The "phase sequence" of power incoming line is incorrect. Due to the synchronization problem between the trigger pulse and the main circuit of SCR servo driver, there are strict requirements on the "phase sequence" of the input power supply. If the "phase sequence" is not correct, connecting the power supply may immediately cause the fuse of the main circuit of the driver to blow.


Excessive load caused by mechanical failure. Too much friction resistance of worktable, phenomenon caused by poor gear engagement, interference and collision between workpiece and machine tool, and "locking" of mechanical parts may cause excessive load. In case of the above faults, it can be further judged and confirmed by disconnecting the connection between the motor and the mechanical transmission system and measuring the actual working current of the motor.


Unsuitable cutting conditions. Such as machine tool cutting amount is too large, continuous heavy cutting and so on.


The drive failure. For example, the components of the control unit are damaged, the setting end of the control board is set incorrectly, and the potentiometer is adjusted improperly.


Wrong connection between driver and motor. If the speed negative feedback is connected to the positive feedback, the servo motor will float or the system will be in the oscillation state.


 Improper selection of motor or bad motor. Such as: due to long-term work or other reasons caused by the servo motor "demagnetization", resulting in excessive excitation current: there is a local short circuit in the motor winding, resulting in the driver fuse fusing.


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

Reason: the current monitoring output is not isolated from the AC power supply (transformer).

Treatment method: it can be detected and observed with DC voltmeter.


The motor runs faster in one direction than in the other

Reason: the phase of brushless motor is wrong.

Treatment: detect or find out the correct phase.

Cause of failure: the test / deviation switch is in the test position when it is not used for test.

Treatment: turn the test / deviation switch to the deviation position.

Cause of failure: the position of deviation potentiometer is incorrect.

Treatment: reset.


Motor stall Reason: wrong polarity of speed feedback.Treatment :

  1. If possible, turn the position feedback polarity switch to another position. (on some drives)
  2. If the tachometer is used, switch the tach + and tach - on the drive.
  3. If the encoder is used, switch the enca and encb on the driver.
  4. For example, in Hall speed mode, switch hall-1 and hall-3 on the drive, and then switch motor-a and motor-b.

Reason: when the encoder speed feedback, the encoder power supply loses power.

Treatment: check and connect 5V encoder power supply. Make sure that the power supply can provide enough current. If using an external power supply, make sure that the voltage is to the driver signal ground.


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

Reason: motor in one or more directions is forbidden to operate.

Treatment: check the + inhibit and – inhibit ports.

Reason: the command signal is not grounded to the driver signal.


 After power on, the LED light of the driver is not on

Reason: the power supply voltage is too low, less than the minimum voltage requirement.

Treatment: check and increase the supply voltage.


Solutions to interference problems

1) Install power filter to reduce the pollution of AC power supply.

2) . one point grounding principle. Connect the ground of power filter, PE (ground) of driver (insulation between servo driver and chassis bottom plate), outgoing line of control pulse and direction pulse dir after short circuit, motor ground wire, cable protective sleeve between driver and motor, and shield wire of driver to grounding post on chassis wall, and ensure good contact.

3) Try to increase the distance between the control line, power line and motor drive line to avoid crossing. For example, when we deal with the installation position of two servo drives in the same chassis in the dual axis drive system, one driver's name plate is facing forward, the other is facing backward, and the structural arrangement should make these leads as short as possible.

Use shielded wire to reduce the interference from the outside world or from the outside world.