You sure the buddy box (slave) students box, whatever, wont work with the crystal out and or the battery removed? I thought with the trainer switch held to the trainer position all you were doing was using the gembals on the students box (the one the student holds) I sure at the old field I flew at we had a buddy box with out a crystal. Are you using JR?
Antway thanx for posting the important thing to stress.... as i did to my students "leave your box off"