Fagor alarm 4028: The light does not reach the CNC through the optic fiber
CNC 8055 SERCOS drive error (DDS) · Fagor DDS drives
What it means
At power-up the transmitted SERCOS light never returns to the CNC receiver - the ring is optically broken.
Likely causes
- fiber not seated in optical module (dust in bore)
- fiber crushed in cable tray or snapped at the strain relief
- a drive in the ring completely dead (no re-transmission)
Triage note: Cheap test: short-wave the fiber at the CNC IN port - if a flashlight beam reaches it, path exists; then bisect the ring drive-by-drive.
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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DDS fiber-optic ring cable (cut to loop length)
SERCOS fiber-optic cable assembly · Primary suspect
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AXD/SPD module showing blank display
Dead drive breaking re-transmission · Common cause
Need the part urgently?
Send us alarm 4028 with your machine details — typical RFQ turnaround is 24–48h.