LG 49UJ6500 LCD panel lighter band that goes away

**kasfamily** · 02-19-2023, 01:16 AM

Re: LG LCD panel lighter band that goes away

Try to disconnect the harnesses going from the main to the matrix in turn. Will there be this stripe on each of the halves of the screen.

**howardc64** · 02-19-2023, 04:12 AM

Re: LG LCD panel lighter band that goes away

Looking at the screen

Left side T-Con flex removed (white stickered flex)

Right side T-Con flex removed (red stickered flex)

When plug both T-Con flex back in, only right side shows band. Eventually becomes faint and disappears after few min.

Looking closer at the band with magnifying glass shows its pixel color error. So maybe t-con section on the main board

**Diah** · 02-19-2023, 04:32 AM

Re: LG LCD panel lighter band that goes away

its not easy to find the fault at MB T-CON circuit which caused this.
but try heating with hair dryer several point at MB. or use pressure with finger at heat sink... and remark any change.

or try to make carefully pressure on the Bezel corner where the issue appear.. see any change.

**Davi.p** · 02-19-2023, 07:25 AM

Re: LG LCD panel lighter band that goes away

The fault is mostly on the panel's gate drivers, are them of COF type? Therefore side tabs?

**howardc64** · 02-19-2023, 11:26 AM

Re: LG LCD panel lighter band that goes away

Hair dryer heat sink area near T-Con connectors and turn-on TV. Perfect pixels at the top so definitely thermal related on main board.

I'll try reflow next. Have pre-heater, good hot air station, no residue flux for BGA reflow and toaster oven (haha). Toaster oven has been the easiest in the past... less chance of over heating but I guess stresses the whole board.

**howardc64** · 02-19-2023, 01:39 PM

Re: LG LCD panel lighter band that goes away

Reflowed. Seems to make no difference. Hair dryer different parts of main with heatsink off, no difference.

When remove both T-Con connector from main, sometime lines/band appear and repeatedly do this while power cycle. Sometimes no line/band appear and repeatedly do this while power cycling. Gently pressuring upper panel corner doesn't change top lines/band.

Strange.

**Davi.p** · 02-19-2023, 03:09 PM

Re: LG LCD panel lighter band that goes away

you must remove screen bezel as i have said..

**howardc64** · 02-19-2023, 05:22 PM

Re: LG LCD panel lighter band that goes away

Originally posted by Davi.p

you must remove screen bezel as i have said..

4K panel, no side COF tabs. Took off bezel

Gently pressed upper corner and all along left and right edge.
Pressed panel bottom COF tabs on panel and on driver board.

No difference.

Tried taping both T-Con flex connector in various locations. No fix.

**howardc64** · 02-19-2023, 08:19 PM

Re: LG LCD panel lighter band that goes away

Looked up Apple 27 LG LCD bright line problem since its common. A poster comment its from IPS overbias

https://www.ifixit.com/Answers/View/...ears+in+corner

This LG TV is IPS panel so decided to run the following youtube IPS panel exerciser

https://www.youtube.com/watch?v=BFUv...0jimbojones000

Stopped the video @ 20min. Solid bright colors would have brightness flicker afterwards (not my eye, wasn't looking at the test before turn it off) which eventually steadied. Turn off the TV for an hour and back on, lines are gone! Only changes are

Heat sink back on main board with 2 spring clips
Ran IPS video exerciser

Turn it off and back on after 20-30min. No more lines...

Put the rear TV panel back on, moved to different room. Lines are back.... But of course lines fade after running the TV for a few min. Perhaps I'll just leave it this way.

Strangest problem.

**howardc64** · 02-20-2023, 12:32 AM

Re: LG LCD panel lighter band that goes away

Think I finally found the failure and non failure mode. it is EXACTLY same as 2009-11 Apple 27" LG IPS screen failure mode.

If TV is plugged into the wall but powered off. After a couple of hours, no more lines on future power-on

If TV is unplugged for just a few min. Next power on will have lines.

This is similar to my Apple 27" IPS screen experience. I have seen many all with same behavior.

This behavior is the cause for confusion while diagnosing this problem. Power connection is constantly being unplugged during various disassemblies and test while chasing various suspected causes. I only discovered this after stopped assembly/disassembly/moving the TV which all required unplugging the PSU.

Anyway, don't know why but these LG IPS panels is either getting some power or avoid discharging completely with the TV plugged in but powered off.

**Davi.p** · 02-20-2023, 07:33 AM

Re: LG LCD panel lighter band that goes away

You are probably lucky, try replacing the electrolitic caps on main board, or if you have capacity/esr tester test them.. you can also try to leave tv unplugged for an hour, then heat those caps with hair dryer then turn on tv..

**howardc64** · 02-20-2023, 10:00 AM

Re: LG LCD panel lighter band that goes away

Originally posted by Davi.p

You are probably lucky, try replacing the electrolitic caps on main board, or if you have capacity/esr tester test them.. you can also try to leave tv unplugged for an hour, then heat those caps with hair dryer then turn on tv..

I previously did heating test without success. But can give it another try now I have clear solution to repair the lines. Have tested the solution a few times already.

Besides likely cause due to simply aging. Another possibility is the LG IPS panels might also get this problem by the slight bending when lifting the LCD panel out and reinstalling. The panel was carefully remove with suction cups and place it on a clean surface.

Besides about 5mm of lines across the top edge of the LG TV panel, I also noticed ~1 pixel horizontal line about 15mm long ~5cm below upper right corner. If my "bending" theory is correct, this is the corner I lifted slightly to confirm lines on panel rather than backlight system. All of these lines disappears after plugging TV into the wall for about 2 hours.

Its hard to verify this theory because panel removal is usually attempting to fix some display problem already such as backlight system. Therefore, its hard to confirm the problem was not there prior to removal and the unavoidable slight bending of the LCD panel during removal. In future efforts, I'll attempt to verify this.

**Davi.p** · 02-20-2023, 11:11 AM

Re: LG LCD panel lighter band that goes away

Hair dryer heat sink area near T-Con connectors and turn-on TV. Perfect pixels at the top so definitely thermal related on main board.

your words..

**howardc64** · 02-20-2023, 11:26 AM

Re: LG LCD panel lighter band that goes away

Originally posted by Davi.p

your words..

Yes, unfortunately later attempts didn't work (post #7). So its strange. This is before I discovered real problem+solution by plug into the wall. Maybe first hair dryer attempt waited long enough after plugging into the wall and the later attempts did not?

Also failure seems to depends on image color. Sometime it shows on dark image and sometimes no. Most times it shows on mid bright image. It disappear on too bright image.

Many variables. So far only definite solution is plug into wall for few hours

If I just unplug for few min, lines will appear again.

**Davi.p** · 02-20-2023, 12:14 PM

Re: LG LCD panel lighter band that goes away

have you got a capacitor meter? the test is fast

**howardc64** · 02-21-2023, 12:41 AM

Re: LG LCD panel lighter band that goes away

Originally posted by Davi.p

have you got a capacitor meter? the test is fast

I think I will just keep current solution for now. The solution with leaving plugged in for couple of hours is common usage profile, problem never appear again until next unplug for another 2 hours. So I will stop chasing problem now

**howardc64** · 03-19-2023, 02:35 AM

Re: LG 49UJ6500 LCD panel lighter band that goes away

An interesting update. The light band seems to have gone away...

After plugging the TV in for a week and using it (rarely and briefly). Unplugging it for 2x 24 hour cycles didn't result in band appearing at the top anymore.

Interesting result. I guess something takes many hours to fully charge up or discharge haha.

LG 49UJ6500 LCD panel lighter band that goes away

LG 49UJ6500 LCD panel lighter band that goes away

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