RE: Spektrum DX-7
Richard,
You seem to have eliminated low battery voltage as the source of your problem. If the plane is in good enough condition to give it a range check that would be the next item on my list before sending the equipment back to Horizon. Ideally I would do the test with the aircraft facing me and the engine running. Make sure the plane is securely tied down. Since the ground range, even when the bind button is held, is likely to be more than 100 paces, point the transmitter antenna directly at the plane. Get far enough away so the receiver goes into failsafe. If the engine doesn't go to idle or the rudder starts flapping, you have something to work with. If everything works properly, you got a mystery on your hands. Good luck.
Allan