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Hot switching a VGA signal

Discussion in 'Electronic Repair' started by [email protected], Aug 30, 2013.

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  1. Guest

    I'm installing two security type DVR's that each have a VGA output. I would like to use one monitor with an AB switch, and switch between the two VGA DVR outputs. Can I damage anything with such an arrangement? Thanks, Lenny
  2. As long as the DVRs will always output a signal even if no monitor is
    attached, there should be no problems. VGA stuff is birectional, although
    not everything interrogates the monitor.

    Even those rediculous beige steel boxes with the black knob would probably
    be ok for the resolutions coming out of a security system.
  3. As far as I know, no monitor can be damaged by yanking the input signal. So
    the "burp" while switching shouldn't be a problem.

    The only way that I know of that a monitor can be damaged is if it's a
    multi-sync model, and it's driven at a scan rate above its highest spec'd
    rate. Other than that...
  4. That sounds more like legend. I had a couple of Ball Brother open frame
    small monitors that I used back then, for my OSI Superboard and then my
    Radio Shack Color Computer. They needed a horizontal sync signal to
    generate the horizontal ramp (and the very high voltage), but if there was
    no horizontal sync signal, nothing bad could happen.

  5. Okay, that's more defining. I wasn't sure if this was something you saw,
    or something someone else said was true. A bit of information can be
    worse than none at all.

  6. mike

    mike Guest

    For convenience, it's hard to beat a KVM swtich.
    I had a 4-monitor KVM. Switch button on the front
    or hook up a keyboard and hot-key select.
    Oughta be a zillion of 'em at surplus outlets.
    The Two-port ones are a dime a dozen if you live in an
    area with garage sales.

    Also maintains signal continuity so you don't get
    ghosting with long cables.
  7. Leif Neland

    Leif Neland Guest

    Michael Black formulerede lørdag:
    I once had an *old* tube TV-monitor (from a TV station control room).

    I had it connected to a Sinclair ZX-81, which use the CPU for also
    generation the video signal.

    The ZX-81 could be put in "Fast" mode, where it used all the CPU-time
    for computing instead of video generation, so the video was not proper

    This unsynchronized signal probably had a higher flyback frequency or
    something, causing the high voltage to go bananas, so sparks flew,
    which produced large bangs from inside the monitor.

    When the monitor finally died, it got replaced with a B/W tv, where I
    cut a trace from the tuner and applied the video signal to the pcb.

    This ZX-81 later got fitted into a rack, with a wirewrapped 64Kb
    expansion ram and 6 channel audio. Even later, the CPU lived on in a
    CP/M-plus system with a whopping 3/4 MB ram. But that's another story.

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