LG 39LN575V Backlight down

[Daveatfernie]

Hi All,
I've just picked up this TV for £20 through facebook. The guy I got it from had said that the screen had just gone off. When I got it home I couldn't hear any inductive pop when I plugged it in so changed the fuse and it powered up.
When I hit the power button the tv comes on but there is no backlight.
I've never looked at an LED backlight before. Is it the same as a CCFL? Look for a powering 24V (or other voltage to watch for). Are they likely to fail as a set or a single led and finally if they've given up the ghost are they replaceable?
I only ask as I have a better set of tools at work and am limited to a multi meter at home. Is it worth me cracking off the back or a I better diagnosing with more of a tool set?

[ReeceyBurger123]

Re: LG 39LN575V Backlight down

Hi please watch the video linked in this thread:

https://www.badcaps.net/forum/showthread.php?t=52928

[Daveatfernie]

Re: LG 39LN575V Backlight down

Superb stuff thanks, looks like the psu and leds are not a bad price.
Very pleased with the set. I'll update with the repair.

[ReeceyBurger123]

Re: LG 39LN575V Backlight down

No worries, keep us updated on what you find

[Daveatfernie]

Re: LG 39LN575V Backlight down

Let me tell you a story about an inadvertent win.....
So needless to say I watched the vid (thanks very much for that they were nicely informative). I imagined that would be the problem as the PSU visibly looked OK. As I have a reflow station and a hot air gun at work I planned to repopulate the led with a spare.
Stripped the to down and got to the backlight. I disassembled each strip and powered them to find the faulty led(s) and all of them worked ok. :/
I reassembled the tv and realised that I'd forgotten to re plug the edge connector.
Disassembly
Plug in edge connector.
Reassembly
That wrapped up my lunch hour at work. (Cursing myself for not checking the PSU first)

The next day I fired up the set to check the voltage was ok on the board (helpfully labelled on the pcb for a change with both current and voltage rating) and I saw that the voltage blipped then came up steady. Strange.
Looked on the front of the to and the backlight was working fine.
I can only imagine that the was a thermally cycled connector inside it that had worked loose and re seating it sorted the problem as I've had the set on for 8 hours without a fault.

As you can imagine I'm chuffed to bits with my £20 tv and will be keeping this one for myself. The moral of the story being don't preempt the repair. Check the obvious first before you strip the set. Or throw logic to the wind, strip the set for no good reason and find you've inadvertently repaired the set anyway.

Thanks for the help.