Your Guide to the Servo Motors Repair Process

Garage Adjustment Repair Car Motor Vehicle Concept

Repairing a servo motor is not an easy thing to do. Only a few people actually have the skills and the patience to do it properly. For those who don’t know, AC servo motors are electric motors that have encoders, which are used by controllers to allow for closed loop control or to give feedback to these motors. It is also these encoders that make repairing servo motors very tricky. For a motor to be repaired, it has to be realigned. Without realignment, it’s pointless to try and fix it.

The reason why businesses rely on accredited specialists to repair their AC servo motors is because the alignment system used is both expensive and complex. Repairing an AC servo motor requires a few key steps. Before anything is done, the motor in question is first checked for its model number, serial number, and its unique GES number. It is also encoded into the repair company’s database to ensure that it can be easily tracked. To help you understand all the steps involved in the entire repair process, read on.

Initial evaluation

The repair process begins with the checking of the motor in question. All parts are checked, including the keyway, the shaft, the end bells, the connectors, the terminals, and the terminal box. Once the inspection is done, a short test or surge comparison test is performed. This will help determine if rewinding is needed. The other tests to be done are:

  • Insulation resistance test or megger test to check for insulation issues
  • Balance test using an root mean square (RMS) meter to determine if windings are balanced and not grounded
  • Brake verification for motors with brakes
  • Kinetic energy (KE) test to determine magnet conditions
  • Feedback device test using the TI-5000 Mitchell Electronics System
  • Count test which is done by manually turning the shaft while connected to the system

After the evaluation stage, the extent of the damage is determined and the type of repair needed is plotted. The findings are sent to the customer along with recommendations for repair and a quote. Once the approval for repair is received from the customer, the next step ensues.


This step in repairing AC servo motors includes the motor being taken apart piece by piece, starting with the backplate. Next is the encoder and its housing, as well as its wiring system. The parts that are next removed from the assembly are the end bells, the rotor, and the bearings. In this step, these parts are individually inspected to see if any of them needs to be replaced. The last part to be removed from the motor is the brake.


To ensure that no debris is left in the motor after it is reassembled, all the parts are put through a cleaning process, which uses alkaline washing instead of pressure cleaning or hand washing. It has been noted that this method cleans the motor parts better.

Bearing change

This is a step that has to be done every time a servo motor is repaired, since a faulty bearing can cause motor failure. When the bearing has been replaced, the servo motor is then put back together.

Final testing and tuning

No AC servo motor is totally repaired until it is tested, realigned, tuned, and checked for accuracy. This is where the TI-5000 Mitchell Electronics System is used. The tests that are done to the repaired AC servo motor include the following:

  • RPM Test
  • Encoder alignment test
  • Memory test
  • Complete full-load test

Once testing is concluded and everything is in order, the motor is then wiped down and repainted. Once the paint is dry, the motor is prepped to be returned to the customer, almost as good as new. The whole repair process can be tedious and highly detailed, which is why only an accredited AC servo motor repair company can properly do it.