Most of these controllers use metal contacts to connect to the copper plates on the transmitter circuit board. Sometimes these contacts become disconnected (due to several reasons). A way to fix such a problem is to unscrew the transmitter and take out the circuit board. Now you can either bend the metal contact towards you or screw the circuit board in closer by clipping off some of the screen poles and then screwing the board back in the motor body. But for other issues, you may need to adopt different procedures. You either search DIIY tips for the specific issue you face or consult an expert for assistance.