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Measuring xtal frequency

Discussion in 'Electronic Repair' started by DaveC, Aug 16, 2003.

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  1. DaveC

    DaveC Guest

    Xtal resonator (see my post elsewhere in this NG) input to custom
    microcontroller is suspect. I'd like to view the frequency signal, but the
    minute I put my scope probe on it everything halts, and only a DC voltage is
    visible.

    I'm presuming that the probe is loading down the circuit such that it stops
    dead.

    How can I successfully view this? Just find a better probe? Any other
    interface tricks I can try?

    No schematic or pin data on the microcontroller, so if there's a "clock out"
    pin I can't find it...

    Thanks,
     
  2. Dave VanHorn

    Dave VanHorn Guest

    A 10x probe may allow it to run, make sure you're on the output side.
    I use a shortwave receiver with BFO, which also allows me to determine
    frequency pretty accurately.
     
  3. Begin by adding 100K-ohm resistance from your test point to your scope probe
    tip. Gradually increase to 2M or 4.7M or so. If is probe loading that
    should prove it. Also, don't use the ground clip on your probe. Short the
    ground collar on the probe tip to a nearby ground with a "greenie"
    screwdriver or other short metal object. The direct ground makes a big
    difference.

    Good luck!

    Len G.
     
  4. Sorry. I didn't mean to do that!

    Begin by adding 100K-ohm resistance from your test point to your scope probe
    tip. Gradually increase to 2M or 4.7M or so. If is probe loading that
    should prove it. Also, don't use the ground clip on your probe. Short the
    ground collar on the probe tip to a nearby ground with a "greenie"
    screwdriver or other short metal object. The direct ground makes a big
    difference.

    Good luck!

    Len G.
     
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