RE: Changing crystals (same channel)
Here's a long shot if these Rx's are the later 'Z' plug units. The aritronic's Z type plugs (all blue) on the servos along with JR plugs and Hitec (S) plugs which are all compatable Can be plugged in backwards. Even though the plugs have a champhered edge to prevent this its still quite easy to do with any of these brands. If servos are plugged backwards it will cause no damage however nothing will move and give the same symtoms you describe.
John