LG 32LB2R flickering horizontal lines

[Pappel]

Hi all!

I've been struggling with this TV for 2 days now and i can't seem to find the problem.

It had other issues when i got to it, first it wasn't turning on, kept blinking red light and after about 5 minutes it turned on. Once it turned on, there were big coloured vertical lines in sections on the screen. I took it apart and saw 2 bulged capacitors on the SMPS output side:

https://www.badcaps.net/forum/attach...1&d=1415359886

So i went on and replaced them. That fixed the power on issue and the vertical lines. However another issue emerged, when it had been in cold for some time then upon power on the whole screen was filled with colours on white background and loud static noise from speakers. Those lines and the static noise disappeared after about 2-5 minutes, probably due to warming up.
The image on the screen comes up ok, but the some flickering horizontal lines stayed and if listening closely to the speaker, static noise can still be heard. Also there is a buzzing sound somewhere on the SMPS board, source seems to be a relay of some sort, not entirely sure.
I'm suspecting the 450V 68uF filter cap is causing all this and since i have no equipment to test caps i'm gonna go ahead and replace that aswell, even tho it shows no signs of bulging or leaking. I also replaced all the caps on the output side.

image on screen (not entirely warmed up yet):
https://www.badcaps.net/forum/attach...1&d=1415360991

The amount of those lines decreases when it warms up, but some stay.
Any ideas? Thanks

[Pappel]

Re: LG 32LB2R flickering horizontal lines

Replaced the 450V 68uF filter cap, no change. I've now changed almost all the caps on the SMPS board, except the inverter output caps. I'm thinking it's not caps causing this but something else.. clearly somekind of signal noise. There is a 35V 470uF cap on the main board, located near the speaker outputs. Im gonna try to heat parts of the board and see if i see decease in time it takes to calm down the lines and static noise

[selldoor]

Re: LG 32LB2R flickering horizontal lines

Have you tried removing cleaning and replacing the lvds cable.
If it is a flat cable the contacts can be cleand with a pencil eraser

[Pappel]

Re: LG 32LB2R flickering horizontal lines

Checked all the connections, they're all ok. Also there is no flat cables in the system.
I'm suspecting that the component that is causing the ripple/noise is also responsible for the blown caps that i replaced in the output section.
Can the output schottky diodes act like this? Because it seemed like heating the area where the blown caps are, made the flickering calm down quicker, behind those caps is the diode.

[Shinju]

Re: LG 32LB2R flickering horizontal lines

^ I can tell you there is, look at your T-con board with the shield off.

Here is your panel and possible t-con

http://www.hostingpics.net/viewer.ph...0531210428.jpg

thread about your panel

http://www.teleservice-depannage.com...us-d-image.htm

[Pappel]

Re: LG 32LB2R flickering horizontal lines

Ooh, new information! I'm by no means an expert at TVs, didnt even think of looking behind the metal shields. Will get right on it and post my findings or results.
Thank you!

[Shinju]

Re: LG 32LB2R flickering horizontal lines

Its how we learn and help one another! I am no TV expert either!

[Pappel]

Re: LG 32LB2R flickering horizontal lines

Well i did clean the t-con board flex cables but i dont have time to assemble it today.
But i just thought it's kind of a long shot, wouldn't explain the static from speakers...
will continue tomorrow

[Th3_uN1Qu3]

Re: LG 32LB2R flickering horizontal lines

Since the noise in the speakers is correlated to the lines you see on the screen, this is most definitely still a power supply issue.

Capacitors do not need to be bulged to be bad. I would replace all power supply capacitors on the 5V rail. That powers all the logic, including the signals in the mainboard, t-con board and so on. Some do use 12v and have a built-in 5v regulator, but most of them run off the 5v main rail.

Also it is the 5v rail which needs tighter regulation, so the feedback of the SMPS is usually taken from the 5v rail. This means that any garbage appearing on the 5v rail will get magnified on the other rails, which explains why you hear it in the speakers as well.

[tom66]

Re: LG 32LB2R flickering horizontal lines

Long time since I did this one, since the majority of the load is on the 24V the 24V is where the feedback comes from (I -think-), the 5V rail is just the standby rail (separate supply), 3.4V is buck'd from the 5V rail with on/off signal, 6.5V is also buck converted. 19V is for audio from memory, it is not regulated and has about 1V variation with backlight brightness, but the class D regulator has good CMRR so it's ok.

It's an oddly complicated power board. Mine had bad 3.4V converter, low output causing various bugs - audio included, although the audio was replaced with silence and loud occasional random bursts of noise. Also randomly stuck in standby & side buttons intermittent.

Noise could be in 3.4V or 19V rails.

[Th3_uN1Qu3]

Re: LG 32LB2R flickering horizontal lines

Tom's the man once more... I think he fixed about as many kinds of TVs like i did laptops, so listen to his advice.

[Pappel]

Re: LG 32LB2R flickering horizontal lines

If it's the 19V rail, shouldn't it affect the backlight aswell since it runs from the same rail? Unless the fault is between the octocoupler and the 19v output

https://www.badcaps.net/forum/attach...1&d=1415453036

This optocoupler or the 35V 47uF cap maybe?


Also the blown caps and the noise source must be related since the lines or static from speakers weren't there before the TV died, so either the caps blew because of the noise or the blown caps were responsible for the fault in component causing the noise. just a thought..

[tom66]

Re: LG 32LB2R flickering horizontal lines

No, the 24V rail is used to run the backlight. Unregulated 19V could cause issues with audio without causing issues with the backlight.

[Pappel]

Re: LG 32LB2R flickering horizontal lines

There isn't much going on on the 19V rail after the optocoupler that also feeds the inverters. some SMD resistors, diodes, zener diodes

marked the trail with red
https://www.badcaps.net/forum/attach...1&d=1415459228

[selldoor]

Re: LG 32LB2R flickering horizontal lines

I dont know but perhaps check for AC - leaky diodes?

[Pappel]

Re: LG 32LB2R flickering horizontal lines

I found a shorted diode...


or not... have to check them out of the circuit

[Pappel]

Re: LG 32LB2R flickering horizontal lines

I haven't been able to find anything, all the diodes seem ok. I'm gonna go ahead and replace the little 35V 47uF, 50V 33uF and 50V 4.7uF caps aswell.
Also, do the output schottky diodes suppose to get that hot? The heatsink gets very hot.

[gonçalo gomes]

Re: LG 32LB2R flickering horizontal lines

essa avaria e condensadores na main board

[CroTech]

Re: LG 32LB2R flickering horizontal lines

Hi guys... Got the same TV, a new project.

The same problem occurs when I turn on my TV. After some time when the TV
heats up, the flickering lines tend to disappear but still there are some of them.
Tomorrow morning, dissembling it, replacing every cap on the main board and then testing further and reporting here.

I hope for your help if I get stuck somewhere.

All you guys helped me before, especially tom666 and selldoor so I have to say I am
in your debt and very thankfull.

[CroTech]

Re: LG 32LB2R flickering horizontal lines

Replaced every cap... There was only one blown so I oversized it and changed it from 1000uF 16V to 1000uF 25V. The problem still persists and it even gets worse sometime as you can see in the pictures below. I cleaned the flat cable contacts that go to the T-CON oard.

I presume the problem is with the T-CON board?