Crystal failures are always a problem. We used to chuck a bag of them in a tumbler for an hour then on a tray on a vibration table for an hour. About 20% would fail on test from being entirely open circuit to being way off frequency.
That's physically almost impossible. Even if the crystal sheet were to drop off the mounts it would have to do something electrically hard to explain to cause a short. The contact areas are usually the only conducting parts on the crystal itself. Failing open is easy for the exact same reason: if the crystal is mechanically damaged that will usually dislodge one or both of the contact areas. This is because those are the only places where something touches the crystal to give it as much freedom to vibrate as possible, any kind of further constraint would impede function.
I used to find that the crystal filters used in certain VHF radios would fail after as few as a couple of hundred hours if they were mounted a certain way in certain machines. I always assumed that it was down to some particular vibration frequency from the engine coupling through the cab.
Although that was nothing to the amount of 0.1μF SMD ceramic capacitors that would go leaky in the same product, and cause all sorts of bizarre faults like drastic loss of sensitivity (decoupling capacitor in IF amp bias circuit pulling down the bias rail) or sensitivity being okay but radio not going into service because the squelch would never open on the control channel (decoupling capacitor in the squelch threshold circuit pulling down a different bias rail).
Bloody things. Fine when they worked, not too horrible to work on when they didn't, at least.
sdcfgy · · focus · HN ↗
snvzz · · focus · HN ↗
sdcfgy · · focus · HN ↗
snvzz · · focus · HN ↗
And if you touch the board, applying pressure just right around the area, it actually does produce a clock.
(the output is not even connected, only my oscilloscope at the other end of the trace)
I will probably try and re-solder the oscillator next.
jacquesm · · focus · HN ↗
ErroneousBosh · · focus · HN ↗
Although that was nothing to the amount of 0.1μF SMD ceramic capacitors that would go leaky in the same product, and cause all sorts of bizarre faults like drastic loss of sensitivity (decoupling capacitor in IF amp bias circuit pulling down the bias rail) or sensitivity being okay but radio not going into service because the squelch would never open on the control channel (decoupling capacitor in the squelch threshold circuit pulling down a different bias rail).
Bloody things. Fine when they worked, not too horrible to work on when they didn't, at least.