Chosen Solution
So I noticed that my screen was flickering last night (and it seemed to be fine today, until now) , however it doesn’t seem to be like the flickering seen in other videos showing screen flicker where the screen goes off and on like a broken fluorescent light (which seems to happen to TVs using LED backlighting like mine) instead the best way to describe it would be like a rapid pulsating where the screen dips in brightness and increases in cycles, it’ll ‘pulsate’ maybe 20 times over a two second period then be normal for a second then repeat the process over again, the entire screen is still visible during this, at no point does the screen go black entirely (at least not for a duration visible to the human eye, I’ll record it in slow motion and see if there’s more than the usual 60hz flicker) this flickering is intermittent and at times the TV seems totally fine, except for a very thin (invisible at even 1.5m/6ft distance) horizontal bar near the very top of the screen which is more visible on the right hand side and flickers at the same rhythm as the entire screen. The fact that there’s a thin bar makes me think that there may be an issue with whatever is driving the display rather than a ‘simple’ LED issue. There is a slight hum from the TV too (from the SMPS I assume) , however I’m not certain if that was always there and I’m just noticing it now. If anyone has any idea what this might be just from the description alone that would be great. However if that’s not the case I can open it up and check the boards for bulged/leaking capacitors and any components which have maybe burned up/otherwise gone bad. I own a multimeter (though nothing exceptional like a fluke) and have a bench PSU and soldering station so I can desolder and check suspect components and hopefully replace them. I really don’t want to buy a new TV (and if I do it won’t be LG, I’ve owned this for just over 3 years and babied it, turning it off even when I leave the room for ten minutes (mainly for electric bill reasons) on the other hand my mother’s Samsung gets left on overnight with no auto off feature and has been owned for about 12-15 years and its still great) so any help would be really, really appreciated. Thanks Updates and images below: Update 26/05/20 Although a T-con board is being sold for this model number of TV in on ebay it must be mislabelled as the two LVDS cables on my TV go straight to the scan drive boards. So I think (confirmation would be great) the T-con board may be integrated into the motherboard on my TV, I’ve stripped the TV down as far as I can go without taking off the panel itself. I have close up images of the scan drive boards too however they looked to be in good condition (and I assume that if they fail its game over anyway) any idea on how I should proceed now? The flickering seems to be happening more and more often (less than half an hour of running my TV tonight however it always starts up fine) should I just run it until it lets the smoke out and find out what failed? Or should I replace the main board which is also the T-con board as the boards which connect directly to the panel are completely fine. Obviously I’m not looking for an answer that is a definitive fix (as I can’t find a definitive problem) and I’m not the type of person to pull a “well you said x and it didn’t work” when it comes to free advice, so if you can give me your best reckoning based on prior experience that would be great. Final update: I opened the TV up a fourth time as I needed the part number on the mainboard and removed the main board entirely to check underneath to see if there were any scorch marks there. There was nothing. I then replaced the motherboard and plugged all the cables back in then ran the TV for a while to see if some of the power inductors were getting too hot (they looked slightly toasty but not burned up) but they seemed fine, I felt the heat on the main IC heatsink and pushed down on said heatsink a little too. I reassembled the TV and the flicker (including the single flickering horizontal line) has gone (or at least it hasn’t started up again) so maybe it was an LVDS cable issue (previously I lifted the flaps and gently pushed them in to make sure they were seated correctly but didn’t remove them and plug them back in) so maybe this removed the flicker, or maybe it was me pushing down on the heatsink. Or maybe it somehow resolved itself (though I doubt this). However I have horizontal bars (multiple) running across the screen mainly on the top right hand side. They’re barely visible unless I get to about 3 feet from the TV and they seem to have showed up with the flicker as they weren’t there a week ago when I took a picture of my screen to remember a location in RimWorld (a video game) and they weren’t there in that photo I’ll make another thread on this as they don’t fit the thread title or subject. I’m not 100% sure what fixed this but since I unplugged all cables going to my TV motherboard and reseated them I’ll give the answer to @oldturkey03 thanks for all your help! Image links: Power distribution board Lower quality: https://ibb.co/42c3ycQ
High quality:
Logic and image board Lower quality: https://ibb.co/R4SZ5DF
High quality:
Top down:
Side on:
The horizontal line with a ruler for scale https://ibb.co/XZ01XFS
Took new images with a DSLR, they are of significantly higher quality, they also show all the PCBs that I could find (except for the button and radio board) note that the speakers were removed for the side on and top down shots as I needed to remove some metal shielding covering the two PCBs that the LVDS cables connect to. I also have the images linked below. Got a video of it (embedded on website linked below, so no need to download a potentially malicious file) the camera on my phone is producing patterns which look like moire lines which aren’t visible to the naked eye, only the flashing horizontal line is so they may be the product of recording a screen. Video link below: https://gofile.io/d/BgFc49 Here’s a video of the whole screen blinking. Recording it with my phone doesn’t do a perfect recreation of what I see, for me it seems to flicker more but in a much ‘softer’ manner while the phone only catches the worst of it, however its better than explanation by text and images alone. Video link below: https://gofile.io/d/W9Xhwt I got another 2 videos of it at its worst. https://gofile.io/d/ssg24L And https://gofile.io/d/uLqclK A slow motion (240fps) video of the problem. Not sure if it’ll help, but I’m using every tool I have. https://gofile.io/d/iPQDxb A video after leaving the TV on for about an hour with the problem set to the test screen. It seems to now just change in overall in a slower pattern. Not the quick, seizure inducing flicker it was doing before. https://gofile.io/d/glTDMs A huge thanks to people who have offered help and advice thus far. It is really appreciated. Hopefully I can just source and replace some parts and not have to buy a new TV. Disassembly advice below, related to my problem, just for anyone with the same model (or similar) who needs to get the back off without breaking anything. For anyone looking to disassemble an LG 4k (UHD) LCD TV like 49UH668V (just wording it that way for google’s webcrawler to pick up on it as I couldn’t find any info) the back cover is held in place with a series of plastic clips. I got the first ones going by pushing down on the metal frame where a screw was with a screwdriver and pulled up on that side to pop the first clip out, did the same on the opposite side then used a plastic card to unclip it all after getting it started. There’s also a screw hiding in plain sight amongst the input terminals, but no screws hidden under labels. High quality image links: https://ibb.co/Nt83ygL https://ibb.co/6rBf4yg https://ibb.co/H203d44 https://ibb.co/93pPDdh (old edit) I opened it up and had a look inside, took a few pictures for you too and for the next guy who has a problem with this TV or a similar one so they know what to expect. Nothing obvious jumped out at me, however (what I assume to be the processor on the image/logic board) is making a faint buzz. The transformer on the power distribution board is too, however a 50hz hum from a transformer is fairly normal an IC on the other hand I’ve wouldn’t expect to hear a buzzing sound from, though feel free to correct me if I’m wrong.
@david1892 what concerns me on this is the horizontal line. Normally I would have said the issue here is the T-con board or the main board but neither would leave a horizontal line. Horizontal lines are almost exclusively caused by bad source drivers on the LED driver board. That is the small board which connects directly to the LCD panel. Follow the cables from the T-cob board since those terminate in the LCD driver board. Take a look around that area for components that may look scorched etc. Right now that board would be my number one suspect. Of course check all the other boards as well as the LVDS cables etc. Remove all of them and reseat them, checking the ends for any damage. Post some good pictures of your boards etc. with your question so that we can see what you see. Adding images to an existing question
