[time-nuts] Efratom FRK - no 10Mhz oscillator
eb at telight.com
Tue Dec 20 13:21:18 EST 2011
I have some M100s, which are similar, I think. A while back one of
them wouldn't lock, although the oscillator didn't stop. I found a
leaky high-K ceramic cap in the OCXO control loop. I don't have the
correct schematics, so was just shotgunning stuff. I would suspect
those parts and any tantalum caps in that section. I don't think they
used any aluminum electrolytics in this mil-grade gear.
VCOs can stall from inadvertently reversing the polarity on the
varicap diode, causing it to forward bias. In some circuits this is
possible, which turns the varicap from a high-Q capacitor into a load
resistance on the oscillator. You may want to check the loop
conditions (not in a lockup/reversed mode) and make sure the actual
diode tuning signal is in the right range before blaming the crystal.
If not, you can force it and see if the XO starts up.
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