LG 79UB980T Video problem

[sushi1]

hello,
i've been having a problem with my LG 79UB980T, there's no picture visible in all the inputs (only vertical lines with a usually pink background flickering), tried satellite receiver, Xbox One, movie from a USB Harddrive & PS4. even the built-in youtube app and netflix show no videos.
however i can see the menus with flawless full colors and listen to sound perfectly, it only appears when anything is played.

*I use only high quality hdmi 2.0 cables. (if it matters)
*I once used cheap HDMI splitter

I thought it might be a T-Con issue at first but the TV worked perfectly for two days after changing it's location (weird i know), then the issue came back.

So I opened the TV, jiggled the wires and connections a little bit, nothing happened, the boards look perfectly clean and no signs of burnt up capacitors or stuff like that.

What could it be?

Pic attached.

thanks

[Andrew F. Ali]

Re: LG 79UB980T Video problem

Well I am tempted to say put it back where it worked before....But I think this is aT_CON issue.

[sushi1]

Re: LG 79UB980T Video problem

It is in the same place ever since, I just covered the screen with a bedsheet.. My question is.. how do I know for sure it's a T-Con? does the T-Con distinguish between the menu screens and whenever a video content is played? because as far as I know, if it was T-Con related, these vertical lines would be all over the menus as well? Correct me if I'm wrong

[sushi1]

Re: LG 79UB980T Video problem

Another question, assuming it's a faulty T-Con, how can it possibly get fixed by itself for a couple of days?

[diif]

Re: LG 79UB980T Video problem

I'm guessing there are two processors on the mainboard, one does the menus and there is another to do image processing, this one had BGA issues.
It sometimes only takes a light press on the processor to make/break connections (bring the picture back) so it's possible moving it caused it to temporarily work.

[sushi1]

Re: LG 79UB980T Video problem

Exactly what I had in mind, So that's a Main board issue, not T-Con?

[Davi.p]

Re: LG 79UB980T Video problem

Excuse me you have a 79 inches so you probably rich and you can't carry it to a service center? Or you want a diagnosis just to be sure? Attempting a self repair on beast like this is risky... For me is impossible tcon, is surely Mainboard, what exactly i don't know, 'cause i don't know the model... Since the location change story i agree with bad bga soldering, the problem seem to be video decoding, so maybe a certain RAM chip bad soldered.

[sushi1]

Re: LG 79UB980T Video problem

I am not attempting to repair it myself, I just want diagnosis because I am in a country where technicians cannot be trusted.

[sushi1]

Re: LG 79UB980T Video problem

I found several main boards online that exactly match the one that needs replacement, same board model no. but not taken from the same TV size as mine. they're either taken from 65" or 84" models while mine is 79"
(does the TV size matter?)

I need someone to point me in the right direction for selecting a compatible board.

mine is EAX65608604(1.1)

took a couple of pics of the board

[Davi.p]

Re: LG 79UB980T Video problem

The size matters.. you can become to a video not comprensible due to different incompatible brand of lcd panel, i think is possible by a technician but it must do some steps more (copy of eeproms, firmware flash)...

[sushi1]

Re: LG 79UB980T Video problem

It worked again after leaving it turned off for nearly a week.. this time without changing places, weird right?
Im currently waiting for a new main board to be delivered, but i'm lost here.
Why does it work after being turned off for a few days? bad soldering? bad PSU? corrupted software?

[koka0011]

Re: LG 79UB980T Video problem

check gamma voltages

[sushi1]

Re: LG 79UB980T Video problem

I doubt that's the culprit since menus are clearly visible, but will look it up just in case.

[Davi.p]

Re: LG 79UB980T Video problem

Gamma voltages?? Why? it's unuseful for me... bad soldering of the cpu is the main suspect, you can provide your mainboard to a reballing service or buy a new mainboard.
But you've bought a new MB so if doesn't work the minimum you can do is to let someone copy the content of the setting eeprom of the old MB to the new MB (or a chip swap) and after try to upgrade with a firmware for the model that the new MB come from. BYE.

[sushi1]

Re: LG 79UB980T Video problem

* the TV works fine after leaving it turned off for a couple of days.
* it will continue to work flawlessly ONLY if I left it switched ON (can leave it 10 hrs no problem)
* if I switched it OFF even for 1 sec. and turn it back ON the issue comes back and I have to wait another couple days for it to work again.

I am still waiting for a new mainboard to arrive but in the mean time,
I am really intrigued what would cause this mind bending issue.

*I know Bad BGA soldering is the main suspect here,
but I have this feeling, it can be caused by another really small / dumb issue.

can it be something else?

*Sorry for asking many questions, I know I’m a bit annoying, but the TV is driving me crazy.

[Davi.p]

Re: LG 79UB980T Video problem

Another source of possible problems on the mainboards are power mosfets or linear voltage regulators but its difficult to put them in relationship to the behaviour of the defect. It quite strange, it seems something involved only in the startup that works better warm, i dont know which one. Maybe something that holds settings information like the eeprom or the startup software like the flash spi if present..

[sushi1]

Re: LG 79UB980T Video problem

How about an EEPROM reset?

[Davi.p]

Re: LG 79UB980T Video problem

No good idea, unuseful for me..

[sushi1]

Re: LG 79UB980T Video problem

okay, popped in a new main board and the TV worked fine..
thanks for your help


What I am really concerned about is if the new main board will adapt well to 220v power instead of 110v? since I bought it from the US while I’m in a different region.

It’s the exact same board no. but was taken from a TV that was working under 110v
thanks