What causes Siemens SINUMERIK alarm 104121?

Parameter configuration error in the machine data for the affected axis or channel. Hardware fault on the axis drive or control module. Incorrect axis assignment or configuration in the SINUMERIK machine data. Software or firmware version incompatibility. Communication fault between NC and drive system.

How do I fix Siemens SINUMERIK alarm 104121?

1. Check the SINUMERIK alarm list for any sub-alarms or related alarms active at the same time. 2. Review the machine data parameters referenced in the alarm description for the affected axis. 3. Power cycle the machine to reset transient faults. 4. Check the SINAMICS drive diagnostics for the affected axis. 5. Consult the Siemens SINUMERIK alarm manual for alarm 104121 for detailed remedy instructions.

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Siemens SINUMERIK Controller

Spindle · Intermediate · 30-120 minutes

Alarm 104121

Siemens 840D 104121 - PA: Error on reading number of spindles

Alarm 104121 indicates a failure in the NCK parameter reading process for the number of spindles configured in the machine tool. This occurs during system initialization when the SINUMERIK 840D reads spindle configuration data from machine data (MD) parameters, typically MD20050 (Number of spindles). The alarm prevents NCK startup until the spindle configuration is correctly readable.

Siemens SINUMERIKSpindleIntermediate30-120 minutes

104121

Siemens 840D 104121 - PA: Error on reading number of spindles

PA: Error on reading number of spindles

Root Cause Summary

Alarm 104121 indicates a failure in the NCK parameter reading process for the number of spindles configured in the machine tool. This occurs during system initialization when the SINUMERIK 840D reads spindle configuration data from machine data (MD) parameters, typically MD20050 (Number of spindles). The alarm prevents NCK startup until the spindle configuration is correctly readable.

Safety

Refer to Siemens documentation
Ensure qualified technician performs repairs

Causes and Fixes

1
Access Siemens HMI menu: Diagnostic > Machine Data > Search for MD20050 (MM_NUM_SPINDLES). Verify the parameter exists and contains a valid value (typically 1-4 spindles).
Do not edit while machine is in RUN or AUTO mode.
2
If MD20050 is missing or shows value 0, enter the correct number of spindles configured on your machine tool. For single-spindle machines, set to 1. For multi-spindle machines, set accordingly.
Incorrect spindle count will cause subsequent spindle-related alarms during operation.
3
Save the machine data modification (HMI: Parameter > Save or use NCK backup/restore function). Perform a warm restart (CTRL+ALT+DEL on operator panel or power cycle if required).
4
Monitor NCK startup messages in Diagnostic > System Messages. If alarm 104121 clears, spindle configuration was the issue. If it persists, proceed to next cause.

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