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Power down the machine completely and lock out electrical power per safety procedures.

Always follow LOTO procedures. Capacitors in amplifiers remain charged after power-off.

Inspect all FSSB cable connections from the CNC through each amplifier in the daisy chain. Check for bent pins, loose connectors, or visible cable damage.

Disconnect and reconnect each FSSB connector firmly, ensuring positive latching. Pay special attention to the amplifier identified in the alarm detail if a specific slave number is shown.

Power up the system and monitor for alarm recurrence. Check diagnostic screen for FSSB slave status to verify all amplifiers are communicating.

Identify which slave amplifier is faulting by checking the alarm detail or diagnostic parameter screen (typically shows slave axis number or amplifier position).

Check for LED indicators on the suspect amplifier. No power LEDs or abnormal LED patterns indicate amplifier failure. Note any additional alarms on the amplifier display.

Temporarily bypass the suspect amplifier in the FSSB chain by connecting the FSSB cable from the previous device directly to the next device. Power up and check if alarm clears.

Machine will not operate the bypassed axis. This is for diagnostic purposes only to isolate the failed component.

If bypassing clears the alarm, replace the failed amplifier or FSSB communication board. Restore proper FSSB chain routing and verify all axes communicate properly.

Verify FSSB cables are routed away from power cables, inverters, and high-voltage sources. Maintain at least 6 inches separation where possible.

Check that FSSB termination resistor is installed on the last amplifier in the chain. Verify termination switch setting matches Fanuc documentation for your amplifier series.

Measure total FSSB cable length in the chain. Ensure it does not exceed maximum specification (typically 50m total for most systems). Replace any suspect cables with known-good FSSB cables.

Check for proper grounding of all amplifiers and the control cabinet. Verify shield connections on FSSB cables are intact and properly terminated at both ends.