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Power down the machine completely and verify all FSSB cable connections between CNC and each servo amplifier are fully seated and locked.

Ensure LOCK-DOWN power is OFF before touching any connections.

Inspect FSSB cables for visible damage, kinks, or worn shielding. Check both the fiber optic cables (if applicable) and the dedicated FSSB communication cables.

Verify FSSB cable routing is away from power cables and high-voltage sources to prevent electromagnetic interference.

If damage is suspected, replace FSSB cables with genuine FANUC cables of correct length and type, then power up and observe alarm status.

Use only FANUC-approved FSSB cables to ensure proper impedance and shielding.

Check the rotary address switches on each servo amplifier to ensure unique, sequential axis assignments match the CNC parameter settings (check parameters 8100-8199).

Document existing switch positions before making changes.

Observe amplifier LED indicators during power-up sequence. Identify any amplifier without proper LED response or showing error codes.

Temporarily disconnect amplifiers one at a time from the FSSB chain (starting from the last amplifier) and power up to isolate which amplifier is causing the initialization failure.

Label all connections before disconnecting to ensure proper reconnection.

If a faulty amplifier is identified, swap with a known-good spare or replace. Verify all parameter settings match the replaced unit before full operation.

Ensure amplifier model and firmware version are compatible with existing system.

Access CNC diagnostic screens and check FSSB status display for any communication error codes or channel failures indicating controller-side issues.

Verify proper DC voltage supply to the FSSB interface circuit (typically 5V and 24V) using CNC power supply diagnostic pages or multimeter at test points.

Use proper ESD precautions when measuring voltages near control boards.

Reseat or inspect the FSSB interface card (if modular) or check main CPU board connections for corrosion or damage on connector pins.

Power down and wait 5 minutes for capacitor discharge before removing any boards.

If hardware failure is confirmed on the CNC side, contact FANUC service for board-level diagnostics or replacement of the FSSB master interface board.

Board replacement requires parameter backup and may need factory recalibration.