"Dave Plowman (News)" wrote in message
...
I have a device where the crystal and associated network is external to
the CPU. Which isn't working. Looking across the two connections with a
scope there's no approx 30 kHz as should be - but what looks like very
dirty mains hum. Any way of easily testing the crystal other than by
substitution?

--
*Why is the man who invests all your money called a broker? *

Dave Plowman London SW
To e-mail, change noise into sound.


The easiest test that I can think of is to breadboard a CMOS oscillator circuit.
Use one inverter out of a hex inverter like this:

View in a fixed pitch font such as Courier

|\
+--| 0---+---- OUT
| |/ |
| |
+--\/\/\--+
| 1 Mohm |
| |
| \
| / 2.7 kohms
| \
| /
| |
| Xtal |
+---|[]|--+
_|_ _|_
55pf ___ ___ 60pf
_|_ _|_
\ / \ /

If the circuit oscillates at the crystal frequency, then the crystal is likely
good. If it doesn't oscillate at all, or oscillates at the wrong frequency,
then it's likely bad.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.