I have recently purchased a used Phantom 3 Professional. The seller said that the item had been tested and worked. I got the item and the gimbal was in bad condition. After taking apart the gimbal, putting back together, and alot of firmware updates, I am having a problem with the yaw arm. Whenever I fly, the video is shakey and has the DJI jello effect. I checked the dampeners and they are intact. I noticed that the gimbal yaw in flight will not move. If anyone has any ideas, please let me know!