FANUC servo systems rely on continuous feedback from the pulse coder (encoder) to monitor position and speed. The feedback loop uses specific wave signals, traditionally labeled as phase A ( ) and phase B (

This is the most definitive diagnostic test on a multi-axis machine. The procedure is:

The alert will typically display as (or whichever specific axis is experiencing the fault, such as Y, Z, or 4th/5th axes).

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If internal hardware is damaged, DIY fixes are often impossible due to the precision required for encoder alignment. FANUC C-Series Servo Amplifier Alarm Code 6. (Dot)