Diagnosing a Fanuc High Current Alarm 8,9, A, B or 12 on Fanuc Spindle and Servo Motors

Step 1

Disconnect the four motor leads from the drive.

Step 2

Power up and see if you have the HC alarm LED lit.

(Alarm can be HC LED, Alarm 8/9/A/b (Servo), or ALARM 12 (Spindle)

Step 3

If you no longer get the HC alarm, then your motor is probably bad.  Note:  Spindle HC alarms will not show up until you try to move the motor with a very low speed M command.

Step 4

If you still have the HC ALARM, then your drive is probably bad. However, we this process will not identify why the drive failed.

Step 1

With an ohm meter, check for shorts in the motor by measuring leg-to-leg and leg-to-ground on all three legs.

Leg-to-leg readings should be low, but consistent, on all three legs. The leg-to-ground readings should be open, or OL, on all three legs-to-ground.

Step 2

With a megger, check each leg-to-ground. The reading should show infinity (or 500 MEG and above) at the 1000V setting.

Check all three legs-to-ground because the problem can be in the power plug/terminal box of the motor or the power cables going from the drive to the motor.