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Power down the machine completely and inspect all FSSB cable connections at both the CNC control and each servo amplifier. Verify connectors are fully seated and locking tabs engaged.

Always follow LOTO procedures before opening electrical cabinets.

Examine FSSB cables along their entire length for physical damage, pinching, excessive bending (minimum bend radius 10x cable diameter), or cable ties that are over-tightened.

Check cable routing to ensure FSSB cables are separated from power cables by at least 100mm and not bundled with AC power or motor cables which cause EMI.

If damage is suspected, swap the FSSB cable with a known good cable of identical specification. Use only genuine Fanuc FSSB cables as generic substitutes often lack proper shielding.

Check the alarm history and servo diagnostic screens (System > Servo > FSSB) to identify which specific axis amplifier is reporting the link error.

Inspect the identified amplifier for LED status indicators. Verify the power supply LEDs are solid and the FSSB communication LED shows normal activity (typically green and steady or blinking).

Power cycle only the affected amplifier by switching off its circuit breaker, waiting 30 seconds, then powering back on. Monitor if the alarm clears and the amplifier rejoins the FSSB network.

Note the amplifier position in the FSSB chain before disconnecting power.

If the alarm persists, swap the suspected amplifier with an identical unit from a working axis to isolate whether the fault is in the amplifier hardware or the FSSB network segment.

Ensure amplifier parameters match the axis assignment or re-configure after swapping.

Verify the FSSB termination resistor is installed at the last amplifier in the daisy chain. Check the connector for the terminator plug (typically a small connector cap marked 'TERM' or 'T').

Measure ground continuity between the CNC control cabinet ground bus and each servo amplifier chassis ground. All grounds should reference the same point with less than 1 ohm resistance.

Use a dedicated grounding point; avoid daisy-chaining grounds.

Inspect cable shield grounding at both ends. FSSB cable shields should be grounded at the control end only to prevent ground loops, with the amplifier end shield insulated and not touching chassis.

Check parameter setting for FSSB configuration (parameter 8000 series). Verify the number of configured axes matches physical amplifiers and the FSSB speed setting matches all amplifier capabilities.

Incorrect FSSB parameters can prevent proper network initialization.