Fagor alarm 4115: ERROR 804: Defective encoder (motor feedback)
CNC 8055 SERCOS drive error (DDS) · Fagor DDS drives
What it means
Drive communicates with the rotor feedback but its signals fail integrity checks - encoder electronics degrading.
Likely causes
- integral FXM/FKM sinusoidal encoder failing (bearing-current damage typical)
- chronic cable shield breaks corrupting differential signals
- X4 CAPMOTOR board input stage damaged
Triage note: Rule out the cable first (swap with a known-good axis). Encoder memory holds the motor sales reference - a replacement FXM lets the drive auto-identify via MP1.
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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FXM78.20A (match installed model)
FXM servo motor (integral feedback) · Primary suspect
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IECD-x
TTL incremental feedback cable · Common cause
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AXD 1.25 (module with faulty X4)
Drive module (board-level repair) · Check if others ruled out
Need the part urgently?
Send us alarm 4115 with your machine details — typical RFQ turnaround is 24–48h.