Diagnose a Fanuc High Current Alarm in 10-Steps

Step 1

Access the electronics cabinet with the power on (WARNING: Hazardous voltage inside).

Step 2

Look for the amplifier unit displaying either Fanuc servo alarm 8, 9, or A on the seven segment display.

Step 3

Alarm 8, 9, and A are all the same problem. However, the different alarms identify which amplifier axis the alarm exists on.

Step 4

Turn on the main breaker of the machine and leave the CNC off.

If Fanuc servo alarm 8, 9, or A appears when the CNC is off, disconnect the feedback connector to the amplifier axis indicated by the alarm and turn on the main breaker with the CNC off again.

If no alarm appears, there is an issue with the feedback cable or the pulse coder.

If alarm 8, 9, or A appears with the feedback cable disconnected, the amplifier is most likely faulty and needs to be replaced.

If the alarm ONLY appears when the CNC is turned on, you need to troubleshoot the drive, motor, and power cable.

Step 5

Disconnect the four motor leads from the bottom of the amplifier.

Step 6

Turn on the CNC and release any emergency stop condition (if you’re removing the motor power with a vertical axis, physically prop up the axis or else it will fall when the emergency stop and servo motor brakes are released).

Step 7

If an alarm 8, 9, or A still appears, the drive is probably faulty and needs to be replaced.

Step 8

If an alarm doesn’t appear, the motor and/or power cable may be faulty and needs to be diagnosed.

Step 9

With an ohm meter, check for shorts in the motor by measuring leg-to-leg and leg-to-ground on all three legs. An ohmmeter will tell you if your motor is shorted. Leg-to-leg readings should be low, but consistent, on all three legs. The leg-to-ground readings should be open (OL) on all three legs-to-ground.

Step 10

With a megger, check each leg-to-ground. A megger will tell you if your motor is grounded. 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.