Inside LG 4K TV, and My (Unsuccessful) Attempt at Repairing It

Long time readers of this blog may remember that I organized a crowdfunding event aiming at raising funds to buy equipment to test 4K TV boxes and mini PCs in early 2015, and one of the items I ended up purchasing was LG 42UB820T 4K television. It worked well for over a year, but I started to notice a single vertical appear on the TV in June, or about 18 months after purchase.

LG_Television_Vertical_LineA few more lines appeared in the following week, and it appears to have stabilized as shown in the picture below.

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While I understand that in Europe a 2-year warranty period is legally required, I’m based in Asia, and all I got was a one year warranty for the TV. So I had three choices:

  1. Ignore the problem
  2. Pay for the repairs
  3. Try to repair it myself

So far, I’ve selected solution 1. because that’s the easiest one, and the lines don’t matter than much since I only use that TV for reviews. So the only real downside is that I have some vertical in pictures and videos… But today, I had some spare time, and decided to open the TV, and check out the cables as some people on Google+ mentioned it could be the issue. Sorry that I haven’t tested, and have no plans to test, the baseball bat method… 🙂

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Warning: TV have high voltage and large capacitor, so wait a few minutes if you ever intend to open yours…

So I found some towel to protect the panel, and took out the back cover. It’s pretty easy, but you have to loosen all screws on the back, as well as four screws on the bottom.

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Click to Enlarge

There are six main “blocks”: the orange power supply board, the display board in the middle, and what I’d call the mainboard or input board on the right, as well as two dual speakers, and the IR bracket in the bottom center.

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The power supply board is fairly large, takes 100 to 240 V @ 50/60Hz AC input, and outputs four DC voltage levels: 3.5V @ 1.0A, 12V @ 3.0A, 24V @ 1.0A, and 50.4V @ 0.95A.

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The display board (V14 TM120 UHD ver0.6) features LG Display TLi2450MC LCD driver, and is connected to the main board via one flat cable, and the the LCD panel boards via two ribbon cables.

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The “input” board has all video input ports (HDMI, AV, component), Ethernet, the DVB-T2 tunner, USB ports, and most ICs are covered by heatsinks, which I have not messed with.

I disconnected the ribbon cables connected to the display board, checked for dust, and reconnected them. But since i thought there was certainly more than I could do, I did some research, and found one video explaining one possible cause for the vertical lines.

The problem in the video above is clearly with issue related to the ribbon cables directly connected to the top of the LCD panel, and pressing on the cable may remove the lines. Sadly the video did not offer a solution for the problem, only demonstrated the reason.

Still I wanted to check it, and put back the TV on its two feet…
… and found out a metal bar on the top just like in the video above.
But sadly, there wasn’t any ribbon cable in that location. But I still connected the power to check if I could impact the display with some non-conductive tool. No luck.


Nothing to see here, so I re-assembled the top of the TV, and when looking on the bottom instead.
I could see a black bar with two screws on each side, and I loosen two more screws to remove the IR bracket, and found two extra screws.
Taking those out, allowed me to discover the ribbon cables I was looking for.

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Click to Enlarge

But since I did not have full access just yet, I took out the speakers, which are very easy to remove since there aren’t any screws or other mechanism.

Now it’s easy to understand that the two white ribbon cables connected to the display port are connected to two “zones” connected to the LCD panel. I have problem with lines on the right part (from this angle), so I loosen a few more screws, and I could get a clear look at the board and ribbon cables connected directly to the LCD panel.

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Click to Enlarge
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The board is called B1 42UHD RIGHT Ver 0.5, but I could not find obvious fault with any of the ribbon cables, and it’s unclear how they are connected to the board. Since they are placed at the bottom it’s also not really convenient to connect the power and check out what happens when pressing the cables, so I gave up. Nevertheless, it was an interesting exercise!

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23 Replies to “Inside LG 4K TV, and My (Unsuccessful) Attempt at Repairing It”

  1. What about the other way around: if you *remove* a flat cable, do a lot of lines turn black?

    If so, you can confirm your hypothesis, and find the correct flat cable.

  2. i wish you luck to repair your tv as your reviews of all devices are very good and personally very important to me when taking decision what to buy for myself and friends

  3. pre 2010 LCD with lines was usually the ribbon, glass itself had healthy margins, post ~2010 manufacturers streamlined processes to the point they could finally optimize(*) for the price aka cut corners = defects are inside the glass, no amount of poking will help. Buy TV with extended warranty, or really cheap models that wont sting when dead after <2 years.

    * also planned obsolescence

  4. This is definitely a tab bond issue. Most of these LED TVs should not be run on high contrast to reduce heat. It was a big problem on CCFL backlight panels.

  5. @Sander
    I could remove the ribbon cable to check it out, but I have no idea how to put it back… There’s no connector, the cables appear to be taped to the board…

    Thanks. The TV is still working, and just a few vertical lines won’t stop me from reviewing TV boxes or mini PCs.

  6. Suggestion.

    You review hardware although mainly non TV but a TV is required for many of your reviews. So class this as a review of LG TV , contact LG support and direct to you LG TV reviews and problems. Who knows they may or may not care about their products public image.

    Have you asked around for repair costs?

    Here in UK my HD TV 46″ LCD was never new I bought it off eBay, manufacturer’s returns, in 2012. Have you checked what your TV might be worth second hand? Or how much a secondhand one is?

    Just some thoughts.

  7. @theguyuk
    I don’t know about the repair costs, but they told the “check your TV” costs are at least $30.
    I can still use the TV as it is, if it gets worse, I’ll see what my options are.
    If the panel needs to be replaced I’d assume it will be expensive, in that case I might consider buying a different 4K TVs with 3D and HDR support for example, depending on the price at the time.

  8. @cnxsoft
    the data ribbons fault usually happens on the panel side (which heats up) not on the track/signal spliter board accessible from the back.

    A very quick and easy way to troubleshoot that is to use a “freeze” spray, a simple dust spray should also work if you’re generous enough, and while the tv is on, spray along the side where you’ve located the data ribbons.
    It’s usually on the top or bottom side, here on the bottom if i’ve looked at your pictures correctly.

    So you would pray along the bottom side facing the tv around the area where the lines are located, if it’s not doing anything try to spray the lateral or top side too, until you see something.

    here’s a demonstration of that process :

    In any case, if it fixes the problem it means you have a faulty panel which can be fixed but it’s not an easy task and not one you can perform without specific soldering tools.
    And the panel assembly is usually a pain and can come apart with not way to put it back properly.

    As stated above it’s really a matter of manufacturing process where they decide not to take into account minimal fault tolerance when the device is operating in a certain temperature range.

    And let me take a wild guess, do you live in an area with hot temperatures (frequently above 35°c) and/or high humidity ?
    (air humidity does not accelerate degradation, although it can oxidize more rapidly but not in a “2 years” range, but prevents proper air convection rates, rendering narrow air vents useless).

  9. @mdel
    The freeze spray is a fun debugging technique 🙂

    The symptoms in the video were quite different from mine though, but I understand the cause may be identical.

    Yes, I stay in hot (35 to 40 C is common) and humid location, but the television is in an air-conditioned room where the temperature is set to 28 C.

  10. In the old days of analog TV ™ freeze spray and heater guns are used to find cold solder joints.

    And for the 2 year warranty period in here in germany this is more complicated.

  11. I’ve just been thinking than one of the silver linings of the vertical lines is that it may help me going through YouTube “anti-piracy filters / algorithms” more easily when doing reviews. Normally if you play a movie or video which happens to be copyrighted for even just 20 to 30 seconds they’ll cause some issues.

  12. @cnxsoft
    3M has a double sided conductive “duck tape” which has conductive columns inside. These kind of connections (PCB 2 flex) were used to be repaired this way. Anyway I am not 100%ls sure that those connections are the root cause of the fault. Ask someone to check the display why you are touching/pushing those connections to locate the problem. These kind of issues used to be caused by defective TCON board which is on your 6th picture.

  13. I doubt this is the problem but it’s worth a shot. I’m guessing you’re swapping hdmi cables in and out during testing. Try using some canned air and blowing out the HDMI slot you’re using. 99% chance it won’t help but 30 seconds might save you a lot of time and money.

  14. Agree with several of the other posts here, sounds like a tab bonding issue on the flex ribbon cables going into the display (brown cables in the last 3 photos). Sometimes, like stated in the video you linked to, it’s the bonding compound attaching these cables to the circuit board that wears out, but more often it’s the IC embedded inside each of the ribbon cables themselves that starts to lose its bond causing vertical lines on the screen. The recommended fix I saw on was to put a thermal insulator pad on top of where the IC chip is in the cable and the TV case so the chip is squeezed against the cable when the TV case is reattached.

    See this video for an example:

    If it’s a tab bonding issue, I would recommend putting pads on all the display ribbon cables because once one cable starts to lose it’s bond, it’s not uncommon for other cables to start losing their bond later on. If you have to remove the connector from the T-Con board, be careful when reattaching them, it’s not hard to damage the cable when reconnecting it if everything isn’t lined up just right.

  15. In the UK, we don’t have ‘2 years’, instead we have the normal ‘1 year’ plus a law that means if something fails earlier than you’d reasonably expect it to, then it should be repaired (Sale of Goods Act) This can be tricky to use – so I always buy my TVs from ‘John Lewis’ who are usually very good value, and include a 5 year guarantee for TVs at no extra cost.

  16. I ended up with the same problem on a ThinkPad x60 LCD. But I was touching the tab bonds unknowingly while handling the screen so I thought I managed to break a few lines in one.

    I was waiting for a thin voltmeter and a microscope to tap into each lines trying to find a broken link. Good luck.

  17. I’m facing HDMI no signal issue for this LG 42UB820T 4K model. That LG Service Man said TV motherboard need to change. Any suggestion please.

    1. It’s pretty hard to fix a TV oneself. So if the price is OK, I’d recommend going with LG service man recommendation.

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