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Damaging computer monitor with wrong input?

Discussion in 'Electronic Basics' started by [email protected], Feb 17, 2007.

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  1. Guest

    I'm working on an output circuit from a computer which outputs two
    different kind of signals according to which mode it is set to (colour
    low/medium resolution or monochrome high-resolution):

    Mono mode : 35.70 KHz horizontal, 71.2 Hz vertical
    Colour mode: 15.75 KHz horizontal, 50-60 Hz vertical

    Is it possible to damage a monitor if it receives signals outside of
    its intended range?
  2. Gibbo

    Gibbo Guest

    I think I am right in saying that older monitors would sometimes fail
    (often with a bang) if fed an input with too high a line frequency.
    Later monitors simply either ignore it or shutdown.

    So it depends on your monitor.
  3. Baron

    Baron Guest

    Short answer ! Yes. Most modern monitors are intelligent enough to
    recognise an out of range signal and display an error message! Older
    ones are not !
  4. Guest

    That's good and bad news.
    The computer is an Atari ST and I intend to make it work with both the
    custom Atari monitors and normal VGA monitors. Sounds like it could be
    risky business to connect the Atari monitors (the Atari ST is a mid
    80s - early 90s computer) to the new output without first making sure
    the mode is correct for that monitor.
    When you say they often go out with a bang -is that permanent failure
    (as in throw it away, the CRT and everything is gone), or is it "just"
    a matter of replacing some components around the signal input stage?
    Anything that can be done to prevent this (in case I or someone
    selects the wrong mode for the connected monitor)?

    Regarding modern monitors I've heard that it's hard to find ones that
    can handle the colour mode of 15.75 KHz horizontal rate -is this true,
    or is it now common for monitors to be able to handle both my output

  5. The flyback transformers went up in flames. The original monochrome
    monitor for the IBM PC would burn if it was powered up without video
    drive. That is why the power supply had the switched outlet than lasted
    till the ATX format arrived.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  6. Gibbo

    Gibbo Guest

    Usually trivial things like the output transistor and associated
    components :) Repairable...... if you know what you're doing, but not
    I'm not sure about this but I don't think you can swap modes on the ST
    without switching it off and back on again. At boot up it looks at the
    13 pin socket to see if it has the "special" monitor attatched, if it
    does, then it fires up in hi res mode.
    The standard colour output of the Atari ST is bog standard European TV
    line frequency. There were *millions* of monitors made with the same
    standard that are now worth about nothing each. Car boot sales are full
    of them. It will work into a scart input on a normal UK TV
  7. YES. As I learned by ordering the Linux OS to display on a monitor
    selected by me horizontal and vertical frequencies.
    The video card responded.
    The lesson ended when a little puff of smoke emerged from the monitor
    telling me that this monitor(RIP) was not up to this resolution.
    "We always learn!" - a Hassidic proverb.


    Slack user from Ulladulla.
  8. jasen

    jasen Guest

    I would expect the transitor that drives the horizontal output
    transformer. and possibly a few other parts near it and the main
    fuse for the monitor.

    if you could double the horizontal scan rate on your colour mode that
    would put it within in range of VGA monitors. this is what VGA cards do
    in "CGA emulation" mode each scan-line is sent twice.

    another option would be a Y connector with a relay (or other circuit)
    driven by a frequency detector so that it only connects the sync lines
    to the apropriate monitor if it sees the right frequency.

    vga monitors will shut down in the absense of sync.
    you may have luck with LCD monitors that support video input.
    try a place that has a satisfaction guarantee....
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