Solution of the servo drive receives no pulses

Fault Name: 

The servo drive receives no pulses.

Fault Symptom:

When the PLC sends a pulse to the drive, the drive cannot run and no fault is reported.


The drive reports that the input optocoupler has been damaged due to the unstable voltage 24V.


First ensure that the wiring is correct, then monitor 19. CP has no value change, indicating that the drive cannot receive and transmit the pulse signal, so the drive is damaged.


Generally, when the PLC sends the number of drive pulses, it will be displayed in 19.CP. If there is no value display, it means that: 

The pulse line CN1 connected PLC and drive is disconnected or the wiring is incorrect. 

The driver's high-speed optocoupler is partially damaged.

Test method (take SD600A as an example): If the maintenance room has no PLC or high-speed pulse device, colleagues do not have a motor either, you can test the high-speed port with the connection method 2 of the manual.

1.NPN connection test: Connect CN1-35(PL1) to +24V and connect pulse signal 41(/PULSE) to OV(0V of 24V), monitor 19.CP if there is any change in value, if there is change in value indicating that the high speed optocoupler part of the pulse is not damaged. If not, the high speed optocoupler is damaged. Then connect 37(/SIGN) directly to 0V, and click 41(/PULSE) again to use 0V to see if the data is decreasing on the original basis. If the value increases or decreases in the opposite direction of the original, it indicates directional optocoupler is not damaged. If it is still increasing as the same as the original, it indicates it’s damaged.

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