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A couple of days ago, I was walking past my tv set (which uses an old-fashioned crt) and I saw an illuminated triangular shape on the screen, about the lenth ...
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  1. #1
    Linux Engineer hazel's Avatar
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    Strange behaviour of a television set


    A couple of days ago, I was walking past my tv set (which uses an old-fashioned crt) and I saw an illuminated triangular shape on the screen, about the lenth of a finger joint. It was made up of vertical lines in a vivid fluorescent green. The set was switched off at the wall, not on standby.

    I unplugged the set, but the shape remained in place. I plugged it in again and switched it on. It displayed a normal picture. When I switched it off again, the shape was gone. I have not seen it again.

    I know that crt screens contain coloured phosphors that react to the electron beam but what could have caused this long-term phosphorescence? Is my set haunted?
    "I'm just a little old lady; don't try to dazzle me with jargon!"
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  2. #2
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    Old CRT sets build up funky magnetic fields over time. Sometimes they will go away after power cycling / internal degaussing circuit, other times you need to degauss your set with a degaussing wand.

    Degaussing a CRT manually - YouTube

  3. #3
    Super Moderator Roxoff's Avatar
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    Those heavy glass tubes take a huge voltage to make them work, and they end up storing a huge potential difference for ages after the power is cut. They can slowly discharge, but as they get old, it's no real surprise that they can leak that power out into the tube itself.

    I'd take it as a sign that the tube is starting to fail. Perhaps it's getting close to the time it needs replacing. A modern LED flat screen telly will use considerably less power, so it'll be more economical in the long run anyway.
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  4. #4
    Linux Enthusiast cousinlucky's Avatar
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    My first thoughts were " ghosts in the machine " and " big brother is watching you "!! ( smiles )
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