Servo Motor Troubleshooting: Causes & Fixes

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Problems on this page:

Servo motor overheating Noise or vibration from the motor Motor does not turn although the drive is enabled Insulation breakdown or ground fault Bearing failure Coolant or oil getting into the motor Loss of torque or stalling under load Coupling slip or shaft key damage

Servo motor overheating

Hits OEE: Availability

Symptoms: The motor runs hot, the drive trips on motor temperature, or the motor smells of hot varnish.

Continuous load above the rated torque

Compare the actual load with the motor rating and resize the motor or gearbox if needed.

Many fast accelerations in the cycle

Smooth the motion profile or lengthen the ramps where the cycle allows.

Cooling blocked

Clean the motor housing and check the fan on fan-cooled motors.

Wrong motor data in the drive

Load the motor data set that matches the motor on the rating plate.

Prevention: Motor temperature and current trended on critical axes.

Noise or vibration from the motor

Hits OEE: Availability

Symptoms: Whine, grinding or vibration from the motor that was not there before.

Bearing wear

Replace the bearings or the motor.

Loose coupling or mounting

Tighten the coupling and the motor mounting.

Tuning too stiff for the machine

Retune the drive for the mechanics it moves.

Shaft misalignment

Align the motor with the driven shaft.

Prevention: Vibration checks on the route for servo axes.

Motor does not turn although the drive is enabled

Hits OEE: Availability

Symptoms: The drive shows ready and enabled but the axis does not move.

Holding brake not released

Check the brake supply voltage and the brake output.

Motor cable phase open or swapped

Check the motor cable and connector against the drawing.

Torque limit set too low

Check the torque limit parameters.

Mechanical jam

With the axis made safe, check that the mechanics move freely.

Prevention: A start-up check of brake and torque limits after any drive work.

Insulation breakdown or ground fault

Hits OEE: Availability

Symptoms: The drive trips on a ground or earth fault, often after cleaning or in wet areas.

Coolant or moisture in the connector

Dry and reseal the connector and tighten it fully.

Cable damaged in the drag chain

Replace the cable with a flex-rated one.

Voltage spikes on long motor cables

Check the cable length against the drive maker's limit and fit an output filter if needed.

Aged winding insulation

Test the insulation with the drive disconnected and replace the motor if it fails.

Prevention: Insulation tests on wet-area motors at planned stops.

Bearing failure

Hits OEE: Availability

Symptoms: Rising noise and heat at the shaft end, play in the shaft.

Radial load from a belt or pulley above the rating

Check belt tension and the motor's permitted shaft load.

Axial load on the shaft

Take axial loads on the machine, not the motor.

Contamination

Check the shaft seal and protect the motor from coolant.

Bearing currents from the drive

Check grounding and use the measures the motor maker recommends.

Prevention: Shaft loads checked whenever a belt or pulley changes.

Coolant or oil getting into the motor

Hits OEE: Availability

Symptoms: Liquid found in the connector or motor housing, faults after machine washdown.

Shaft seal worn

Replace the shaft seal or fit a motor with a better seal rating.

Connectors not sealed or not tightened

Fit the right seals and tighten the connectors fully.

Motor mounted in the coolant spray path

Shield the motor or move the spray.

Cable gland damaged

Replace the gland.

Prevention: Seal and connector checks on the weekly route.

Loss of torque or stalling under load

Hits OEE: Performance

Symptoms: The axis slows or stalls under load and the drive shows high current.

Load higher than before

Check the mechanics for binding or added load.

Torque or current limit too low

Check the limit settings.

Wrong motor parameters after a swap

Load the correct motor data.

Rotor magnets weakened by overheating

Have the motor tested and replace it if the magnets are damaged.

Prevention: Axis current trended against the cycle.

Coupling slip or shaft key damage

Hits OEE: Quality

Symptoms: Position drifts without an alarm, a knock at reversal, marks on the shaft.

Clamp coupling not tightened to torque

Tighten it to the specified torque.

Worn key or keyway

Replace the key and check the keyway.

Damage from a crash

Inspect the shaft and coupling after any collision.

Prevention: Coupling torque checked after any motor change; axis re-referenced afterwards.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Alarm codes: Kollmorgen AKD fault codes · Yaskawa SERVOPACK alarm codes · Allen-Bradley Kinetix fault codes · Mitsubishi MELSERVO alarm codes · FANUC spindle amplifier alarm codes · FANUC servo amplifier alarm codes

Related equipment guides: servo drive · encoder · electric motor · gearbox · industrial robot · stepper motor · linear actuator

Stop the same fault coming back

Recurring servo motor stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover