A machine operator reported that his production process increasingly suffered from spindle failures. The spindle tried to start, produced a deep humming noise and aborted after a few seconds with alarm 31, shortly followed by 9031. The L and M axes were unaffected, which helped narrow down the failure. The amplifier was sent to our workshop for full testing.

Before opening the device, a complete inspection and electrical test were performed. When connected to our Fanuc test system, the amplifier reproduced the exact behaviour described by the customer. At 100 rpm, the motor hesitated, oscillated and drew uneven current. After three to four seconds, the current protection shut the system down. This confirmed that the issue was within the amplifier power stage.

The detailed analysis focused on the IGBT output stage. Measuring the phase currents revealed that one phase carried significantly more load than the others. This asymmetry is a classic pattern for a partially failing gate driver or IGBT cell. The thermal marks on the board supported this conclusion. The entire power stage was removed and tested individually. Under low speed switching, the suspect IGBT exhibited unstable switching behaviour.

The repair involved replacing the entire power stage, refurbishing the control board and verifying the gate drive circuits. All connectors were cleaned, thermal compound renewed and the cooling channels flushed. A complete electrical cleaning and diagnostic sweep followed.

After reassembly, the amplifier was reconnected to our Fanuc test bench. The spindle now started smoothly at 50 rpm. No humming, no vibration, no overshoot. After that the amplifier was tested under full load and heat. Several hours of continuous stress were performed to ensure long term stability.

The module passed all tests and was released with full documentation. The customer confirmed stable operation since reinstalling the repaired unit.

Preventive Measures

• Replace fans regularly
• Clean heatsink and airflow channels
• Inspect motor connectors
• Check insulation values periodically
• Document parameters

Conclusion

With systematic diagnostics and a realistic test bench, Fanuc spindle amplifiers can be repaired reliably and sustainably.

To mentioned Fanuc Drive: Fanuc A06B-6134-H203#A Spindle- Servo Drive Unit

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Fanuc drive Repair by Industrypart

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Device Description

Operating Environment and Compatible Devices

This spindle amplifier is used in Fanuc controlled CNC machines such as lathes, machining centers and automation systems. It drives the spindle as well as L and M auxiliary axes. Compatible with Fanuc αi spindle motors and Fanuc CNC systems like 0i-MD, 31i-A, 32i-B.

Functional Description

The amplifier converts incoming AC power into a regulated DC link and drives the spindle and axes through high speed IGBT switching. It manages torque, speed and feedback signals. Protection logic monitors current, DC bus voltage, motor temperature and communication.

Alarm Messages and Troubleshooting

Components