Siemens alarm 25020: Axis %1 zero mark monitoring of active encoder

What it means

The plausibility check between zero-mark pulses of the active position encoder failed: pulse counts between successive zero marks differed beyond tolerance, usually due to transmission disturbance or encoder electronics faults. Axes of the channel must be re-referenced after clearing.

Likely causes

• Damaged/noisy encoder cable or loose connectors
• Encoder supply outside tolerance
• Faulty encoder evaluation electronics
• Mismatch between MD34220 $MA_ENC_ABS_TURNS_MODULO and SINAMICS parameter P0979

Replacement parts

We supply the following units for this alarm — tested, warranty-backed:

• position feedback encoder per axis spare list

  encoder · Check if others ruled out

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