LG 55UN7000PUA fixed with just dis/reassembly

[howardc64]

TV runs, backlight on, have sound and no image (dark grey/blue/black LCD)

Disconnected right (looking from rear of TV) tcon-buffer board cable, LCD left half displays.
No shorts on right buffer board.
Started masking tcon-buffer board signals... (connection #1 in main board pic) about 20+ pins from top of connector... LCD fully displays with some anomalies.
Gradually reduced # of masking signals... eventually down to 1. Removed that... LCD works perfectly.
No obvious damage on right buffer board 3x COF to the panel like another 43" LG fixed ( link ) with similar poor design ( COF/flex rubs against the metal buffer board guard )

Masked the metal buffer board guard with electrical tape ( orange color in pic ) Will observe for a few days. My best guess is some micro short was occurring from COF to the metal guard.

[nomoresonys]

Nice, looks like something else folks have to watch out for, you are the man.

[howardc64]

Nice, looks like something else folks have to watch out for, you are the man.

Yes, any of these ~2020 era LGs probably should have the metal buffer board guard electrically masked whenever opened. This one has ~4k-5k hours on it. Don't recall the how many hours prior repaired 43" had.

[Howard_Woodard]

That's it? Just 6 little pieces of orange masking tape? Goot job maun.

[howardc64]

One thing that might be of interest is the center of COF (Chip On Flex) has a bright copper diagonal line (~1-2mm) facing the metal guards. Was on all 6 flex COFs between buffer board and panel so its by design. Didn't do continuity test. Unfortunately wouldn't show in pic but I've drawn it in for reference.

Curious what this is for. Can't be for ground as COF can get much more solid ground via flex -> buffer board -> main. If this copper color diagonal is connected to a useful trace, then having it rub and face directly to the metal guard seems undesirable. Perhaps the flex thickness offers a gap but it is a tiny gap.