me in the right direction. I was able to get one of the old LED's off the strip but I killed the other 3 so only 2 LED's are out now on separate strips and brightness seems fine except for those two. I'm still trying to decide if I should just put it back together or order the other two. I'm thinking the person that gave this TV to me had the brightness turned to Max so maybe I should order at least 20 or more of them since the lead time is so long overseas and if I don't repair it right I might be back into it again. Working inside LCD screens is not my favorite kind of repair! I'm also aware that the Chinese rarely bin or match their LED's that is why I'm trying to get exact replacements. I worked for a Asian company for 15 years and although some of their stuff is very good quality, you never know when they may change something for the worse.

jts1957
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Aug 4, 2016, 3:57 AM

Post #9 of 12 (4255 views)
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Quote

I'm thinking the person that gave this TV to me had the brightness turned to Max

NOT brightness. The manufacturers ship them out with backlight intensity at maximum for the best picture. I'm sure they realize that doing this will also shorten the life of the set. No worries. They makeith more money when they sell people their replacement TVs. Crazy

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MJS60
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Aug 31, 2016, 4:23 PM

Post #10 of 12 (4114 views)
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Thanks again for the info! I was finally able to repair this TV by purchasing the LED's through AliExpress in Hong Kong. Took about 2 1/2 weeks but got 100 LEDs for only $7.00. Picture looks great and just like new now and I have some LED's left over for the next one with this problem too. Not bad for a free TV that was given to me. Cool

jts1957
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Aug 31, 2016, 4:47 PM

Post #11 of 12 (4108 views)
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Re: [MJS60] LG47LN5200 UB LCD TV [In reply to]	Can't Post

Turn the Back light intensity DOWN!

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Location: Far, Far Away

MJS60
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Aug 31, 2016, 5:02 PM

Post #12 of 12 (4100 views)
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Re: [jts1957] LG47LN5200 UB LCD TV [In reply to]	Can't Post

Done that, at 50% now and plenty bright.

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