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Zenith TV vertical deflection problem

Discussion in 'Electronic Repair' started by Jim Shaffer, Nov 16, 2008.

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  1. Jim Shaffer

    Jim Shaffer Guest

    My girlfriend has a Zenith B27A11Z TV, made in 2000, that has a
    vertical deflection problem. It started as the vertical deflection
    going out from time to time, and if she tapped on the TV it would come
    back. So I said OK, it's probably just a bad solder joint, maybe I
    can look at it sometime. But I never got around to looking at it.
    Now she says that tapping it doesn't fix it anymore. Sometimes
    turning it on and off does, but sometimes that doesn't work either and
    if she turns it on and off too many times it stops working altogether
    until she unplugs it. Now I'm wondering whether it's really a bad
    joint. Of course, she still wants me to look at it. So, are there
    any particular points or components that are known to go out on this
    model, so that I can hopefully get this thing over with as soon as
    possible?
     
  2. Probably still solder connections - both at the vertical output IC and at
    the deflection yoke plug. Should have been tended to sooner - the bad solder
    connections can kill the IC, but it sounds as if the connections just got
    worse since there is still full defection sometimes at turn-on.

    Mark Z.
     
  3. Guest

    I remember that there was a series of Zeniths a few years back in
    which a diode in the vertical circuit would become flaky. It would
    check good with an ohm meter as I recall but would fail
    intermittently. I think it was a black high speed switching diode like
    an NTE 506 about a 1 watt size near the vertical IC. Lenny. .
     
  4. b

    b Guest

    this is an exact scenario which demonstrates the idea you should NEVER
    nurse along an intermittent fault, the reason being that as time goes
    on what starts as a simple cheap fix ends up in a complicated mess.
    Chances are, other components and even the power supply have been
    stressed through repeated powering up and down.
    tell her to get it checked right away!
    -B
     
  5. neon

    neon

    1,325
    0
    Oct 21, 2006
    I guarantee it is not a bad solder joint. My bet is a leaky cap. spry some cool air to find which it is.
     
  6. Jim Shaffer

    Jim Shaffer Guest

    Probably still solder connections - both at the vertical output IC and at
    I finally got time to work on the TV this weekend. Prodding the plug
    and the vertical output chip didn't produce the symptoms. Prodding
    the HOT did, but only after the set had been running for about an
    hour. So I re-heated the connections, and it ran for about 3 hours
    with no problems (although I didn't prod it.) Then it started acting
    up again, same problem as before. (It doesn't completely lose
    vertical deflection, I misunderstood what she told me; it shrinks to
    about half size and jumps.) Putting pressure on the HOT's heat sink
    so as to push it towards the outside of the board makes it work
    properly, but only so long as pressure is maintained.

    So, what do I try next? Should I have completely removed and
    re-soldered the HOT? Or do I have a bad HOT since it only acts up
    when it's been running for a time?
     
  7. b

    b Guest

    a blanket resolder of the line and frame stages is called for. That
    heatsink is flexing the pcb so it could be any one of dozens of joints
    in that area. check also the connections to the scan coils (yoke)
    As you suspected, it's best to remove old solder from the HOT and
    replace, though i doubt this is your problem.
    you can make a desolder braid effectively with some old 75 ohm coax
    cable dipped in solder flux.

    work with a good lamp and check the PCB print for any cracks.

    -B
     
  8. b

    b Guest

    a blanket resolder of the line and frame stages is called for. That
    heatsink is flexing the pcb so it could be any one of dozens of joints
    in that area. check also the connections to the scan coils (yoke)
    As you suspected, it's best to remove old solder from the HOT and
    replace, though i doubt this is your problem.
    you can make a desolder braid effectively with some old 75 ohm coax
    cable dipped in solder flux.

    work with a good lamp and check the PCB print for any cracks.

    -B
     
  9. I once fixed a Magnetbox with intermittent vertical tearing, turned out to
    be a loose crimp on a tiny pot. Sometimes components fracture or stretch
    with age, not just solder joints.
     
  10. Guest

    did you look for the diode? Lenny
     
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