monitor problem

Discussion in 'Computer Information' started by Jr., Sep 6, 2007.

  1. Jr.

    Jr. Guest

    My lcd flat-screen monitor is beginning to "flicker".
    I see "wavy" lines especially in the blue portions of the screen.
    Is it dying?
     
    Jr., Sep 6, 2007
    #1
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  2. Jr.

    Paul Guest

    Jr. wrote:
    > My lcd flat-screen monitor is beginning to "flicker".
    > I see "wavy" lines especially in the blue portions of the screen.
    > Is it dying?
    >


    Do the symptoms change, if you adjust the light output of
    the screen ?

    The backlight operates at two frequencies. At a relatively
    high frequency (> 25KHz where it is inaudible), the inverter
    converts 12 volts DC to 700 to 1000 Volts AC, to make the
    compact fluorescent backlight tube light up.

    There are two methods to control the intensity of the screen.
    A simple, limited range of voltage control is possible, and
    that is an analog method of some sort. (That might be used on
    an older monitor.)

    The second method, is low frequency duty cycle modulation.
    The 25KHz behavior is turned on and off at a much lower frequency,
    like 100+ Hz. The duty cycle of the modulation is varied,
    and by doing this, a wider range of CCFL light output is
    possible.

    In terms of the scanning of the screen, the signals present
    on VGA are R,G,B and H,V. RGB are the three colors, and they
    are carried on coaxial wires (signal wire with foil ground
    around the wire, for shielding and controlling the desired
    75 ohm impedance). The RGB signals are virtually useless,
    without synchronization signals. H and V are horizontal and
    vertical sync, and the display of the RGB signal is
    coordinated by the sync signals. The edge of a changing
    voltage level on a sync signal, controls where the RGB is
    aligned to the left edge of the screen. Similarly, the vertical
    scanning (placement of line 1 at the top of the screen), is
    controlled by the second sync signal. If there is any problem
    with synchronization, the symptoms can vary.

    Many people have seen a TV set "scroll" or wave, when sync
    is lost. The old vacuum tube sets, used to have knobs that
    the users would adjust, to stop the scrolling.

    The LCD monitor though, is different. If there is a signal
    problem coming from the video card, certain kinds of failures
    can be recognized by the hardware monitoring done inside the
    monitor. For example, the monitor does frequency checks on
    H and V, to determine whether the scan rate being used is
    within the capabilities of the monitor. If they are not, the
    OSD (on screen display) will appear and give a warning message.
    During that time, to make the OSD image on the screen, the
    monitor will substitute its own control signals, in order
    to make a nice image on the screen.

    Now, if there is a signal level or quality issue with H and V,
    not all possible failure modes may be detected. On the one hand,
    an inconsistently received H or V, might trigger the frequency
    check of the OSD, or it might simply give a crappy picture.

    So when you say "wavy", that sounds to me like a sync problem.
    Either a bad cable is affecting H or V, or a bad video card
    output is affecting H or V. Remove the cable and inspect the pins
    on both ends, for problems.

    I've described both how the light is made, and how the screen can
    be wavy, to get you to comment on whether the problem seems to be
    related to light intensity, or the problem is related to the
    painting of the image on the screen. From a percentage point of
    view, most problems with LCD monitors seem to be with the lighting
    (failed inverter or backlight is becoming dim). There are relatively
    few comments about sync loss.

    Using DVI should give a different set of failure modes, but I'd
    have to look up the encoding method, to suggest ways it could
    fail.

    Paul
     
    Paul, Sep 6, 2007
    #2
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  3. Jr.

    Jr. Guest

    So, how do I figure out if it is the monitor or the video card?

    "Paul" <> wrote in message news:fbpa5v$ev7$...
    > Jr. wrote:
    >> My lcd flat-screen monitor is beginning to "flicker".
    >> I see "wavy" lines especially in the blue portions of the screen.
    >> Is it dying?
    >>

    >
    > Do the symptoms change, if you adjust the light output of
    > the screen ?
    >
    > The backlight operates at two frequencies. At a relatively
    > high frequency (> 25KHz where it is inaudible), the inverter
    > converts 12 volts DC to 700 to 1000 Volts AC, to make the
    > compact fluorescent backlight tube light up.
    >
    > There are two methods to control the intensity of the screen.
    > A simple, limited range of voltage control is possible, and
    > that is an analog method of some sort. (That might be used on
    > an older monitor.)
    >
    > The second method, is low frequency duty cycle modulation.
    > The 25KHz behavior is turned on and off at a much lower frequency,
    > like 100+ Hz. The duty cycle of the modulation is varied,
    > and by doing this, a wider range of CCFL light output is
    > possible.
    >
    > In terms of the scanning of the screen, the signals present
    > on VGA are R,G,B and H,V. RGB are the three colors, and they
    > are carried on coaxial wires (signal wire with foil ground
    > around the wire, for shielding and controlling the desired
    > 75 ohm impedance). The RGB signals are virtually useless,
    > without synchronization signals. H and V are horizontal and
    > vertical sync, and the display of the RGB signal is
    > coordinated by the sync signals. The edge of a changing
    > voltage level on a sync signal, controls where the RGB is
    > aligned to the left edge of the screen. Similarly, the vertical
    > scanning (placement of line 1 at the top of the screen), is
    > controlled by the second sync signal. If there is any problem
    > with synchronization, the symptoms can vary.
    >
    > Many people have seen a TV set "scroll" or wave, when sync
    > is lost. The old vacuum tube sets, used to have knobs that
    > the users would adjust, to stop the scrolling.
    >
    > The LCD monitor though, is different. If there is a signal
    > problem coming from the video card, certain kinds of failures
    > can be recognized by the hardware monitoring done inside the
    > monitor. For example, the monitor does frequency checks on
    > H and V, to determine whether the scan rate being used is
    > within the capabilities of the monitor. If they are not, the
    > OSD (on screen display) will appear and give a warning message.
    > During that time, to make the OSD image on the screen, the
    > monitor will substitute its own control signals, in order
    > to make a nice image on the screen.
    >
    > Now, if there is a signal level or quality issue with H and V,
    > not all possible failure modes may be detected. On the one hand,
    > an inconsistently received H or V, might trigger the frequency
    > check of the OSD, or it might simply give a crappy picture.
    >
    > So when you say "wavy", that sounds to me like a sync problem.
    > Either a bad cable is affecting H or V, or a bad video card
    > output is affecting H or V. Remove the cable and inspect the pins
    > on both ends, for problems.
    >
    > I've described both how the light is made, and how the screen can
    > be wavy, to get you to comment on whether the problem seems to be
    > related to light intensity, or the problem is related to the
    > painting of the image on the screen. From a percentage point of
    > view, most problems with LCD monitors seem to be with the lighting
    > (failed inverter or backlight is becoming dim). There are relatively
    > few comments about sync loss.
    >
    > Using DVI should give a different set of failure modes, but I'd
    > have to look up the encoding method, to suggest ways it could
    > fail.
    >
    > Paul
     
    Jr., Sep 7, 2007
    #3
  4. Jr.

    Paul Guest

    Jr. wrote:
    > So, how do I figure out if it is the monitor or the video card?
    >


    Try the monitor on another computer and see if the problem is
    still there.

    Try a different monitor with the problem computer, and see if the
    same thing happens.

    If you have one, try a different video card cable, as sometimes
    the problem is with the pins on the connector.

    Without test equipment, the easiest way to test, is to swap stuff
    and try again.

    Paul
     
    Paul, Sep 7, 2007
    #4
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