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Purity problem in Panasonic TV

Discussion in 'Electronic Repair' started by Jeroni Paul, Feb 26, 2007.

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  1. Jeroni Paul

    Jeroni Paul Guest

    Hello
    I've got a Panasonic TV model TX-29AS10F chasis EURO-4H with a color
    purity problem at both sides of top of the picture. Top left has a
    greenish tint and top right is yellowish, the rest is correct
    including top middle. That discoloration gets worse as nearer to the
    edge. This model is 100Hz and has a completely flat CRT front.

    In the user settings it has a geomagnetic correction menu that lets
    the user rotate the picture slightly, the curious thing is that
    adjusting that also moves that purity defect. The right one can be
    eliminated completely this way but then the left one expands even
    more. The opposite is also true but the left one can't be corrected
    completely.

    I wonder if you belive it is more probably a CRT mask defect, a moved
    or misaligned yoke or some missing/fallen magnets. I don't see
    anything wrong apparently in the yoke but before I start playing with
    small magnets around the tube or moving the yoke I ask for previous
    experiences.

    Thank you.
     
  2. hr(bob)

    hr(bob) Guest

    Is the degaussing circuit working. IF you are not sure, get hold of a
    degausssing coil and manually degauss the CRT. You don't say if this
    is a new problem or was that waay from the beginning, and what might
    have happened such as dropping the set, or unplugging a vacuum cleaner
    right next to the set, or whatever. These are im[portant clues.

    H. R. (Bob) Hofmann
     
  3. Jeroni Paul

    Jeroni Paul Guest

    hr(bob) :
    Thank you for replying.
    It appears to be working according to the noise it makes at startup.
    I know, but unfortunately I don't have this info since it came from
    the scrap. A good starting point is that there was some evidence that
    it was neven been opened.
     
  4. Jeroni Paul

    Jeroni Paul Guest

    hr(bob) :
    Thank you for replying.
    It appears to be working according to the noise it makes at startup.
    I know, but unfortunately I don't have this info since it came from
    the scrap. A good starting point is that there was some evidence that
    it's neven been opened.
     
  5. Jeroni Paul

    Jeroni Paul Guest

    hr(bob) :
    I have checked the degaussing coils operate correctly as playing with
    magnets I've magnetized the CRT and a cold degauss restored it. They
    also make a very audible noise.

    Have been playing with some magnets around the tube and found that
    placing a small magnet at the right orientation around the deflection
    coils next to the tube gets rid of the purity problem. Two magnets,
    one per discoloration, I can get it perfect.

    However I wonder if that is the solution to the problem or should I
    look elsewhere for something misaligned. The yoke appears firmly
    attached to the tube without signs of having moved, it is glued there.
    The convergence / purity rings are intact with their original painting
    as well as some adjustment screws around the coils.

    I have noticed there are three windings electronically controlled,
    probably used for rotation. One next to the convergence / purity
    rings, one around the deflection coils next to the tube and one around
    the entire tube together with degaussing coils. What do these do?
    Could a failure of one of these cause the problem (I mean the
    electronics that control them)?
     
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