Hi Its been a while since i played with one of these ,but if its powering up allowing you to select modes ,but not starting ,I would say Dan is on the right track ,its not sending signal to the RX18 so I would redo  the three wires to the RX18 and check the tracks of these for breaks,its probably a dry solder joint or a broken wire cracked track.But limit your search to these wires and tracks .

 regards pete