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Power down the machine completely. Inspect all orange fiber optic cables connecting the control unit's FSSB interface (typically labeled FSA/FSB on control board) through each amplifier in daisy-chain configuration. Check for visible damage, excessive bending (minimum bend radius 30mm), or disconnected connectors.

Never look directly into fiber optic cable ends - laser light can damage eyes. Always power down before handling fiber cables.

Clean all fiber optic connector ends using proper fiber cleaning swabs and isopropyl alcohol. Remove dust caps, clean both male and female connectors, and firmly reseat all connections. Ensure audible click when connecting.

Power up the control unit and observe amplifier LEDs. All amplifiers should show steady green FSSB LED (or LED labeled as 'FSSB READY'). If any amplifier shows red or no FSSB LED, that segment has communication failure. Replace fiber cables one segment at a time starting from control to first amplifier.

Navigate to SYSTEM > DIAGNOSIS > FSSB screen (or MAINTENANCE > FSSB STATUS depending on series). Verify all configured axes show 'NORMAL' or 'OK' status. Check which axis number is missing or shows 'ERROR' to identify the specific amplifier with communication loss.

Check the rotary address switches (typically labeled A1/A2) on each αi/βi amplifier front panel. Standard configuration: First axis=1, second=2, etc. Record all physical addresses and verify no duplicates exist in the FSSB chain.

Do not change rotary switches while power is applied to amplifiers.

Navigate to SYSTEM > PARAMETER and verify parameters 8000-8007 (Serial Spindle/Servo Channel Assignment). For standard configuration, parameter 8000=#1, 8001=#2, 8002=#3, etc. Ensure parameter values match the physical rotary switch settings on each amplifier.

Check parameter 8900-8907 (FSSB Axis Type) to ensure correct amplifier type is specified: 0=not used, 1=serial servo, 2=serial spindle. Mismatch between parameter setting and actual amplifier type will cause communication errors.

After any parameter changes, perform a full power cycle (CNC and amplifiers off for 30 seconds). Monitor FSSB DIAGNOSIS screen during startup to confirm all axes initialize properly and FSSB connection count matches expected number of amplifiers.

Parameter changes require CNC restart. Backup parameters before modification.

With power on, observe the FSSB READY LED on the CNC control board (near FSA/FSB fiber connectors). If this LED is off or red, the control unit's FSSB interface has failed. If green, the control side is functional and the fault is downstream in amplifiers.

Check DC link voltage and power supply LEDs on all amplifiers. Amplifiers require stable +24VDC control power and proper DC bus voltage (LED indicators on front panel). Low voltage or PS ALARM will prevent FSSB communication. Verify no other amplifier alarms are present on the LED display.