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Power down the machine and visually inspect all FSSB cables between the CNC and servo amplifiers for physical damage, kinks, or excessive bending near connectors.

Always follow lockout/tagout procedures before opening electrical cabinets.

Disconnect and reconnect all FSSB connectors at both the CNC control side and amplifier side, checking for bent pins, debris, or corrosion. Clean connectors with electronic contact cleaner if needed.

Check cable routing to ensure FSSB cables are not running parallel to power cables or in areas with high electromagnetic interference. Maintain at least 6 inches separation from AC power lines.

If damage is found, replace the FSSB cable with a genuine Fanuc cable of the correct length and type. Test communication after replacement.

Never use non-Fanuc cables or extend FSSB cables beyond manufacturer specifications.

Check all servo amplifier status LEDs. Identify any amplifiers showing error states (red LEDs) or no power indication (no LEDs). Document which axis amplifiers show abnormal status.

Verify that all servo amplifiers have proper DC bus voltage (typically 280-320VDC for αi series). Check the power supply unit and measure voltage at each amplifier's DC bus terminals.

Use proper PPE and insulated test equipment when measuring high voltage DC bus.

Access the servo diagnostic screen on the CNC (SYSTEM > SERVO > FSSB STATUS) to identify which axis or amplifier address is dropping off the bus or not responding.

If a specific amplifier is identified as faulty, swap it with a known good amplifier of the same model or replace with new unit. Re-establish FSSB communication and verify all axes appear in the diagnostic screen.

After replacing an amplifier, axis parameters may need to be reloaded and the system may require re-homing.

Verify that the FSSB terminator is installed on the last servo amplifier in the chain. Check that the termination switch or resistor is properly set according to the amplifier documentation.

Check CNC parameter 8100-8107 (FSSB configuration parameters) to verify the number of axes and FSSB addresses match the physical installation. Compare with machine documentation.

Do not modify these parameters without proper documentation and backup. Incorrect settings can prevent the system from booting.

Verify each servo amplifier has a unique axis address set correctly via rotary switches or software configuration. Check for duplicate addresses in the chain.

If parameters were recently changed or after a battery replacement, reload the original CNC parameters from backup. Initialize the FSSB by cycling power to the entire system (CNC and amplifiers together).

Parameter restoration may reset all machine settings. Ensure you have a verified backup before proceeding.