Troubleshoot Open Armature Circuit (G3 CNC)

First check the thermal overloads:
On the earliest G3 CNC's, shipped before 2007, these are accessible through a finger-hole on the side of the blue cover; after about mid 2007, these are on the back panel.

When you press the tripped overload you should feel a distinct click as it resets. If it feels soft, or doesn't fully engage, the thermal overload may be bad.

If one axis doesn’t move, but it throws a servo-error in Jog-2 or Jog-3 (in Jog-1 you can see the position counter changing), the motor might be bad, or the motor armature circuit might be open.

To quickly determine if the motor is bad:
(For this example, assume the Z-axis is bad)

• Set servos off, disconnect both motor cables at back of control, and connect the bad axis motor cable (Z in this example) to the good axis (X in this example).
• Jog the good axis (X in this example)
• If you still get servo error, replace the motor.
• If the bad axis (Z) moves, the motor is good and the issue is in the control.

To troubleshoot the armature relay circuit and thermal overloads:
If the armature circuit is 'open', the motor terminals on the servo amp will be about the same as the bus voltage. Set servos off, reconnect motors and set servos on. Measure DC volts at motor terminals on the bad axis: if it is 60 to 70VDC, the armature circuit is open.

Examine the illustrations below:
NOTE: Before about 2007, chassis-mount thermal overloads were used; after 2007, the overloads were mounted on back panel. Refer to the appropriate illustration.:

• Tug on the red and black wires that go through the connect card; they should not pull out. (Check both axes to compare)
• With servos on, measure DC volts across the thermal overload; it should be near zero volts; if not, replace the overload. (Check both axes to compare)
• Measure across the armature relay contacts; voltage should be near zero volts; if not, replace the relay. (Check both axes to compare)