Servo Drive Troubleshooting

Servo driver is a kind of controller used to control the servo motor, which belongs to the servo system. When some problems accur as follow of a servo drive, how we should test and repair? Here are 6 tips to to maintain a servo drive.

1. When the oscilloscope checks the current monitoring output of the driver, it is found to be all noise and cannot be read out

Fault reason: Current monitoring output is not isolated from AC power supply (transformer).
Treatment method: It can be observed by DC voltmeter.

2. The servo motor runs faster in one direction than the other

• Failure cause: Phase error of brushless servo motor.
  Treatment method: Test or check the correct phase position.
• Cause of failure: Test / deviation switch is in test position when testing is not used.
  Treatment method: Open the test / deviation switch in the deviation position.
• Failure cause: Wrong position of the deviation potentiometer.
  Treatment method: Reset.

3. Servo motor stalls

• Failure caise: Polarity error of speed feedback.
  Treatment method: You can try the following method.
  a. Place the feedback polarity switch to another position if possible (some drivers can).
  b. If you use a tachometer, switch on the TACH+ and TACH- on the drive.
  c. If the encoder is used, the ENC A and ENC B on the driver will be switched on.
  d. For example, in the HALL speed mode, swap the servo drive on the HALL-1 and HALL-3, and then switch on Motor-A and Motor-B.
• Failure cause: The encoder power is lost in encoder power feedback.
  Treatment method: Check connection 5V encoder power supply. Make sure that the power supply provides enough current. If an external power supply is used, it should be guaranteed that the voltage is on the servo drive signal.

4. The LED light is green, but the servo motor doesn't move

• Failure cause: Motor prohibition in one or more directions.
  Treatment method: Check +INHIBIT and –INHIBIT ports.
• Failure cause: The command signal is not on the driver signal.
  Treatment method: The command signal ground is connected to the servo drive signal ground.

5. After power on, the LED light of the servo drive is off

Failure cause: The power supply voltage is too low, which is less than the minimum voltage requirement.
Treatment method: Check and improve the power supply voltage.

6. When the servo motor rotates, the LED light flashes

• Failure cause: HALL phase position error.
  Treatment method: Check whether the servo motor phase setting switch (60 degrees /120 degrees) is correct. Most brushless servo motors are different of 120 degrees.
• Failure cause: HALL sensor failure.
  Treatment method: When the servo motor turns, the voltage of Hall A, Hall B, Hall C is detected. The voltage should be between DC 5V and 0.

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