LG 47LH55 Pictures problem

[budm]

I am working on LG 47LH55 with Horizontal lines and white screen after a minute on top of the pictures, so I did not see bad tab (press on them made no difference) on the panel yet, clean and re-seat the T-CON cable, no luck. There is no active components on the LCD panel board either, check MLC caps for shorts, no luck. I will be ordering new T-CON, TV is only 3 years old.
I check the LDO RT9183-12 (1.2V) check OK.
Another thing is that I did not find any Source/Gate drive for the TFT on the panel itself which is why I do not believe it is bad panel to have that many X/Y drivers to go bad on the whole screen.
I need to look up the spec on that large IC on the T-CON to see how it works.

[Mr Bill]

Re: LG 47LH55 Pictures problem

I had a Lg 47LH30 that the screen went bad. Tried 2 different tcons, and even a main board with no luck. If you unhooked one side of the tcon screen would be mint and the other had light lines in it. Put them together and it was a bad mixed drink. Whats the tcon board number? Might be the same as mine.

[budm]

Re: LG 47LH55 Pictures problem

My T-CON board is LC420/470WUF SBM1 SBL P/N 6870C-4100D.

[Mr Bill]

Re: LG 47LH55 Pictures problem

Your tcon is different. Mine only has one ribbon coming from the main board, my screen is a LC470WUE too. What were you checking on the small circuit boards that the tab bonds connect too? That would be my last and only resort to maybe see if a smd cap had failed before i crush the panel.

[budm]

Re: LG 47LH55 Pictures problem

I check for shorted out MLC (Multi Layer Ceramic, they tend to fail shorts circuits) caps. I also look for the Gate drives and Source drive IC's and I did not see any. Pressing on the tabs did nothing. So far nobody on the web has confirm that it is T-CON or panel problem, I see a lot of people with the same problem like mine.

[tibimakai]

Re: LG 47LH55 Pictures problem

try twisting the whole frame and see if it has any effect and you can exclude the panel then.
I have just found on my Vizio that I have a panel tab issue. When I twisted the frame, that dark spot from the center of the screen disappeared and the left side of the screen brightened up as well.

[budm]

Re: LG 47LH55 Pictures problem

I remove the whole frame to get access to all the tabs as shown in my pictures, made no difference. It looks like the X/Y drives are being told to be fully on.

[kunlok]

Re: LG 47LH55 Pictures problem

Any updates on this? I have a 47LH55 doing the exact same thing.

[budm]

Re: LG 47LH55 Pictures problem

Not yet, I had to put it away for now, I need to check the voltages on the side tab (Gate Driver). This seems to be common problem, and the T-CON did not fix the problem.

[budm]

Re: LG 47LH55 Pictures problem

I decide to work on this TV again since I am running out off room in my house.
I notice that I get loud squealing sound form the T-CON board by the two choke for the switching power supply and the IC was getting hot.
So I disconnect the right ribbon cable on the T-CON board (looking from the back, which will be for the left side of the screen-looking at the screen from the front) that goes to the LCD panel, the squealing stop and the right side side of the screen has normal picture.
I then start checking the voltage at the test points on the T-CON, what I found is that when the right ribbon cable is connected, the VGH voltage will go down from +22vdc (when the right ribbon is disconnected) to less than 1 Volt. I trace out the VGH connection, it goes directly to the IC on the top left (looking at the front of the screen) of the tab bonding flexible substrate.
So it has bad panel, I removed all the boards to be used for future repair.

[tom66]

Re: LG 47LH55 Pictures problem

Not yet seen a shorted LCD panel. Have you considered checking for bad MLCC near the tab drivers?

[wobbin]

Re: LG 47LH55 Pictures problem

I'd echo what tom66 has said about intermittently shorting multilayer smd capacitors. I've seen quite a few examples of this on Seimens AC motor drives - they might look perfect visually but take a soldering to one end and half the cap drops off !

[budm]

Re: LG 47LH55 Pictures problem

That was the first component (I know too well about MLCC) I always check when work on T-CON boards (found many in the past on broken T-CON boards and replaced many) and Tab bonding boards, there is no cap connected to this VGH line on the bonding board, the trace goes directly to the IC on the tab bonding board. I am not surprised that the IC shorted out. I was hoping for just shorted caps. This is the second screen (the other was 32" LG panel).

[wobbin]

Re: LG 47LH55 Pictures problem

Handy document, thanks for that

[lyubomirb]

Re: LG 47LH55 Pictures problem

I have the same problem but the opposite side is not working

[budm]

Re: LG 47LH55 Pictures problem

It is bad screen, I save all the boards, stands, speakers, etc, for spare parts