SP9004 (Alarm 04) Input Fuse / Voltage Low (Spindle) fault in Fanuc drive

SP9004 (Alarm 04) Input Fuse / Voltage Low (Spindle) fault in Fanuc drive

Description

SP9004 (Alarm 04) is a Spindle Amplifier specific power alarm. It indicates that the AC input voltage powering the spindle drive is missing a phase or is significantly undervoltage. On many Alpha-series spindle drives, the unit detects the input waveform. If one phase is missing ("Single Phasing"), the ripple on the DC bus becomes dangerous. Alarm 04 protects the input rectifier bridge from burning out due to uneven loading.

Cause

• Open Phase: A blown fuse in the main disconnect or a tripped breaker on one leg of the 3-phase supply.
• Contactor Failure: The Magnetic Contactor (MCC) supplying the drive has burnt contacts on one pole.
• Input Board Failure: The circuit on the spindle drive PCB that detects the AC waveform has failed.

Solution

1. Live Measurement: Carefully measure the AC voltage at the input terminals of the Spindle Drive (usually labeled L1, L2, L3) while the machine is powered on. You must see balanced voltage (e.g., 200V, 200V, 200V).
2. Check Upstream: If one leg is 0V, trace back to the main breaker, noise filter, or reactor.
3. Check Ribbon Cable: Ensure the ribbon cable connecting the power section to the control card is seated, as the sensing signal often travels through it.