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tv: vertical jitters

Discussion in 'Electronic Repair' started by Herb, Apr 5, 2007.

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  1. Herb

    Herb Guest

    I have an Apex 19" TV here, only three years old. It's been occurring
    that the picture gets vertical jittering (and looks slightly washed
    out) for maybe half a minute - then it gives one big jump and then
    it's okay for a long while.

    Also, symptoms are progressing. From time to time, the picture gets
    reduced down vertically, so that it looks like letterbox format and it
    is also very washed out. Then it gives one big jump and then it's okay
    for a while.

    The newest thing is that sometimes when I turn it on, it displays only
    a blank screen - no picture and no sound whatsoever. I have to
    repeatedly turn off/on until it works again.

    Is this a failing capacitor? How can I proceed to try and fix it?
    Thanks.
     
  2. James Sweet

    James Sweet Guest


    When capacitors start to fail, the problem usually gradually improves as
    the set warms up. In this case I'd be more inclined to suspect solder
    joints or a semiconductor. A can of freeze spray might be helpful in
    diagnosing it.
     
  3. ian field

    ian field Guest

    The combination of jitter and washed out picture might suggest a bandwidth
    or gain problem in the IF circuitry, but the intermittent aspect of the
    symptoms you go on to describe suggest more likely failing of lead-free
    solder in the V-O/P stage, a re-work of the soldering in this area is
    probably the quickest and easiest thing to eliminate a possible cause. If
    that doesn't cure it, warming various areas of the panel with a hairdryer as
    already suggested might give a clue to capacitors with ESR problems, before
    I bought an ESR meter I had devised a variety of means to weed these out, in
    PSUs faulty caps often run hot while smaller caps in signal stages were
    often sensitive to gently twisting them on their leads. One very useful
    instrument I still keep handy is a Steinel continuity checker, it has an
    inverse parallel pair of LED, a battery and a thin film PTC thermistor so
    the test current starts briefly high and decays to a suitable value for one
    or the other of the high efficiency LEDs, With the suspect cap out of
    circuit, the tester would give a short flash as the cap charged - then if
    the button was released the other LED would flash as the cap discharged -
    caps with ESR problems caused the flash to visibly "ramp up" before decaying
    again.
     
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