LG 60UH8507 Backlight turns off after few seconds

[FrozenHaxor]

Hello, this TV is a relatively new platform, certainly new to me. LED backlight connection is unclear to me, appears to be several separate circuits going to the ribbon, instead of the more common 2 wire connection and everything in series.

Anyway the problem is that the TV turns on and works just fine, then after 10 seconds or so the backlight turns off, but you can still make out the picture so the rest is still working. There is some sort of diagnostic LED on the power supply that blinks red 4 times in a loop with pauses after the backlight failure occurs. Couldn't really find what this means. In fact I couldn't find much info about this particular TV at all.

Any directions on where to go? There appears to be a test point on the power supply marked LED+ and GND. The voltage is 45V after plugging the PSU into the mains, then it falls to 42,5V in standby. After turning the unit on, it goes to 87V, LED backlight comes on, works for about 5-10 seconds and then the backlight turns off, but the voltage on this point still stays at 87V and begins to fall off very slowly down to 62,5V and the power supply blinks the diagnostic LED 4 times and repeats it.

I would really like to eliminate all possible causes before disassembling this massive 60 inch panel to get to the LEDs.

I do posses a high voltage LED backlight tester.

Attaching pics of the inside.:

[FrozenHaxor]

Re: LG 60UH8507 Backlight turns off after few seconds



I have tested each VC_ to LED+ on both ribbons and I get stable 75-80V @42mA. Not sure how else I can test the backlight without disassembly.

I'm swaying towards the power supply being faulty.

[dick_barton]

Re: LG 60UH8507 Backlight turns off after few seconds

It looks like you have a led problem. Turn the set on and reduce the backlight level to 50% or less and see if the backlights stay on longer.

[FrozenHaxor]

Re: LG 60UH8507 Backlight turns off after few seconds

Backlight stays on at maximum power saving settings where the image is barely visible.

[dick_barton]

Re: LG 60UH8507 Backlight turns off after few seconds

Backlight stays on at maximum power saving settings where the image is barely visible.

So turning backlight to minimum they stay on but the image is barley visible. It certianly appears that you have a led problem.

[FrozenHaxor]

Re: LG 60UH8507 Backlight turns off after few seconds

Alright then. Looks like the inevitable is coming. Disassembling the panel now.

[dick_barton]

Re: LG 60UH8507 Backlight turns off after few seconds

That's a large panel to remove. There are threads on the forum offering advice on removing large panels. Good luck.

[FrozenHaxor]

Re: LG 60UH8507 Backlight turns off after few seconds

Manage to disassemble it from the back. Panel is still lying on the table, I lifted the back away with suction cups after removing all screws. Looks like it has edge LEDs on the bottom only, two strips on metal backing glued in. Needs some heat to loosen them up.

[FrozenHaxor]

Re: LG 60UH8507 Backlight turns off after few seconds

Right, one diode is faulty. Decided to order the whole heatsink with diodes already glued in. Not feeling like having to deal with this TV again if another diode fails after replacing just one. Will update on the topic when I get the part and the panel back together.

[Andrew F. Ali]

Re: LG 60UH8507 Backlight turns off after few seconds

I would suggest you change ALL the backlight strips, instead of the single bad strip. This will guarantee not having to open her up again for along time. Remember to turn down the Backlight setting on ALL the Inputs after you close her up. 65-70% is about the best setting. Good Luck.

[dick_barton]

Re: LG 60UH8507 Backlight turns off after few seconds

Right, one diode is faulty. Decided to order the whole heatsink with diodes already glued in. Not feeling like having to deal with this TV again if another diode fails after replacing just one. Will update on the topic when I get the part and the panel back together.

Good job and good decision to replace the whole strip.

[FrozenHaxor]

Re: LG 60UH8507 Backlight turns off after few seconds

The entire backlight was replaced along with the radiator it's factory bonded to. TV works fine now. Thanks for the help to everyone involved in the topic.

I see now why this one was so difficult to diagnose. The power supply has the ability to address individual backlight strip sections depending on current display content. Very different to regular fixed ones.

[dick_barton]

Re: LG 60UH8507 Backlight turns off after few seconds

Glad you got there in the end.

[vikivng]

Re: LG 60UH8507 Backlight turns off after few seconds

hI gus ,
I hope its ok to add to this thread.
I have a 55 Toshiba tv that seems to have similar symptoms to the OP,
If the tv is on without any peripherals attached and no menu input, it will stay on indefintely.
From the time the menu button is pressed, the backlights go out.
If anythng is connected via hdmi, the backlights go out.
I have changed the mainboard to no avail.
Does this point to the leds.?

[nomoresonys]

Re: LG 60UH8507 Backlight turns off after few seconds

I usually try the simple things first, firmware update and factory reset, might not fix it but shouldn't hurt and can eliminate those from the suspects after.

[EuLE]

Re: LG 60UH8507 Backlight turns off after few seconds

Recently, my TV (LG 60UH8509) had this exact symptoms after 3 years of usage. The backlights would go off after 5 seconds and
LD701 on the powerboard was blinking in intervals of 4 times. The TV had sound and by shining a light onto the screen you could see the lcd had a picture.

First thing I did was buy a new powerboard via the LG website and exchanged it. Unfortunately this didn't fix it so I went ahead
and opened the panel to get to the leds. Turned out one of them was faulty so I ordered 2 new strips from AliBaba as it was the only source I could find.

After reassembly when I first turned on there was no picture at all, so I reopened the back panel and reconnected every flatband cable connection to the LCD.

Now my TV works perfectly again. The next step is to make sure the max value for the backlights is set to 70% in every picture mode.
I'm quite sure this should prolong the LEDs' life by a good amount of time.

So all in all I paid around 290€ for the parts (powerboard 180€ + led stripes 110€),
but I'm sitting on a spare powerboard now. I'm still undecided, but If I sold it, I could realistically get maybe 100€ or so.

Last point: the LG support was not helpful at all. All I got from them were pre-made e-mail texts saying "no support for self service" and such things. "Go buy a new TV" ... after 3 years ... sure, LG

Word of advice: Don't underestimate the space you need when disassembling a 60" panel.