LG 55LF5610 panel fault?

[leerumbles]

Hi all,

I was hoping someone might be able to tell me whats wrong with this LCD TV or point me in the right direction. I don't know the history of this TV. It came from a friend who acquired it from their place of work with this fault.

There is a horizontal band across the top of the screen which appears to be unaffected but below this band the screen has horizontal black lines. After a minute or so the screen progressively gets saturated in yellow / orange colors which moves with the images displayed on the screen.

I have replaced the tcon and AV board but unfortunately that didn't work.

The panel its self is unlike one I've seen before. Rather than the normal source / gate drivers, this panel only appears to have drivers on the bottom of the panel.

Having read many of the treads here, I have examined the flex cables from the panel to the driver and there is no obvious faults. I have applied pressure to the bonds in hope to find a loose connection but to no avail.

Any advice would be appreciated.

[budwich]

Re: LG 55LF5610 panel fault?

depending on the design, you can only see the side tab drivers with the front bezel removed.

Anyway, it is likely a "panel failure" (ie. tab issue). You can check this further... if you look at the edge boards at the bottom of the panel, they may have "interconnection ribbons" going between the boards on each side of "center"... ie. there is two edge boards on one side of the panel and two on the other. The ribbons are "unclampable" / removable to allow disconnection of the edge boards (not from the panel but from each other). If you unclamp / disconnect one and see what happens to the picture there after. go from there. Note: don't play with the connectors / cable while powered.

[Charleyd]

Re: LG 55LF5610 panel fault?

I have a LG 55UH6030-UC (2016 model) that has an intermittent screen problem that I suspect is a problem with the gate drivers, and this TV definitely does not have side tabs. (I have removed the front bezel.)
[I have another TV (a Philips) that I also suspect has a problems with the gate drivers and also does not have side tabs. So this is a real thing.]
[See page 36 of this presentation that shows the evolution of gate driver construction:
I have been reading about panels that have the gate drivers incorporated onto the glass itself. The shift registers and output transistors of the gate drivers are deposited onto the left and right edges of the display at the same time that the switching transistors connected to the LCDs are fabricated. I have seen this type of integrated gate driver circuitry called "gate driver monolithic" (GDM) circuitry. I would like to learn how this works to figure out if a failed gate driver can be isolated in a manner similar to how side tabs with failed drivers are torn off to get them out of circuit.
leerumbles - maybe my idea can save your TV too.

[budwich]

Re: LG 55LF5610 panel fault?

IF there are no side tab / drivers visible (yes there are designs like that), then as suggested. another test is to disconnect the interconnection ribbon between the bottom edge boards. IF those don't exist, then the other alternative is to use the "tape cutoff" method which uses a piece of tape to "cutoff" the connection at the tcon card (on the connectors for the cables going to the panel). Lots of posts on this method both here and on the internet.

Ultimately, you need to determine which side is the problem... that's what "disconnect tests" do. One other test is to disconnect, one at a time, cables going from the tcon to the panel. Go from there.

[Charleyd]

Re: LG 55LF5610 panel fault?

I have tried operating the TV with just the left or just the right cable going from the tcon to the panel connected. The TV was connected to a source. This is where I really need some advice:

_____________________LEFT_________RIGHT
Right ONLY connected___White_______No image
Left ONLY connected___Vert Lines*_____White
Both connected________Normal_______Normal
("Left" and "Right" always as-viewed from the front.)

* The screen was dark but with six, evenly-spaced, single-pixel lines. I believe that these were the left-most pixel columns of each band corresponding to the six flex ribbon cables on the left half of the panel. The lines are of different colors (The colors are fixed, but each of the six lines are different.).

I guess that the next thing to try is the tape cuttoff method. I believe that I can figure out which of the lines on the flat connectors between the T-Con and the panel carry the gate driver signals.

[Charleyd]

Re: LG 55LF5610 panel fault?

Some additional info (and maybe a bit of progress on the diagnosis front): I did some extended testing with just one or the other of the flat cables between the T-Con and the panel connected. With the LEFT only (and BOTH) connected, the "intermittent screen problem" that the TV has (and that I have not described as of yet) occurs AND the Main Board heat sink gets very hot. With just the Right side connected, no screen problem and the Main Board stays relatively cool.

[budwich]

Re: LG 55LF5610 panel fault?

"normally", disconnecting a tcon to panel cable will show a white screen on that side (no image, signal but screen is white because of "panel voltage" allowing LCD pixels to transmit backlighting).... so I would have expected a display on the right and white on the left in your first "test". Are you sure of your source?

Next "test", the set is now trying to drive what appears to be the "bad side" and the other side is now a "happy white". On sets where the main board switches voltages for the tcon which then go to the panel, the main board is then going to "see" any "drive issues" which may take out the main board so I wouldn't run things too much until you find a way to address the "drive problem".

I am not sure what you are trying to say with your third "test", everything "normal", what's the problem?

[Charleyd]

Re: LG 55LF5610 panel fault?

The intermittent screen problem with the LG 55UH6030-UC TV is that, intermittently, there will appear a brief, single pixel, bright horizontal line and then the screen will go blank for a second or two, sometimes longer. The backlights stay on throughout. There is no rhyme-or-reason as to when or how frequently the display will go blank. Sometimes the picture will be fine for a good while, and then it will start blanking out at 8- to 10-second intervals (really annoying). The location of the bright, momentary horizontal line is usually different every time it appears. The other notable symptom is that the Main Board runs super hot. It has a large, aluminum heat sink over a significant portion of the Main Board and it gets too hot to touch. The screen blanking will often start right away when the TV is turned on, so it does not seem that it is caused by the Main Board getting hot. (More like getting hot is a symptom of some other problem.)
So with both T-Con-to-panel cables connected, you get good video but with intermittent bright-horizontal-line-followed-by-blank-screen (Let's call this a "glitch".) and a very hot Main Board.
Right cable only connected gives no image of any kind on the right (just a glow from the backlights), white screen on the left, no glitch, and cool running Main Board.
Left cable only connected gives a few, single-pixel vertical lines and otherwise dark screen on the left, white screen on the right, with the glitch, and hot running Main Board.

[leerumbles]

Re: LG 55LF5610 panel fault?

Thank you both for your input. It appears that there is no interconnecting ribbon between the bottom left and right driver boards. The only thing that links these together is the tcon board. Image attached.

I removed the left and right ribbons one at a time from the tcon board and was surprised to find the same fault (but only on one half of the screen) regardless of which ribbon is connected / disconnected. Images attached.

I was going to try the "tape cut off" method but as it currently stands, it appears that both the left and right drivers are effected with an identical fault which may be the case but it leads me to believe the fault may lay elsewhere?

Please feel free to correct me if I've misunderstood.

[budwich]

Re: LG 55LF5610 panel fault?

try cleaning / reseating the lvds cable running from the tcon to the main board.

[Andrew F. Ali]

Re: LG 55LF5610 panel fault?

If you have done some reading on the 'cut-off' method then give it a try. Just be patient as it takes a lot of trial and error, but you will get there.