Never would have thought to look for a bad crystal unless the Rx. was in a few crashes maybe. On the battery condition before each flight, an easy way to check this to have a Voltwatch installed in each plane. You just look at the LEDs and see what color is lit up. One of these saved my Sea Fury once. Batterys were reading good until I landed after a 3d flight. The green lights were out, only the red one at the end was on. Turned out the pack had a bad cell in it. Cheap insurance and I install them under the canopy in all my new planes. [8D]