One of the things we do here in our avionics shop when looking for intermittant conditions is to operate the equipment while vibrating it and/or tapping on it. Quite often this will turn up a loose or damaged part. Doesn't catch them all of course. Tapping on his crystal may have revealed the problem, maybe not. A hard crash deserves a hard look at the electronics and you have to decide between a repair/inspection bill and the cost of new equipment.
Sorry for the loss. [&o]