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Panasonic 27" Squashed Picture

Discussion in 'Electronic Repair' started by [email protected], Feb 13, 2006.

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  1. Guest

    Hey guys,
    I have a 1992 Panasonic PC-29XF10A 27" TV.

    Since about 2 days ago, a ~2" black bar appeared at the bottom of the
    picture and the remaining picture on top of that is compressed
    (squashed) vertically.

    Does anybody have an idea of what components went? And how to figure
    out which ones to replace?

    Haven't repaired any TV's so I am a bit lost when looking inside of
    one, so if anyone can help me in terms of physically locating the area
    that went, that would be great. Or if anyone has a diagram or
    component #'s for that specific model, that would be even better.

    Also, what's the proper way of discharging TV caps?

    Thanks guys,
    Jim
     
  2. Guest

    ESR meter check the electrolytic capacitors in the vertical output
    stage and ramp generator.
    Optional to simply jump the capacitors while tv is running on an
    isolation transformer to find the culprits.
     
  3. Jerry G.

    Jerry G. Guest

    By the way you are asking, you'd be best off to give the set out for
    proper service. The set has to be properly troubleshooted to determine
    the cause. This would require the proper training and troubleshooting
    tools to service. There are serious safety issues when servicing TV
    sets.

    Jerry G.
     
  4. Guest

    The www.repairfaq.org is a great resource of electronics repair
    information and explains safety procedures, including how to discharge
    capacitors. The most likely capacitor hazard is the picture tube
    itself, so don't unplug the thick cable going to the rubber cup on the
    side of the tube. Also don't ignore the hazard of the fragile glass
    picture tube shattering because TVs tip over very easily, usually
    forward.

    A local library may carry Sams Photofacts (no apostrophe in "Sams")
    repair manuals, but Panasonic sells factory repair manuals for very low
    prices.

    Your TV may have a bad capacitor in the main power supply, but far more
    likely a capacitor in the vertical output section is going bad. To
    find the vertical chip, trace the 4 wires leading from the picture tube
    yoke (not the small circuit board that plugs into the end of the tube)
    to the main circuit board, and look up the part numbers of the chips
    near those wires by searching www.nteinc.com, www.bdent.com,
    www.alldatasheet.com, www.datasheetarchive.com, or by simply Googleing.
    I would replace all the electrolytic capacitors connected to the
    vertical chip, but if you need to replace only one, very likely you
    want the ramp generator timing capacitor. Any new capacitor must be
    rated for at least as much voltage as the original, and its capacitance
    value (uF) should be within 20%. Try to get caps rated for 105
    Celcius, not the usual 85C. Watch polarity because installing a
    polarized cap backwards can cause it to short and go bang.

    I hope your desoldering skills are good because you don't want to
    damage the circuit board. Use a 30-40W iron (40W is better) with a
    very clean tip and narrow (.05-.08" wide) copper desoldering braid.
    Cut the braid right after it absorbs solder. If the solder won't wick
    up completely, then you either need a more powerful iron (don't exceed
    50W), a cleaner tip, or should add fresh 60/40 tin/lead solder and
    start over. Practice on a junk board first.
     
  5. Dave D

    Dave D Guest

    By far the biggest shock hazard in any TV is the mains filter capacitor,
    potentially instantly fatal if discharged across the body. The CRT charge is
    a minor inconvenience by comparison, an unpleasant whack/jolt.


    Dave
     
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