> >
> > Oscilloscope load is typically of the order of 1 Mohm and 10 pF. It 
> > can affect oscillator operation under marginal conditions 
> but usually 

Depends on the probe type and brand (quality).  Also some dependence on
how the probe has been treated over its lifetime.

X1 probes can be as low as 100kOhm and in excess of 50pf for cheap crap
probes but should be 1M || 20pf (or lower)

X10 probes are typically 10M || 15pF

Active FET input probes (home made or store bought) can have very much
higher input impedance and ultra low capacitance, on the order of 10s of
pA or better.

Looking at a crystal oscillator, a x1 probe will probably shift the
crystal's operating point.  A x10 may still shift the crystal but it is
a little bit less likely, especially if you solder on short test wires
for the signal and also a loop for the ground sleeve on the probe.
Don't clip on and don't use the 6" ground lead.  And active probe with
FET input is much less likely to cause a shift or othewise affect the
crystal.

Rob

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