Befroe you send the tX back, try replacing the Tx crystal if it is not a synthesized unit. They get bumped about quite a bit and most pay little attention to it. The crystals (in any makers tx) are known to jsut suddenly give up ocasionally. That or a small crack in a crystal can drive you nuts looking for something in the plane. Also try extending and completely cleaning the antenna. Last thing to look at is the antenna connection inside the Tx case. That's about all the easy, do at home, stuff.