I tried to fly my Phantom 1 today for the first time in several months. I tried to get the Zenmuse gimbal to work with it last fall, but was unsuccessful and decided to wait for the Phantom 2+. Today only 1 of the rotors would spin. The GPS calibrated without difficulty. I took the Phantom apart and disconnected all of the cables to the Naza. I then followed the video online for the Phantom upgrade to make sure all connections were correct. I then tried to fly again but this time 3 rotors worked, but one rotor did not. All of the connections and solder joints looked good. Any suggestions on what to try next?