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

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.

By measuring through the four disconnected motor leads, you can check the power cables and the motor at the same time.

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.

An OHM Meter will tell you if your motor is shorted.

A Megger is required to see if your motor is grounded.

Get your machine back up and running.

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