Perhaps the slider control on the transmitter is the problem. Try plugging in the elevator or rudder servo into channel 3 (motor control) on the receiver and see if you can control them via the slider. I don't think it's likely that only one channel in the receiver would be faulty. Also, if you can reverse your servos, try reversing channel 3. I had to do this with my Futaba gear to enable motor control. Good luck with your trouble shooting.