Troubleshoot Fanuc Alarm 8, 9, A
Getting FANUC Alarm 8, 9, or A? It's high current—here's the fix.
Getting FANUC Alarm 8, 9, or A? It's high current—here's the fix.
Alarms 8, 9, or A indicate high current or a short circuit in the servo amplifier or motor. Each code corresponds to an axis:
• 8 = L Axis
• 9 = M Axis
• A = N Axis
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Does the alarm occur before motor power is applied?
Yes: You have an issue with the feedback or the servo amplifier.
Disconnect the feedback cable and power on. If no alarm, the problem is the feedback cable or pulse coder. If the alarm is there, the servo amp is the cause.
No: Continue troubleshooting with the steps below 👇
Does the alarm occur after motor power is applied?
Yes: You have an issue with the motor power or the servo amplifier.
Disconnect the motor power cable and power on. The problem is the servo motor or motor power cable if there is no alarm. Confirm the motor is the issue by completing the Servo Motor Static Test.
If the alarm remains, the servo amp is the problem. Confirm the servo amplifier is the issue by completing the Servo Amplifier Static Test.
IMPORTANT: Shut off Power Check the outputs by using a Huntron Tracker or an Ohmmeter. If readings vary, replace or repair the servo amp.
Measure the resistance from the positive bus bar to the motor power connectors U, V, and W terminals. You will be looking for high resistance (hundreds of kΩ and up), and the measurements should be similar between the three terminals.
Next, measure the resistance from the negative bus bar to the motor power connector U, V, and W terminals. You will be looking for high resistance (tens of kΩ and up), and the measurements should be similar between the three terminals.
IMPORTANT: Shut off Power Disconnect the power cable from the servo amplifier. Grab your megohmmeter and measure the insulation resistance from the disconnected motor power leads to ground. You can purchase a low-cost model for around $100. We recommend the Supco M500 for its ease of use.
If a grounded condition is detected, separate the motor and motor power cable and re-test. Still grounded? Then you most likely have a bad cable. Otherwise, you have a good cable with a bad motor. You will need to repair or replace the servo motor.
Use the Resistance Value Chart to determine the severity of the grounded condition.
| Insulation Resistance | Status | Recommendation |
|---|---|---|
| 400 MΩ or higher | Good | Safe to use |
| 150 to 300 MΩ | OK | May fault under load or heat |
| 40 to 100 MΩ | Caution | May damage other equipment |
| 20 MΩ or lower | Bad | Do not use |
Engineer Tip: Motors can also fail phase-to-phase. Use a multimeter to check the motor winding resistance between phases. The motor is bad if the resistance is not equal phase to phase.
If resistance checks out, the fault is likely inside the amplifier (opto-isolators, current sensors, or IGBTs). Replace or send it to a qualified repair center. Don't install a new amp until you've confirmed the motor and cables are good.