My JVC has a burn spot? Please help.

Discussion in 'Archived Threads 2001-2004' started by Mark Roger, Jan 17, 2002.

  1. Mark Roger

    Mark Roger Agent

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    I have a 32" JVC 32020 and when watching a movie that has a white section (sky for example) for more than a few secs. there is a yellowish burn spot that develops on the screen then goes away. Does anyone know what this is called or how to fix it? Thanks in advance.
     
  2. Allan Jayne

    Allan Jayne Cinematographer

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    1. The blue electron beam is unable to maintain high intensity for prolonged periods of time, for a white area, if the blue beam weakens, the color turns yellowish. It could be that the tube cathode (one for each color's beam and responsible for emitting the electrons) can't deliver enough or there is a problem in some of the supporting circuitry outside the picture tube.
    2. On bright parts of the picture, the shadow mask in the picture tube heats up because more electrons from the beam are hitting it. There may be a slight warpage causing misalignment. THis is a "purity" problem, not a convergence problem.
    Try lowering the contrast. This reduces the maximum strength (or strength required) of the electron beams, reduces the shadow mask heating, and also forestalls burning of the phosphors themselves. Many sets come from the factory with the contrast set way too high.
    A tube rejuvenator is sometimes used to fix cathode problems. It does this by giving the tube filaments (that heat the cathodes to cause electrons to be emitted) an overvoltage jolt to burn off dead material on the cathode surface and there is a slight chance of burning out the filaments, killing the tube instantly.
    Other than what I mentioned above, I do not think there is a fix. Shadow mask warpage is a picture tube problem that probably affects your set only but I won't rule out affecting any set using that model tube.
    More video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  3. Mark Roger

    Mark Roger Agent

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    Thanks I'll try your suggestions.
     

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