Fagor alarm 4157: ERROR 811: Defective Feedback2 encoder (direct/second feedback)
CNC 8055 SERCOS drive error (DDS) · Fagor DDS drives
What it means
The direct (linear-scale) feedback on X3 fails integrity checks - position loop reference itself is untrustworthy.
Likely causes
- linear scale reader head failing (LED aging, CCD degradation)
- scale cable damaged along the traveling chain
- contamination lifting signal amplitude below threshold
Triage note: Compare PV190 (direct) vs PV188 (motor) position at standstill - a slowly drifting delta condemns the scale head even if the alarm is intermittent. NOTE: 'S100/S120' are not valid Fagor scale types; Fagor linear scales are S/SV (legacy), S2/SV2 (current), LA/SA/GA (absolute).
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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SX-520 (legacy S) / SV2X-420-5-B (current)
Linear scale with integral scanning head · Primary suspect
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EC-P-D
Scale-to-drive feedback cable · Common cause
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LA-840
Absolute steel-tape scale (upgrade path) · Check if others ruled out
Need the part urgently?
Send us alarm 4157 with your machine details — typical RFQ turnaround is 24–48h.