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Power down the machine completely and verify all FSSB cable connections at the CNC, each amplifier, and terminator are fully seated and locked.

Ensure proper lockout/tagout procedures before accessing electrical panels.

Inspect FSSB connectors for bent pins, corrosion, debris, or physical damage. Clean contacts with approved electronic contact cleaner if contamination is present.

Check FSSB cable routing for sharp bends (minimum bend radius 10x cable diameter), pinch points, or proximity to power cables or noise sources. Re-route if necessary.

If available, swap suspect FSSB cable with known good cable or swap cable positions between amplifiers to isolate faulty cable. Replace any damaged cables with Fanuc-approved FSSB cables only.

Never use non-Fanuc cables on FSSB networks as impedance mismatches will cause data errors.

Verify cabinet ground connections are tight and measure resistance from cabinet frame to machine ground (should be less than 0.1 ohms).

Check that FSSB cable shields are properly grounded at both ends through the connectors. Inspect for broken shield connections or improper cable termination.

Identify any new equipment installed near the CNC or recent changes to facility power. Check for nearby VFDs, welders, or other high-noise devices without proper filtering.

Install or verify ferrite cores on FSSB cables if operating in high-EMI environments. Ensure minimum 12-inch separation between FSSB cables and power cables.

Access servo diagnostics and identify which amplifier position on the FSSB chain is reporting the error (check FSSB connection number in detailed alarm history or LED status).

Swap the suspect amplifier's position in the FSSB daisy-chain with another amplifier. If the alarm follows the amplifier, replace it. If alarm stays with the position, suspect cable or CNC board.

Power down and follow proper amplifier handling procedures. Note original axis assignments before swapping.

Check amplifier LED indicators for fault codes. Verify amplifier cooling fans are operational and heatsinks are not excessively hot (clean any dust buildup).

If all cables and amplifiers test good, suspect CNC axis control card FSSB interface. Contact Fanuc service for board-level diagnostics or replacement of the servo control board.

CNC board replacement requires parameter backup and restoration by qualified personnel.