one rotor not spinning

[bdh6a7]

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?

 

[tanasit]

Swap the 2 connectors of the problem motor/ESC and the working one/ESC to the NAZA.
This will test if the ESC and motor combination work on the problem one.
If the problem persists, then either that ESC or that motor is defective which is more likely than the bad NAZA.

Also double check the soldered joint of the 3 wires from that motor to the ESC board because many reported some peeled off!

Good luck