I currently have an inspection robot deployed in a remote part of Africa that has a failing Turnigy TGY-6114MD servo. The issue started happening during normal operation and was working fine previously. Now the servo won't respond to commands unless given a slight push or nudge and then it will move to it's commanded position. We thought there may be some binding in the gearbox. After removing the gearbox and the gears we found that the motor shaft itself needs a slight push to start spinning. So with no load on the motor at all, it still won't start unless given a slight push.
Does anyone know what may be causing this behavior? We are unfortunately unable to get a replacement part in a reasonable amount of time so any repair ideas are welcome!
EDIT: Update. We measured the voltage across the motor electrical connections during operation. When the motor is turning (with no physical load) the voltage is 4.98V. When the motor stops, the voltage drops to 1.4V. On an identical working servo on the robot, the voltage is 0V when the motor stops. What would cause the 1.4V at the motor when stopped?