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vertical overscan in Zeneth color TV

Discussion in 'Electronic Repair' started by [email protected], Apr 19, 2007.

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  1. Guest

    My principle TV has worked ok for years, but has gradually developed
    vertical overscan, especially at the bottom of the screen. (Weather
    scrawls, etc are almost off the screen). I see no vertical height or
    linearity controls brought out to the outside of the case as on older
    TV's. It is a Zenith model SS1915W, but this model is not listed in
    the SAMS index to get a Photofact. Is it simular to one that is
    listed, or anyone have an idea how to adjust this. I know that it has
    an IC to develop the various signals, I replaced that several years
    ago, but don't remember its number.
     
  2. James Sweet

    James Sweet Guest


    That problem is almost always bad electrolytic capacitors near the
    vertical output IC.
     
  3. Engineer

    Engineer Guest

    I had an old Zenith a long while back with no vertical adjustment pot
    on the outside - but there was one on the inside. I opened it up and
    pushed a 3 inch or so length of PVC tube over the pot spindle (one
    size fitted, 3/8 in, I think.) Then I drilled a hole in the back so
    that the PVC tube poked out - voila! An accessible adjustment - worked
    fine.
    A bigger problem is horizontal scan - most TVs overscan horizontally
    and require the vertical to overscan, too, to get good circles. I've
    never found a good way to set the horizontal scan... unlike computer
    CRTs.
    Cheers,
    Roger
    PS. Usual disclaimers about dangerous TV voltages - if you don't know
    don't do it.
     
  4. Jerry G.

    Jerry G. Guest

    The problem is usually caused by electrolytic capacitors in the
    vertical amp section going bad from age.

    Don't touch any adjustments. Have the set properly serviced.


    Jerry G.
    ======
     
  5. Guest

    Thanks to everyone who tried to help except for Jerry G. who assumed I
    didn't know what I was doing so was no help!
    I was hoping some former Zenith tech would have the schematic for this
    model. I'll try the elect caps around the vertical, I already had to
    replace an open one in the sound path sound, so should have looked for
    that too.
    Please note when I say I replaced the IC and the capacitor, I myself
    did it!
     
  6. Jeroni Paul

    Jeroni Paul Guest

    Overscan problems can be due to excessive supply voltage to the
    vertical output. Some power supply designs output higher voltages as
    their electrolytics dry.
    However dry electrolytics get better when warm, so your overscan
    problem should reduce after a while. You should also be looking at bad
    solder joints, open resistors and bad potentiometers.
     
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