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Pincushion?

Discussion in 'Electronic Repair' started by solder lung, Aug 1, 2005.

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  1. solder lung

    solder lung Guest

    My Alphascan 511 Sampo 15" monitor has a weird problem. The pictures on
    the
    link below describes the image problem. This is the farthest that I can
    correct with controls in front. Resetting it to the default factory
    setting just makes the image more unbearable. Brightness, Contrast,
    Colors are good but I just can't seem to straighten the edges! .. and
    so as the image also. Any suggestions? Is this a sign of a leaky cap?
    in what areas should I start looking? Thanks in advance..

    http://img.photobucket.com/albums/v249/celerino/alphascan511/DSC01665.jpg
    http://img.photobucket.com/albums/v249/celerino/alphascan511/DSC01668.jpg
    http://img.photobucket.com/albums/v249/celerino/alphascan511/DSC01670.jpg
    http://img.photobucket.com/albums/v249/celerino/alphascan511/DSC01672.jpg
    http://img.photobucket.com/albums/v249/celerino/alphascan511/DSC01674.jpg

    -mike
     
  2. Franc Zabkar

    Franc Zabkar Guest

    If this is a digital monitor, then I expect that its uP would be
    adjusting the pincushion via an E-W correction IC. If you are
    completely in the dark, then you might consider recording the part
    numbers of the various ICs and searching the Net for their datasheets
    or functional descriptions. ISTR there was a particular ST
    Microelectronics IC (8-pin DIP?) that caused a few E-W problems in
    some monitors.


    - Franc Zabkar
     
  3. solder lung

    solder lung Guest

    There is on made by ST micro.. its a dual op amp LM358n.. i'll try
    replacing this and see how it goes. thanks
     
  4. Franc Zabkar

    Franc Zabkar Guest

    I was expecting something like a TEA2031A, but that was just a WAG.
    The E/W correction can be done in *many* different ways. You really
    need to identify the various ICs. E-W correction works by varying the
    current in the horizontal yoke according to the vertical beam
    position. The current is at maximum when the beam is at the middle of
    the screen, and minimum at the top and bottom of the CRT. What you
    should be looking for is an additional coil or transformer in the
    horizontal section that is driven by a parabolic signal from the
    vertical section. For example, a model 4CM8270 15" Philips monitor has
    an E-W circuit which is controlled from the "Vertical Parabola Output"
    pin (11) of the TDA4850 H&V deflection controller IC.


    - Franc Zabkar
     
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