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Panasonic TX-32PM11 100hz Quintrix - Extra Pixels?

Discussion in 'Televisions' started by slde, Dec 19, 2004.

  1. slde

    slde
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    Good evening all technologically concerned creatures of the night,

    Just noticed on our TV - exactly halfway up each side of the visible display, there is an extra pixel just outside the boundary lines of the display. Is this something to do with the mask/ie: a standard feature. It is on both sides of the display - symetrically.

    Anyone know why?


    Many Thanks
    Dave C
     
  2. ScootermanRoger

    ScootermanRoger
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    I believe all CRTs have this, so that (in frame collapse mode) the horizontal line scan can be lined up with these marks to both "level" and "vertically centralise" the displayed picture, by adjusting the scan coils when manufactured, and the vertical centering rings or vertical shift potentiometer after the coils are bonded to the tube. (Early tubes had clamps around the tube necks instead of glue)
     
  3. DRGL

    DRGL
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    My Panasonic TV has them but none on Sony ;)
     
  4. Zacabeb

    Zacabeb
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    Many brands add pixels to either side of the CRT, one of the exceptions aside from Sony seems to be LG.Philips.

    The extra pixels can be distracting at first, but they are quite useful when adjusting the geometry of the set, such as vertical linearity and alignment. Without them, the center of the screen has to be marked with tape when adjusting vertical linearity, and that tape will float in front of the image because of the thick glass, giving a less precise reference.
     
  5. slde

    slde
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    just been to the shop and most of the CRTs down there have this feature. Its nice to know its a not a 'fault' as i first thought.
     
  6. GlennP

    GlennP
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    I queried these extra "pixels" myself sometime ago. Toshiba gave me this answer:-

    "The black edge that you get around the TV screen is actually painted on so
    you don't see a jagged edge, it gives the picture a smooth edging. The two
    dots or square "chunks" missing off this are from when the screen was
    resting whilst it was being painted black, this is why you can still see
    the picture behind them. You will find this on most TV's about half way up
    the screen on the left and right hand sides".
     
  7. Zacabeb

    Zacabeb
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    I've heard some tall tales, but that one... :rotfl:

    I hate it when manufacturers, short of actual information, make stories up like that. It might satisfy their need to get things overwith, but misleading consumers with something made up on a whim is poor service on their behalf. I've had many bouts with tech support staff who know less about TV technology than I do. I'm actually surprised they didn't give you the standard "check the aerial" response. :rolleyes:

    The phosphor dots in a CRT are actually layered on the inside of the faceplate by coating the inside with phosphor and a photoresist layer, then temporarily mounting the shadow mask and projecting a light source from a single point behind. This hardens the photoresist, and after that the shadow mask is detached and the rest of the phosphor washed away. This is repeated for each of the threee phosphors.

    The inside of the faceplate is then coated with a layer of graphite to fill the void between the phosphor dots and edge around them with black, and then a layer of aluminum making the screen conductive. After that, the shadow mask is mounted permanently. It's the holes etched in the shadow mask that determines where phosphors will appear. So, those extra dots are there because they were already etched in the shadow mask.

    So, when the graphite is layered, the phosphors are already well in place. The black edge around the screen is in fact not black, but caused by the dark tinted or coated glass not letting light through. If you shine a flashlight into it you can see inside the glass, possibly all the way to the frit seal between the faceplate and funnel of the CRT. On some CRT's, you can even see the shadow mask mounts embedded in the glass of the faceplate in the corners or along the sides of the screen.

    So the dots are fully intentional, both for factory alignment of the CRT and geometry adjustment in the final set. The reason why some manufacturers do without them is because they use different methods for alignment which do not require these extra dots for reference.
     
  8. slde

    slde
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    Zacabeb, do you build CRT's for a living? I am impressed at your build knowledge!

    I reckon the actual tube in my Panasonic 32PM11 has been installed in the housing about 0.5-1mm off horizontal - although I'm not 100% sure whether my eyes are playing tricks on me. I've tried to measure it but it proves difficult because the tube is about 10mm or so behind the glass plate on the front.

    What do you reckon?
     
  9. Zacabeb

    Zacabeb
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    No, I don't build CRT's for a living, but I've spent a lot of time reading about how they are constructed and manufactured since I'm both fascinated and terrified by them. I've learned much of the above from reading stuff at http://www.repairfaq.org . I have also once removed an imploded CRT from a friend's cheap 14" set that kissed the floor and studied it.

    I've seen CRT's shifted to the side and slightly rotated when looking at TV's in stores, although it seems to be quite rare. Maybe with some cabinet designs it's simply difficult to align them precisely when building the set. I would like to imagine there's usually some kind of riser on the mounting posts going into the lugs on the CRT and keeping it in place. I don't know if that's really done.

    It would probably be difficult for a service technician to align the CRT better though.
     

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