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Servo drive alarm troubleshooting

Servo amplifier and servo motor alarms by maker and model: Yaskawa Sigma-7, Mitsubishi MELSERVO, Allen-Bradley Kinetix, FANUC and more. Encoder, overload, overcurrent and following-error faults, each with sources.

By servo drive

YaskawaΣ-7 (Sigma-7) SERVOPACK

7 fault-code guides

Mitsubishi ElectricMELSERVO-J4 (MR-J4)

7 fault-code guides

Mitsubishi ElectricMELSERVO-J5 (MR-J5)

2 fault-code guides

Allen-BradleyKinetix 5700 servo drive

3 fault-code guides

FANUCαi series servo amplifier (SVM, PSM)

25 fault codes listed

By symptom

SymptomServo encoder communication error

Why a servo drive loses its encoder (Yaskawa A.C90, MR-J4 AL.16/AL.20, MR-J5 AL.016, Kinetix S43/S45) and how to find cable, noise or encoder faults.

SymptomServo vibration or hum at standstill

Why a servo hums, buzzes or hunts while holding position: gains too high, wrong inertia ratio, resonance or mechanics, with Yaskawa and Mitsubishi checks.

SymptomServo overload alarm

Why servo drives trip on overload (Yaskawa A.710/A.720, MR-J4 AL.50/AL.51, Kinetix FLT S07) and how to separate duty cycle, jams, brakes and wiring faults.

Overview

Servo systems move CNC axes, robots, packaging machines and presses. The amplifier supervises current, voltage, temperature, encoder feedback and position error, and stops the axis with a numbered alarm when any of them goes outside its limit.

Common problems

Encoder and encoder-communication alarms

The amplifier lost or distrusts the motor feedback. Cable damage at flex points, connector contamination, noise from poor shield grounding and a flat absolute-encoder battery are more common than a failed encoder.

Overload and overcurrent

Compare the alarm with what the axis was doing: a jam, a brake not releasing or a crash points at mechanics; trips on fast moves point at acceleration, gains or an undersized motor; trips at enable point at a shorted motor or cable.

Following (position) error

The axis fell behind its command by more than the allowed amount. Check for mechanical binding, torque limits, gain settings and whether the move asks more than the motor can deliver.

Vibration, hunting or hum at standstill

Usually gains that are too high for the load inertia or a mechanical resonance. Note the frequency, whether it changes with position, and the inertia ratio before re-tuning.

Evidence that helps

  • Photo of the amplifier display or alarm screen
  • Amplifier and motor model from the nameplates
  • What the axis was doing when it alarmed
  • Alarm history and, if available, a speed/torque trace
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