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Servo Motor Repair

Amptron Servo Repairs involve

  • AC Servo Motor Repair

  • DC Servo Motor Repair

  • Brushless DC Servo Motor Repair

  • Permanent Magnet AC Servo Moto Repair

  • Permanent Magnet DC Servo Moto Repair

  • Spindle Motor Repair

  • Stepper Motor Repair

  • Encoder Repair

  • Resolver Repair

  • Tacho Repair

  • Servo Drive Repair

  • Servo Amplifier Repair

  • Servo Controller Repair

Common Servo Motor Failures

Servo motors are very complicated and complex due to the fact that lot of mechtronics go into their making. To ensure a successful servo motor repair, you need to be proficient in all areas of electro-mechanical repairs and electronic repairs. Here are some common problems which servo motor failures can be attributed to.

Mechanical Failures/faults. These can be summarized as:

  • Bearings and bearing housings.

  • Contamination caused by grease, oil or cutting fluid inside the motor.

  • Contamination caused by grease, oil or cutting fluid inside the motor brake.

  • Shaft keyway or coupling failure.

  • Rotor magnet failures.

  • Imbalanced rotors.

  • Motor brake wear and tear.

  • Wornout brushes or commutators (DC types).

  • Carbon build up (DC types).

Electrical Failures/faults.

  • Motor winding failures.

  • Brake coil failures.

  • Shorted wiring connections.

  • Faulty connections or broken wiring connections.

  • Electromechanical tachometer sensor faults.

Electronic Failures/Faults.

  • Bearings/bushing failures

  • Encoder output or position count faults.

  • Encoder misalignment.

  • Encoder Memory corruption or breakdown.

  • Electronic Tachometer sensor faults.

  • Memory battery failure.

  • Resolver winding or mechanical failure.

  • Faulty components on PCB’s.

  • Op-amp failures.

  • Driver IC failures.

Specialized Electromechanical skills are needed to repair Servo Motors

Servo motors are very accurate, special and precision motors. They have both precise mechanical and electronic components. Accordingly Servo Motor Repairs require a specialist set of mechtronic skills (electronic, electrical and mechanical) and specialized test rigs and facilities.

Amptron are unique in that we are a fully integrated electromechanical and electronic repair centre with a servo repair department and electronics repair department. We are dynamic in our approach and are continually improving what we do through investment in training and equipment to keep pace with ever changing technological field.

Repairs to Servo/Stepper motors with different repair teams for each discipline or in different departments or work sites can be disastrous as faults will be missed and repair times will be longer. Servo motor operation is a closed loop system wherein the feedback unit (encoder/resolver/tachometer sensor) sends a signal to the drive/amplifier for correction of position and torque and only a qualified, knowledgeable, dedicated and professionally proficient engineer/technician can do successful, reliable and cost effective servo repairs who fully understand these devices.

A technician needs to be proficient in all areas of electro-mechanical repair and electronic repair to perform reliable and successful servo motor repairs and stepper motor repairs.

In addition to the faults/ causes of servo motor breakdown mentioned above, there are a whole lot of issues with a servo motor breakdown. For example, a servo motor that is noisy in operation can be due to:

  • A bad bearing

  • A noisy tachometer

  • A worn or loose encoder, resolver or tachometer mechanical coupling

  • Misalignment of the encoder, resolver or tachometer

  • Broken screen on the encoder or resolver cable

  • Low output from the resolver

  • Loose brake disc

  • A broken rotor/stator magnet

  • Incorrect brake air gap clearance

  • Bad grounding connection in the connector

  • Contamination in the air gap between rotor and stator

All of the above conditions can cause unusual noises inside a servo motor. The need to have a dedicated team that fully knowledgeable about servo motor repairs and can quickly diagnose and isolate these unique faults and repair these motors successfully need not be over emphasized.

Amptron has a specialist servo engineering team to perform mechanical and electronics repair work. We have all the necessary tools and knowledge base to efficiently and effectively perform servo motor repairs.

An in depth understanding of how servo systems and feedback devices work is essential. Servo motors come in a variety of feedback systems: (encoder-incremental or absolute, resolver-single turn or multiturn or tacho sensor) is incorporated in a typical servo motor? Further these can be one or a combination of the following;

  • Incremental Encoders.
  • Slotted optical or hall-effect commutation sensors.
  • Absolute Encoders.
  • Sine wave output encoders
  • Serial Data Encoders (En-Dat, SSI, OEM Specific codes).
  • Serial Data Encoders with model, data, parameter and position memories.
  • Multi Turn encoders.
  • Resolvers.
  • Tachometer generators, digital (electronic) or analog (electromechanical).

Each type of feedback device requires different alignment and test equipment specific to each manufacturer. The data output from these feedback devices can be in a variety of forms, from simple “A & B” quadrature outputs or parallel outputs to bi-directional serial communications in binary, hexadecimal , gray or an OEM specific code. This data needs to be checked and verified to ensure the feedback unit is working properly and is correctly aligned relative to the rotors magnetic field. Amptron has built specialist test equipment to read the data and run the motor at its working speed where the feedback data is in a specialized communication form specific to the OEM.

Magnetizing a Servo Motor/Stepper Motor

Even the mechanical repairs to a servo/stepper motor need specialist equipment. Rotors should never be removed from a servo motor by hand. Dragging the rotor magnets over the stator will cause damage to them as they are often very brittle. Similarly on stepper and pancake motors repairs magnets are demagnetized and re-magnetized during disassembling and re-assembling to ensure proper torque.

Correct alignment of feedback devices is crucial, Amptron has built its own test rigs with OEM drives, to align encoders, resolvers, commutation sensors etc to the manufacturers specifications.

Dynamic Load Testing a Servo Motor after Repairs

The most critical and sensitive aspect of a servo motor repair is the ability to load test and verify the operation. Ability to run a servo motor after repairs is the absolute minimum for testing. Servo motors will not run on a standard three phase supply, you can destroy the magnets that way. Amptron has specially built motion controller/drives on rigs to run test repaired servo motors to simulate the conditions that would be seen on a robot or a CNC machine. We use this method of testing for Siemens Servo Motors, ABB Servo Motors, Bosch Servo Motors, Indramat Servo Motors, Control Techniques Servo Motors, Kollmorgen Servo Motors, NUM Servo Motors, Reliance Servo Motors , Allen Bradley Servo Motors, Baldor Servo Motors , Lenze Servo Motors, Emerson Servo Motors and many more brands.

Fanuc, Kawasaki, Yaskawa, Sanyo Denki and Nachi servo motors require more complex methods of testing, i.e. as these motors communicate directly with the machine controller and not the drive. We have designed, developed and prepared our own equipment and rigs to meet the specific test requirements for these motors and run test these at rated speed and torque.

Lastly, to test and verify a servo motor it needs to be run against a dynamic load. Amptron uses its own designed and built dynamic load rig. We have the capability to run a servo motor through a motion controller, against a changing load similar to the conditions that would be encountered on site. This test is critical as the motor reaches its operating temperature where it’s operating performance at its rated load and power output can be monitored. Parameters like motors torque constant back EMF constant are monitored at this stage.

We, at Amptron, also do a full test of any brake fitted to the motor using the same load test facility. We can apply a load to the brake and measure the point at which slippage occurs.

New and more complex servo motors are coming to the market every year. Servo motors are complicated; and Amptron is a Servo Motor Repair specialists. Major OEM’s put their confidence in us to repair and utilize our servo repair services their motors. We are now repairing thousands of servo motors. We are dynamic in our approach and are putting resources (manpower and monetary) to continually enhancing our professional knowledge and expertise to be able to remain one the most preferred servo motor repair specialists in North America.

If you want any further information on servo motor repair, just call us at 1-800 504-9996 or email us at

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