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Panasonic TX-L50B6B screen "blotches"

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    Panasonic TX-L50B6B screen "blotches"

    This post is more a "what's going on here" thing than anything else but here goes.

    The above Panny 1080P LED back-lit TV is about eight years old now. About three years ago the dark blotch that can be seen in the lower middle of the image appeared, and it has now been joined by its brother to the lower left. I was able to get used to the first blotch but this second one is annoying.

    Both appeared in a similar way. They started off only being dark when the set was first switched on from cold. They'd start off dark, then flicker dark and bright for a while before finally disappearing and staying bright.

    If the set was set to low back light setting (30%), they'd be more prone to staying dark for longer. At full back light they'd go bright.

    This state only lasted a few weeks before they became permanently dark.

    My first thought was dead LEDs but surely these are series-string so if one goes (and certainly two, with one being dark for years) they all go?

    Or is this something else - warping of one of the layers inside maybe? The flickering goes against that theory though.

    Just curious as to what the failure is here and ultimately if it's going to result in eventual total panel failure.

    Any views gratefully received. Ignore the dark horizontal band BTW, that's a camera/PWM artefact in the image.
    Attached Files
    Last edited by jjne; 05-23-2021, 05:15 PM.

    #2
    Re: Panasonic TX-L50B6B screen "blotches"

    That has faulty LEDs (or LED controller/driver) written all over it!
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    "¡Me encanta "Me Encanta o Enlistarlo con Hilary Farr!" -Mí mismo

    "There's nothing more unattractive than a chick smoking a cigarette" -Topcat

    "Today's lesson in pissivity comes in the form of a ziplock baggie full of GPU extension brackets & hardware that for the last ~3 years have been on my bench, always in my way, getting moved around constantly....and yesterday I found myself in need of them....and the bastards are now nowhere to be found! Motherfracker!!" -Topcat

    "did I see a chair fly? I think I did! Time for popcorn!" -ratdude747

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      #3
      Re: Panasonic TX-L50B6B screen "blotches"

      Originally posted by RJARRRPCGP View Post
      That has faulty LEDs (or LED controller/driver) written all over it!
      Thanks - I get that but is it actually possible for LEDs to fail and the rest to stay operational?

      Comment


        #4
        Re: Panasonic TX-L50B6B screen "blotches"

        It is likely that the individual led has shorted allowing the rest of the string to still work, most led driver circuits would normally shut down the backlights but not always.

        Comment


          #5
          Re: Panasonic TX-L50B6B screen "blotches"

          That was my original thought when the first LED went a few years back but I was advised at the time by someone who professed to know what he was talking about that they don't fail in that mode.

          That doesn't matter though, if it is indeed a case of two LEDs failing short then I suspect that the TV isn't far from a failure due to, I assume, higher stress on the remaining LEDs.

          Comment


            #6
            Re: Panasonic TX-L50B6B screen "blotches"

            That tends to be the correct conclusion. Shorted leds place higher strain on the remaining leds.
            Willing to help but I'm no expert.

            Comment


              #7
              Re: Panasonic TX-L50B6B screen "blotches"

              Led failure I have had the set myself with exactly the same issues. I have replaced about 4 led strips since I have had it for about 3years.
              The leds before tend to blink then finally for about a week then die. After about 3 fail the backlight of the screen dies!

              Comment


                #8
                Re: Panasonic TX-L50B6B screen "blotches"

                Also watch out for a symptom that seems to be more common now, blue-and-purple backlight LEDs!

                Especially LCD TVs built in 2016 and around there. But it's possible that the problem is still continuing. Seems likely to "conveniently" occur in only 3 or 4 years of use!
                Last edited by RJARRRPCGP; 05-26-2021, 04:56 PM.
                ASRock B550 PG Velocita

                Ryzen 9 "Vermeer" 5900X

                16 GB AData XPG Spectrix D41

                Sapphire Nitro+ Radeon RX 6750 XT

                eVGA Supernova G3 750W

                Western Digital Black SN850 1TB NVMe SSD

                Alienware AW3423DWF OLED




                "¡Me encanta "Me Encanta o Enlistarlo con Hilary Farr!" -Mí mismo

                "There's nothing more unattractive than a chick smoking a cigarette" -Topcat

                "Today's lesson in pissivity comes in the form of a ziplock baggie full of GPU extension brackets & hardware that for the last ~3 years have been on my bench, always in my way, getting moved around constantly....and yesterday I found myself in need of them....and the bastards are now nowhere to be found! Motherfracker!!" -Topcat

                "did I see a chair fly? I think I did! Time for popcorn!" -ratdude747

                Comment


                  #9
                  Re: Panasonic TX-L50B6B screen "blotches"

                  Originally posted by dick_barton View Post
                  That tends to be the correct conclusion. Shorted leds place higher strain on the remaining leds.
                  Not necessarily.
                  Is same current is maintained, no additional stress.
                  But old LED's are still wearing out like the first ones that failed.

                  Comment


                    #10
                    Re: Panasonic TX-L50B6B screen "blotches"

                    Thanks for the replies. Hopefully the set will last a while longer (I want to upgrade to a 60-65“ but my current house really isn't big enough for that! ) but if not I'll be pulling it apart and replacing LEDs Never done it before so hope I don't bust the screen in the process.
                    Last edited by jjne; 05-27-2021, 05:38 PM.

                    Comment


                      #11
                      Re: Panasonic TX-L50B6B screen "blotches"

                      Originally posted by jjne View Post
                      Never done it before so hope I don't bust the screen in the process.
                      Broken after changing LEDs?=Mea maxima culpa!
                      ASRock B550 PG Velocita

                      Ryzen 9 "Vermeer" 5900X

                      16 GB AData XPG Spectrix D41

                      Sapphire Nitro+ Radeon RX 6750 XT

                      eVGA Supernova G3 750W

                      Western Digital Black SN850 1TB NVMe SSD

                      Alienware AW3423DWF OLED




                      "¡Me encanta "Me Encanta o Enlistarlo con Hilary Farr!" -Mí mismo

                      "There's nothing more unattractive than a chick smoking a cigarette" -Topcat

                      "Today's lesson in pissivity comes in the form of a ziplock baggie full of GPU extension brackets & hardware that for the last ~3 years have been on my bench, always in my way, getting moved around constantly....and yesterday I found myself in need of them....and the bastards are now nowhere to be found! Motherfracker!!" -Topcat

                      "did I see a chair fly? I think I did! Time for popcorn!" -ratdude747

                      Comment


                        #12
                        Re: Panasonic TX-L50B6B screen "blotches"

                        Mind the corners when you refit the LCD, it can pop out of the channel it sits in as you refit the front bezel.

                        Comment


                          #13
                          Re: Panasonic TX-L50B6B screen "blotches"

                          Well yet another LED has failed so I suspect this is happening sooner rather than later.

                          The LEDs are normally £70 a set, which frankly is a lot to pay on an 8 year old TV... But, I've seen that you can get complete sets from China (this is an LG panel, LC500DUE) for a fraction of this (about £20 or so). Are these cheaper kits any good (I imagine the more expensive ones aren't original LG!) or do I avoid?

                          Comment


                            #14
                            Re: Panasonic TX-L50B6B screen "blotches"

                            My thoughts would be buy the china set replace them and then sell the TV. I haven't rated the Panasonic TV myself as I had the smart version of the same set. The apps gradually stopped working as did the leds. Replaced around 4 or 5 strips on this set in the lifetime I had it. Pretty much all the apps failed on the TV.
                            So personally speaking don't buy a smart TV just get an amazon dongle or equivalent device to get updates that the TV manufactures rarely support after 3 years of production. They have no interest in providing updates just wish you to buy a new one! So get a decent non smart TV and save yourself money and grief long term by getting an HDMI dongle which amazon will support as they have millions of devices that they wish you to use with there services.

                            Comment


                              #15
                              Re: Panasonic TX-L50B6B screen "blotches"

                              Luckily, it looks like this model uses the same strips as LG 50LN series which are a common failure. Otherwise, Panasonic parts can be impossible to find. I have used new substitute strips from Chinese sellers on both ebay and Aliexpress for this model with no repeat failures. Just turn down the backlight after and do it for all inputs and all apps.
                              Last edited by neilc6; 06-09-2021, 03:25 PM.

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