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Crystal load?

Discussion in 'Electrical Engineering' started by DaveC, Feb 12, 2013.

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  1. tuinkabouter

    tuinkabouter Guest

    You can still buy it in germany.
    Standardquarz, Grundton, 8,867238 MHz 0.18 euro (0.24 us dollar)

    Minimum order 10 euro.
    Only drawback is the transport cost :((
  2. rickman

    rickman Guest

    I notice the machine the monitor is sitting on looks like it has a tape
    drive backup in it. What is this a 486 some 20 years old? Yes, the
    earlier monitors were difficult beasts that were very sensitive and
    could even be damaged by running them off frequency. But they haven't
    made that sort of thing for a long, long time. Far too long to still be
    in use. If the OP is actually driving one of those monitors, I would be
    surprised. In that case, the crystal might need to be ±1000 ppm
    accurate. But for any modern monitor it will adapt to whatever you send
    it nearly without limit. Have you worked with a monitor that isn't 40
    years old?

    My point is that for $5 the guy can get some crystals that he can try.
    Otherwise he seems to be having a ton of difficulty finding anything he
    can use. I believe he hooked the board up to a monitor to test running
    it from a signal generator. Did the monitor burn up then? Why don't
    you try getting a little more real rather than busting my chops when you
    don't know what type of monitor he is driving?

    I can't believe you have worked for so long and actually believe the
    crystal driving a CGA board was ±3 ppm accurate. That's an order of
    magnitude more expensive oscillator than what they actually used,
    perhaps two!
  3. rickman

    rickman Guest

    Yes, an old piece of equipment that is in tatters and may or may not use
    the original monitor. That is my point. Until the OP responds, you
    simply don't know what monitor is being used. If he wants to test the
    equipment with a $1 crystal rather than a $50 crystal that will take two
    months to get, that is his choice.

    I'm not going to argue with you about this. The crystals used in PCs
    and nearly all consumer electronics are only accurate to a few 10's of
    ppm and typically are only stable over temperature to roughly the same
    range. You can tune the crystal to an exact frequency with a trimmer
    and it will be off by 10's of ppm by the end of the day or before the
    equipment has warmed up (or conversely after). Did PCs warm up the
    oscillator before turning on the monitor?

    The point is that talking about depending on crystals being ±3 ppm
    accurate is not valid unless it is a more expensive piece of equipment
    that can justify the cost of a temperature compensated oscillator. I
    don't care about how many crystals you have looked at, holding a ±3 ppm
    spec on an oscillator is not something you do with a $0.50 crystal
    oscillator. CGA never had to rely on the timing being anywhere near
    that accurate, period; or any other display I have ever worked with.
    Heck, that is outside the spec of many frequency counters from HP and
    elsewhere! The model HP5383A timebase is specified for 3 ppm/month
    aging, 2.5 ppm between 0°C and 40°C and 0.5 ppm due to power 10% line
    variation. This is a piece of equipment with an accuracy limited by the
    crystal oscillator, so I think they would put a lot more effort into
    that feature than PC makers would in their reference clocks.

    Your claims that CGA monitors (or any others) need to be driven to a
    timing accuracy of ±3 ppm is not supported by the facts.

    Go be rude with someone else!
  4. josephkk

    josephkk Guest

    It is my opinion that you can easily just use the crystal from the Irish
    or German vendor. For some reason that particular frequency is very
    standard in Europe and is mass produced by the millions. Very likely to
    be just fine. The high volume production lowers the price. I doubt that
    the actual frequency is any better than 50 ppm though, and more than 1000
    ppm of frequency error may or may not cause problems.

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