Feedback Repair

Global Electronic Services repairs encoders, tachometers, and resolvers for all servo motor repairs. Feedback repair is necessary to ensure top performance of your servo motor and drive. Feedback devices are engaged to deliver information back to the control and indicate performance relative to many different factors, including:

  • Speed
  • Direction of rotation
  • Position
  • Acceleration rate
  • Deceleration rate
  • Relative position of the rotor to the stator

If you are experiencing deficient performance with your servo motor, it’s time to discuss your needs with us. Global Electronic Services can provide a complete diagnostic and repair for your servo motors using only factory certified and trained technicians.  We use the Mitchell Electronics system to ensure that all feedback devices are properly aligned with the servo motor.

Plus, we promise there are no surprises. We’ll give you a quote over the phone, but when we receive your motor for servo motor feedback device repair services, we’ll perform a thorough check and update what we have provided. You’ll know all the work your motor needs and how we can help.

All this work is backed by an 18-Month, In-Service Warranty so you can rely on the servo motor feedback repairs we perform to keep your operations healthy and stable.

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Absolute Encoder

Our servo motor feedback repair services cover all absolute encoders, which use numerous code rings with different binary weightings to provide a digital data word representing the absolute position of the encoder Absolute encoders for servo motor feedbackwithin one revolution down to the precision of the least significant bit.

Adding more bits will divide one revolution into smaller segments, and the encoder will therefore provide higher resolution. Multiple revolutions may be indicated by additional code discs which are gear driven to give count of multiple turns.

The Absolute Encoder is unique because it will report the absolute position of the encoder to the electronics. It will do this as soon as powered up with no need for indexing. It’s one of the most critical servo motor feedback device repair solutions for any maintenance team to use.

Incremental Encoders

Another important servo motor feedback device for repairs and audits is the incremental encoder. This piece of equipment operates through photoelectric scanning of the fine lines on the rotating disk.

Incremental encoders provide an A and B pulse output. Pulse outputs provide no usable count information in their own right. With an incremental encoder, the counting is done by external electronics. The output on lines A, B and Z are checked with an oscilloscope. Accurate count checks are done with pulse counting device such as Mitchell Electronics.

Servo motor feedback device repair services cover many typical checks with these encoders. Some of the most Incremental encoder for servo motor feedbackcommon verifications we perform include:

  • Check the pulse stream of all wave forms with an oscilloscope
  • Check the relationship of the A, A*, B, B* signals with and oscilloscope
  • Check the Z, Z* signals with an oscilloscope
  • Line level check all lines to verify that none are missing
  • Line count with a digital pulse counter
  • Run at continual count at operating speed check,
  • Measure the offset from signal A to signal B.
  • Measure the “on” versus the time “off” of the pulses.

These tests help our certified technicians ensure your servo motor is brought back up to operational efficiency standards set out by your OEM. That way, you can rely on the servo motor when you need it most, avoiding costly downtime and hazardous malfunctions.

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Serial Encoders

GES works with serial encoders that are able to transfer their information to the control electronics in serial data stream. Serial data provides transmission of the data one bit after the other instead all at once. Serial Serial encoder deviceEncoders are checked by a computerized serial interface, and accurate count checks are done with a pulse counting device such as Mitchell Electronics.

The serial encoder operates similarly to an incremental encoder except that it has additional processing electronics built in to review the data being sent to the control.

Hall Effect Switches

Servo motor feedback repair devices include hall effect switches, which are solid state devices that will output a voltage when placed in a magnetic field. The output will change once the magnetic field is reversed. Sensors are used to return a signal that corresponds to the position of the permanent magnet rotor.

If Hall Effect Switches are positioned close to the rotor, then the signal from the sensors will represent the position of the rotor’s magnets. A majority of Hall Effect Switches provide an open collector or open drain type of an output. The switch acts as a ground and typically does not output any voltage. To have a useful output signal a pull-up resistor must be added.

GES technicians who specialize in servo motor feedback device repair know the proper resistors to add to each Hall Effect switch system in order to ensure that your servo motor is safe and secure.


A Resolver is a rotating transformer, located on the motor shaft. Resolvers may be excited at operating frequency; the sine and cosine outputs may be looked at on an oscilloscope or other testing device for proper levels and change rotation.Electromechanical revolver device for servo motor

Resolvers are electromechanical devices, the resistance of the windings and the insulation of the winding to the ground should be checked. We rewind Resolvers as necessary and then test with full speed at any frequency.

Testing here applies to systems that do not include bearings and are typically used in dirty, oily applications.


All Tachometers are tested by voltage output per the preset RPM’s, polarity and will have neutral tested with its servo motor. If the Tachometer could not be tested before the servo motor was dismantled, then we use a variable speed tachometer test stand. The thermal relays are then checked with an ohmometer.Tachometer for servo motor feedback

Tachometer output and waveform are checked for proper operation. The output value compared to the rate output at the test speed. The ripple contact of a DC tachometer is checked with an oscilloscope. This will indicate the condition of the Tachometer’s commutator, brushes and windings. If the output is from an AC Tachometer then the waveform and time with the hall sensors will be checked.

Global Electronic Services tests waveforms and makes measurements with the Mitchell Electronic Feedback Signal Breakout Box. The breakout box looks for various feedback and counter generated voltages. The typical test points the motor line to line, motor line to neutral, tachometer signals, encoder signals, resolver signals and commutation signals.

Servo Motor Feedback Device Repair Services

When you’re ready to give your servo motors the best repair team in town, reach out to GES. We’ll thoroughly review every motor, part and accessory, so you have a reliable system brought up to OEM standards. Plus, we back up our initial quote with a complete audit — you know exactly what you’ll pay when your servo motor is delivered to us.

Experience our industry-leading customer service today by starting your servo motor feedback device repair service.

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