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Toshiba vertical problem

Discussion in 'Electronic Repair' started by David Wolff, Jul 18, 2003.

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  1. David Wolff

    David Wolff Guest

    Repaired a Toshiba t.v. with a vertical problem caused by bad
    capacitors. After fix, vertical is short on top and bottom equally.
    Attributing this to set needing adjustment upon new components. Size
    can be properly adjusted with vert height adjust. Problem now is that
    vertical size flucuates a bit depending upon brightness of scene being
    displayed. It isn't very noticeable, but I am wondering if it is
    normal operation or if there is some other problem. Maybe it's just
    the way it's designed because I see no regulation of the vert out
    supply. Seems like if there is a problem it would be with voltage
    regulation, but vert out supplies seem reasonably stable (a bit of
    variation, maybe .2 V). It's not vert supply filter capacitors,
    ripple remains constant. I don't have a schematic, but the supply to
    vert out comes from flyback so if vert supply is varying, then B+ must
    be varying too much? Customer saw the set and didn't notice the
    problem, am I just being too critical?
  2. Sofie

    Sofie Guest

    David Wolff:
    With a variac do a basic main power supply B+ regulation check to verify
    that it holds regulation when the AC Line input is varied from about 105 to
    120 V. You also may want to check and/or replace the filtering
    electrolytics in the main B+ supply...... and also check the flyback derived
    B+ electrolytics. Also you could be seeing the result of screen supply
    regulation problems, particularly if the picture size changes when the
    average brightness level changes..... around the flyback look for low uf /
    high voltage electrolytics...... i.e. 10uf @250 v .... or similar.
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