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Intermittent focus problems on HP P1100 monitor

Discussion in 'Electronic Repair' started by Michel Gallant, Jul 2, 2004.

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  1. Hi all. I have an HP P1100 computer monitor, which is apparently a
    rebadged Sony GDM-500PS. This is a 21" Trinitron monitor.

    I bought it about a year ago, used. Since then, it's had this strange
    problem, which only occurs rarely, but often enough to be annoying. It
    used to happen only every few weeks, but now it can happen more than
    once a day.

    Normally, the monitor works fine. However, it will sometimes start to
    lose focus. Over the span of a minute or so, it will go from perfetly
    legible to very blurry. All but the largest text is illegible, and
    pictures are recognizable, but detail is impossible to see.

    The OSD is also blurry, so it's not a problem with the video signal.

    It will stay blurry like this for some time (between 2 and 15 minutes),
    then there will be a sharp SNAP noise from inside the monitor and
    everything goes back to normal. The noise is not particularly loud.

    Powering the monitor off and on, or degaussing it with the front-panel
    controls, seems to make the SNAP happen sooner, but this is just my
    observation and purely unscientific.

    I'm suspecting some sort of arcing in the HV circuits, but I'm not
    really sure what to start looking for. All my previous experience
    repairing monitors was low-voltage stuff (bad jacks and switches,
    usually). And yes, I've read the safety section and the HV section of
    the s.e.r FAQ.

    Any help you can offer is appreciated. Thank you!

  2. Bob

    Bob Guest

    Michel Gallant wrote:

    No idea what might be wrong with your monitor, but I did have an
    intermittent arc / snap from a cheapy 15" monitor on my server, where the
    screen size would change, along with position. Turned out a large
    capacitor, (.33uF/600V or so) had failed, partially cooked, and the heat
    unsoldered one lead, so it was making intermittent contact. The amazing
    thing was, I had a replacement in my collection of parts.

    With the power unplugged, and after letting the monitor sit for quite a
    while, I'd give the circuit boards a good examination first - you might spot
    a discolored cap or other component. Or carefully check the foil side of
    the circuit board(s) for any discolored / bad solder connections, or dark
    traces / tracking where it's been arcing.

    Good luck,
  3. Might be a dirty or noisy focus control. It will likely be one of two
    little "knobs" sticking out of the HV transformer assembly, and will be
    locked in place with some kind of lacquer.

    Look under the dust for labels; they'll probably be molded into the
    plastic. Give it a few rotations to wipe it clean, and then refocus.

    Watch out for the HV; use a plastic tool (or at least a screwdriver with
    a big plastic handle) to rotate it while the power is on.

  4. Thanks, I'll start looking for zapped bits on the board.

  5. Isaac Wingfield wrote:
    Thanks for your advice. I do have a plastic flat screwdriver that was
    part of a kit I bought on sale at Rat Shack a while ago. Hopefully it's
    the right kind.

    Do you think the "snap" I'm hearing is arcing inside the focus control?
    Is there a lot of voltage across it? Thanks.

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