LG 47LN5400 TV Backlight problem

[jason123]

Re: LG 47LN5400 TV Backlight problem

New here and would appreciate the help. I am running into the same problem as 99% of the LG TV owner population.. Sound ok, but no picture. I believe one or more of the backlight LEDs are shorted. I would like to replace the LED(s), but doesn't anyone know the specs or part number of the actual LED part number? My TV is the LG 47LN5400.
I have seen sites that sell repaired strips for more than the TV is worth, so I'm trying to replace the LEDs myself.

[NormL1]

Re: LG 47LN5400 TV Backlight problem

I have a LG 47LN5400 that I am attempting to repair. The Power supply board is PCB: EAX64905501(2.2). Along with many others I have found there is an image when you use a flash light and audio sound but the tv does not have back light. I Completed a careful disassembly using a youtube video https://www.youtube.com/watch?v=Bf5T2wwtydY. I found that some of the LED's were defective. I purchased some LED's off of Ebay by searching SMD 3528 ultra white light diode. I replaced the LED's that were shown to be faulty using the techniques in the youtube video. Placing 3v I could trigger on one LED chip. With a 9v battery I could test 3 LED's in series. and with 24v I could test a full strip. I put the tv together and tried it. A quick flash of backlight then black followed by audio. I retested the led strips and found more LED's on that sring were faulty. I replaced the faulty LED's but after retesting I only had more shorted LED's. I switched my attention to the Power supply. All primary voltages are good at P601-P0608. On the secondary side I have have replaced C802,C0801, C0805 and C0806. I tested D253 and D252. Replaced C257 and C258. I have replaced Led driver IC801 and Mosfets Q803 and Q806. Still my Back light issue persists. Does anyone have a schematic or know where I should look now for the fault?
Thanks

[RobbieC]

Re: LG 47LN5400 TV Backlight problem

Have you worked your way along all of the strips confirming they all light up ? I had a similar issue and while many of the led's failed in shorted mode, one failed as open circuit with a noticable burn on the lens. As it was open it prevented the whole string from lighting. My quick resolution was to short it which meant the rest then illuminated.
Not a great fix and has since died again (yet to determine whether additional led's have failed or my short)
Also, thought these strips were 3535 leds although no-one seems to know full spec so will be very much trial and error

[SurrealMustard]

covering bases

So just to recap, what kind of Leds are recommended for these sets? Also, can they be tested without a bench power supply?

[ReeceyBurger123]

Re: covering bases

So just to recap, what kind of Leds are recommended for these sets? Also, can they be tested without a bench power supply?

Check out my video:

https://m.youtube.com/watch?v=RxwdC7V5Ue0

[SurrealMustard]

multimeter hack! :-)

Check out my video:

https://m.youtube.com/watch?v=RxwdC7V5Ue0

Interesting. So the multimeter will be enough to test the existing lamps, which will be helpful. If I don't currently have a television with a dead panel, could I just go and buy any LED-backlit LCD with a cracked screen from Craiglist for a few dollars and expect the Leds to work? If not, where would be a good place to get replacements?

[ReeceyBurger123]

Re: LG 47LN5400 TV Backlight problem

The craigslist one will be fine and will mean you have other replacements on hand.

[SurrealMustard]

good to know

The craigslist one will be fine and will mean you have other replacements on hand.

That's good to know. What if nobody is selling or giving away any cracked LED-backlit LCDs locally? Can the Leds be acquired any other way?

[Malachi]

Re: LG 47LN5400 TV Backlight problem

I'm here in Ohio. I have a full set of LEDs to a backlit Emerson that I cracked the screen on. Lol.

[SurrealMustard]

inquiry

I'm here in Ohio. I have a full set of LEDs to a backlit Emerson that I cracked the screen on. Lol.

Would you be willing to sell them? Will they work with the LG?

[Malachi]

Re: LG 47LN5400 TV Backlight problem

Yes. They are listed on eBay. I don't know if I'm allowed to link to it here.
I have them listed for what I paid for them. $70.
Sent you a pm.

[SurrealMustard]

ah ha!

Well, I finally disassembled the panel. Take a look at the first picture and see if you can guess what the problem might have been .

It was obviously pretty seriously burned, but after doing the infamous "scratch n sniff" test with a multimeter, I found various other leds on the board that were shorted and one or two that weren't, but were in the process of dying. I'll probably buy two strips on eBay - one to replace the one that completely fried and one to extract Leds off of to replace the other dead modules on the other strips

[ReeceyBurger123]

Re: LG 47LN5400 TV Backlight problem

Holy shit ! I think that Led is bad right ? Yeah you will need to also repair the return line trace (small trace next to it) that it burnt if not you wont get any Bl still. Keep us updated on what happens. Would have never expected one to get that bad though it must have gotten very hot.

[CapLeaker]

Re: LG 47LN5400 TV Backlight problem

I guess you found it no problem!

[SurrealMustard]

Flaming hot Leds

Holy shit ! I think that Led is bad right ? Yeah you will need to also repair the return line trace (small trace next to it) that it burnt if not you wont get any Bl still. Keep us updated on what happens. Would have never expected one to get that bad though it must have gotten very hot.

I guess you found it no problem!

You got that right! And on a <2 year old set too. I mean, that papery layer that goes around the backlights is exactly that - paper. This thing could've burst into flames. You'd think that being cut a break in not having to source CCFL lamps for their flatpanels anymore that manufacturers would at least get quality Leds, but apparently not.

Anyway, the plan for this one will be to buy two L2 strips. One to replace the strip that was obviously burned, and the other to extract Leds off of to repair the handful of other Leds on the other various strips that have shorted out (but not yet started the television on fire).

[ReeceyBurger123]

Re: LG 47LN5400 TV Backlight problem

Yeah, its plastic but as you said the same thickness of paper so it could potentially set fire. Also do you they would bother putting good leds in their Tv's, really ? They wont because that way they make less profit and Tv would last longer meaning that well it wont fail as quick so people wont have to buy another off them. Its a total joke the way everything is going all cheap crap that doesnt last. If its not the Leds its the Lcd glass which is not fixable.

[Malachi]

Re: LG 47LN5400 TV Backlight problem

I like the way Reecey talks as if he is 60 years old. Lol.
Things have been made cheaply and like crap since before you were born.
I didn't have a color TV till 1982. ��
Do you know what a rotary phone is? Lol

[ReeceyBurger123]

Re: LG 47LN5400 TV Backlight problem

Lol I know how these people/compaines work all of them are greedy sly bastards like almost everyone now a days. Whats a rotor phone too ? Narr just messing

[CapLeaker]

Re: LG 47LN5400 TV Backlight problem

I like the way Reecey talks as if he is 60 years old. Lol.
Thinks have been mad cheaply and like crap since before you were born.
I didn't have a color TV till 1982. ��
Do you know what a rotary phone is? Lol

Lol

[SurrealMustard]

(Led) Strips!

Update: Led strips have been ordered. We should find out how well this'll work either late this week or early next week.

Yeah, its plastic but as you said the same thickness of paper so it could potentially set fire. Also do you they would bother putting good leds in their Tv's, really ? They wont because that way they make less profit and Tv would last longer meaning that well it wont fail as quick so people wont have to buy another off them. Its a total joke the way everything is going all cheap crap that doesnt last. If its not the Leds its the Lcd glass which is not fixable.

Fair enough. They actually hit the mark perfectly on this one in that case: catastrophic failure (most folks would be too afraid to completely dismantle their flatpanel like this) just outside the 1 year warranty period. Bonus points if the customer buys another LG to replace it.