Announcement

Collapse
No announcement yet.

"Shadows" on LCD screen. Mura effect?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    "Shadows" on LCD screen. Mura effect?

    I´m asking you for any help about a problem affecting both my NEC SpectraView 2490 and my NEC MultiSync 2490WUXi² LCD monitors.

    Description of the problem:

    After a year - year and a half of use, both displays began to show irregularly shaped dark "shadows" on the right edge from top to bottom of the screen. At first they are not much annoying because they don't affect the main working area, so I tend not to care much about it; also somewhat reassured as I can see that they change over time and don't seem to be a permanent electronic nor mechanical problem (and maybe hoping they will disappear as they have appeared)
    In the next year they have evolved slowly, but lately the change pace has increased, and they are getting wider and "moved" towards the center of the screen affecting the main working area and leaving the displays marginally useful for my professional image editing work.

    Other characteristics of the issue are:
    - As said, the problem seems to be the same, affecting the same area of the screen and appearing between an interval of few months in both monitors (first the LCD2490WUXi2, who seem to ever "lead" in the process, then the SpectraView 2490).
    - The "shadows" are near invisible at the moment of turning on the sets, with a very subtle opposite effect: a clear (light not dark) "cloud" (barely noticeable against the blue uniform background of the start up of the system) the same shape as the "shadows" that appear after 10-15 mins of warm-up, and stay so mostly unchanged for the rest of each session.
    - The "shadows" change slowly over time, "moving" towards the center of the screen as a wave in a beach, with different relative "speed" of the "leading edge", diffusing themselves and leaving relatively clear areas previously covered by them.

    In the attached images you can see the problem in photos taken one and a half month ago, and the evolution to their present state.

    Other info maybe relevant:

    - Both have been bought on Nov 2009 and have now roughly 23.000 hrs of operation. The problem began to show at 9.000-10.000 hrs.
    - They are connected to the same Mac Pro workstation and placed side by side, sharing the same working conditions.
    - They have ever operated following the recommendations in the User Manual, specifically the ones about environment conditions of temperature and moist, cleaning, low brightness level settings, periodic calibration, exposure to sunlight or magnetic fields, etc
    - It seems no other part or subsystem of them have any type of malfunction (abnormal heating, noise, defects in pixels, deformation of images nor colors, etc)
    - The "shadows" seems to be not affected by short time pressure or temperature change applied to the front of the panel (I tried to gently press with my finger and apply some cold directly over them with no results)
    - Off course they are not dirt in the surface of the panel as I tried to remove them by carefully cleaning the displays in many occasions.

    My guess

    As I said, due to the wavy shape, "evolving" nature of the "shadows" and lack of other problems with the sets, I doubt it's a electric-electronic issue (bad PCBs, ICs, caps, connectors, power, etc) or mechanical issue (excessive press in screws, edges or in the middle of display, cracks, bends, etc).
    It is a form of non-uniform brightness issue, seemingly produced by local interference with the backlight. But due to... what?

    So I searched a little on the web and found some references to a weird "mura" effect that (at least apparently) resembles my problem. More or less it can be checked in the webpages:
    http://www.avsforum.com/t/1467644/lc...nce-what-to-do
    http://www.behardware.com/articles/5...ad-pixels.html

    Based on the above, It seems to me that it can be:
    - Very thin dirt between the different back layers of the panel (the least probable to me)
    - Some form of ionization of the LCD TFT panel (following what the Beharware site says about the "type II mura" they describe). Intriguing, but too technical for me.
    - Thermic induced deformation of the diffuser or polarizing layers or their in-between interface (glue?), causing refractive interlayer problems or semi transparency due to slight changes in polarization orientation (most probable to me)

    So, please, help me with

    - Anyone knows that problem?. Which is their nature and the cause of it?
    - There are any solution or improvement possible? Which ones exactly?
    - Can myself perform any action to alleviate or fix the issue?
    - It's a problem plaguing the whole LCD technology, the NEC brand, or just I have had bad luck with my monitors?


    Thank you very much in advance
    Attached Files

    #2
    Re: "Shadows" on LCD screen. Mura effect?

    Looks like probably interior staining caused by moisture build up in that area
    Since this is a ccfl lighted screen, the bulbs tend to be the hottest on this end
    There is a chance it can be wiped out of there with good microfiber cloths and with just a touch of distilled water

    You could try lifting the lcd glass and that will tell you if it is on the glass or in the films
    It is a bit tricky to do and you have to be careful around the lcd ribbons

    you would have to obviously open the screen, then remove the metal trim around the lcd panel (this is usually clipped on and may have some tape and possibly a few screws)
    you might be able to do it with the boards in place depending on how they are mounted ?
    if you have to remove the boards, you'll have to connect them back up after the trim is off so that you can turn it on to see what you are going
    wear rubber gloves, to stop finger oils from transferring to the films and glass bottom. Then you'll have to gently lift the glass up from the bottom edge while maintaining forward pull on the panel so it does not slide backwards towards the ribbons. A suction cup may help get it started. Once it is cracked loose, then turn it on and lift it and see if the discoloration goes up with the glass or stays down below in the films.
    AGAIN, you will be hinging on the top ribbons, so take it easy and slow

    Once figured out you can reach in and try a dry wipe with minimal pressure and see if anything comes off.
    If you try and get stuck or are not sure of something, send a message.

    Comment


      #3
      Re: "Shadows" on LCD screen. Mura effect?

      Many thanks Bammbammfran for your answer.

      So you think it can be some very thin dirt adhered to the internal faces of plastic layers or LCD glass by evaporation of moist...
      Well, it's close to one of my guess, but it was the least probable to me mainly due to the changes in the shape and density overtime of the "shadows", the fact that they don't show until the monitors have reached a certain level of warm up after turn them on, and that strangely some areas affected in the past are relatively clear now.
      To me, if there is some form of fixed dirt it will be visible from the beginning after turning on the sets and be always dark (not very slightly light which is the case). On the other hand, in that case, the changes/evolution expected will have been a increase in size/opacity and, as you can see in the images posted, the actual "shadows" diffuse themselves and leave clear areas previously darkened. Don't you think so?
      Moreover, as I live in Madrid (Spain) a very dry place, at first, it seems to me unlikely it can be related to moisture nor condensation.

      But anyway I will follow your advice and try to open the monitors and check for any stain.
      In the procedure you described its not clear to me what's the position of the monitor you reference when say "to gently lift the glass up from the bottom edge while maintaining forward pull on the panel so it does not slide backwards towards the ribbons" Laying flat over a surface? Front face up or down?

      Thanks again

      Comment


        #4
        Re: "Shadows" on LCD screen. Mura effect?

        it's a panel problem, i'v seen it before.
        if you can fix it is anybody's guess.

        you have a sheet of glass with a polarizer on each side,
        that's your actual "panel"
        behind that are a number of semi-reflective sheets of plastic to act as a defuser and then a thick sheet of acrylic with a white backing.

        now it *may* be between the layers of defuser, but you need to be very carefull if you strip it.
        there are 2 problems.
        first, the panel has a load of flat cables bonded to it that go to a circuitboard on the back - dont twist or pull on them.
        you can read up on these by searching "tab bond"

        second problem to watch for is getting dust between the layers.

        Comment


          #5
          Re: "Shadows" on LCD screen. Mura effect?

          if you can wait a day or two
          I will do a video and post it to youtube
          I have a video of an apple led but that is a different animal

          Comment


            #6
            Re: "Shadows" on LCD screen. Mura effect?

            Originally posted by bammbammfran View Post
            if you can wait a day or two
            I will do a video and post it to youtube
            I have a video of an apple led but that is a different animal
            Thanks. I have waited too much until today... No problem to wait a little more.

            If, as you all suggest, this problem is related to the LCD panel or the diffuser/polarizing back layers, your video will be very useful to show how to deal with them (after reach them, which I can imagine will be different with an Apple LED)

            Comment


              #7
              Re: "Shadows" on LCD screen. Mura effect?

              I am not the greatest camera man !!
              But this may help you
              http://youtu.be/vI1tuQ_3FG0

              Comment

              Working...
              X