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Annoying image distortion on CRTs - cause? workaround?

Discussion in 'TVs' started by Colgate7110, Oct 16, 2004.

  1. Colgate7110

    Colgate7110
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    Hi folks,

    This has been bugging me for a while but I've really started to notice it lately - I'm referring to the way the image on a CRT screen distorts depending on what it's displaying, i.e. when a bright area is introduced to a generally dark screen, the dark area seems to bulge outwards away from the light patch.

    I've rarely noticed it watching films or TV broadcasts but it's incredibly obvious when gaming where screens are often composed of very geometric elements such as menu options. I've seen it a handful of times when watching a broadcast with black horizontal bars along the top and bottom and it looks like the bars are wobbling a bit in relation to the onscreen action.

    Less expensive computer monitors often exhibit this problem when the screen fluctuates from dark to light and I understood it to be down to inferior voltage regulation. Can somebody explain what actually causes it?

    I'm noticing it a lot on my Panasonic TX32-PD30C and was wondering if this something that can be fixed with appropriate settings or a service, whether it can't be fixed and my PD30 joins the pile of problem sets, or is it simply a phenomenon of CRT technology and I should just ignore it!

    Out of curiousity, I dropped my brightness and contrast options to the point where the screen was almost blank except for the defining lines making up the party selection screen in Staw Wars: Knights of the Old Republic on Xbox and it still happened then so it doesn't look like it's a user-controllable effect anyway.

    I'm arranging for an engineer to sort out the geometry on my PD30 (it's new enough that I might as well get it done for me) so if this is something that can be rectified then great. I don't remember seeing it before on the PD30 but I've seen it on just about every TV I've ever watched over the years from large Panasonics and Sonys down to portable JVCs and Philips sets.

    Apologies if this has been discussed before - I tried the search a good few times but nothing turned up. Any info most appreciated!

    Cheers,

    Colin
     
  2. probedb

    probedb
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    There was some discussion in a thread about a JVC TV recently.

    It's something to do with voltages etc. I get it on my old Panasonic, only way to get rid of it to a certain extent is to turn down the contrast :(
     
  3. LV426

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    It's symptoms like this that give the lie to the often quoted assertion that "CRT is best". In this, and certain other respects, they simply aren't. There's nothing wrong with your TV, except that it was built down to a price, rather than up to a standard. And, as a consequence, the artefact which, as you say, is down to poor voltage regulation (in other words, a barely adequate, or actually inadequate) power supply.
     
  4. Laurel&Hardy

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    And why is this happening do you think? Because the mass market wants a bloody huge screen for stupid money. So to get the costs down things have to give. To build it properly costs money but, for example, if you're presented with two 32" flat crt's, one costs £500 but the other was £1,500 and the only difference was that the latter has a PSU worthy of a 32" tube which would you buy? In my case I already know the answer - the £1,500 one because I hate nothing more than to see crap EHT regulation. The trouble is that everyone wasnts something for nothing so high end CRT's are now becoming increasingly rare, just as they are in PC's, even though they still have so much to offer. It seems total madness to me that people are willing to splash out thousands of pounds for the flat panels, yet would never consider such a sum for a CRT.

    And I will assert that CRT is best. It isn't geometrically perfect and it has many flaws but overall a good CRT from Panny, Tosh and Sony amongst others tears Plasma and LCD to shreds when it comes down to WATCHING the thing, not admiring the theoretical advantages of contrast ratio and the lack of geometric flaws on test images.
     
  5. Londondecca

    Londondecca
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    Is it therefore possible to upgrade a power supply in a TV as is common practise in the HiFi world (I accept TV's work at very high voltages).
     
  6. Tight Git

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    Well in theory anything's possible, but it's hardly practical.

    Again to keep the cost down, the PSU in a TV is generally integrated into the main circuit board, so any upgrades will be difficult.

    Perhaps the smoothing capacitors could be replaced, if there's room (and if you know what you're doing), but not much else.

    It's all down to market economics...
     
  7. LV426

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    Each to their own, as they say. However,

    - modern trends in broadcasting style with on-screen graphics, news tickers and the like
    - the need to properly display 4x3 material on a 16x9 screen
    - letterboxed widesreen films
    - etc

    mean that it no longer takes a test signal to demonstrate - to the point of annoyance, (I'd say) deficiencies in CRT performance - variably curved edges to that 4x3 image; bouncing logos; tilted or curved edges to letterboxed films and/or text and/or graphics; colour impurities due to a nearby radiator and so on..

    No platform is without its flaws. I'm sure that a theoretical well-made CRT hads the propensity to beat anything else, at present. Regretfully, for the reasons you rightly say, they are hard to come by (or even, don't exist).

    Which is best depends on personal preference - which artefact is least intrusive to whoever is buying. I guess it would be a brave manufacturer, though, who brought out a large CRT costing a similar amount (or more, even) to a flat panel, but with performance fitting of its cost. It probably would be a flat-panel beater - but would enough folk buy one?
     
  8. Laurel&Hardy

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    All but impossible, unless you have intimate knowledge on how these things work. By altering one part of the PSU you may inadvertently overload another, ect, so unless you want smoke instead of pictures the only upgrade is a better built TV, and if you're after a CRT that's going to be hard sadly.
     

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