from my experience it could be any one of the motors. They all have the same sensors as the Yaw. If you remove them and inspect the senors you may find the bad one. Or it could be the esc could also be bad. Did you inspect the new yaw for scratches on the sensors? New is not always new on EBay.
If you wanted to send the camera to me I would check it out. I can give you an estimate for repair and if it can't be repaired I would just send it back at no charge except for $10 shipping. I have every motor and the esc boards.
Thank you for your reply!
I have fixed my fair share of phantoms and other drones, but not having a pile of known good parts makes it a real guessing game. I am a Vet and worked 15 years as a machinist, so my back ground is to not easily give up on any thing. So before wisdom gets the better of me and I send the gimbal out to some one who already has the parts and know how to fix it...here is what I have tried so far.
Replacing the yaw arm did not go smoothly as the arm I ordered from amazon must not have been of the highest quality, the center recess for the yaw motor to align was off center from the screw holes such that only one screw hole would line up at a time. I ended up enlarging the motor recess to the point where the screw holes mostly lined up again.
This maybe the point where I shot myself in the foot. After tightening the motor screws the motor did not seat perfectly to the yaw arm. I put the assembly in the vise to try and gently encourage a better seat. I heard a single popping sound and though it was just the motor seating in to place. Maybe the popping sound was the sound of something in the yaw motor breaking.
I checked the motor leads for continuity, the three large pads on the ribbon have all make a circuit between one another as they should. I even tried using an gimbal esc from a phantom 4, but still no response from either the yaw or roll motors. In desperation I tried a second gimbal ribbon and even did a firmware update.
I did swap the yaw housing, but did not see any thing that jumped out at me as being off, no obvious damage.
If only one motor is bad, would both the roll and yaw motors fail to work?
Also, where would I be shipping this gimbal to when reason sets in?