A vertical machining center with Fanuc 6M CNC control system and DCI0 type PWM DC speed control units shows ALM401 alarm when turn on the power.

Check the speed control unit then found there was HCAL alarm light on of the Y axis servo driver, this means Y axis is overcurrent.

Take off the armature cable of the servo motor, and set S23 terminal as short circuit(this ensure no TGLS alarm due to armature cable is disconnected), re-start the power, the HCAL alarm is gone, so the problem is nothing to do with the driver, should be from armature cable or the servo motor.

Take off the Y axis servo motor, it was installed not in good position which caused coolant water come into the armature plug and shorted it, this is the problem.

Change the plug and take care of the coolant water protection, the machine resumed.