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Siemens SINUMERIK Controller
Safety · Intermediate · 30-120 minutes
Siemens 300744 - Axis drive safety monitoring checksum invalid, confirmation and
Alarm 300744 indicates a mismatch between the actual safety-relevant machine data checksum (MD 1398: $MD_SAFE_ACT_CHECKSUM) calculated by the drive and the reference checksum (MD 1399: $MD_SAFE_DES_CHECKSUM) stored during last machine acceptance. This safety monitoring mechanism detects unauthorized or corrupted modifications to safety-critical parameters in the SINUMERIK 840D control system.
300744
Siemens 300744 - Axis drive safety monitoring checksum invalid, confirmation and
Axis drive safety monitoring checksum invalid, confirmation and
The actual checksum of the safety-relevant MDs calculated by the drive and stored in MD 1398: $MD_SAFE_ACT_CHECKSUM (display of the checksum of the machine data for safe functions) has another value than the setpoint checksum stored during the last machine acceptance in MD 1399: $MD_SAFE_DES_CHECKSUM (checksum of the machine data for safe functions). The safetyrelevant data have been modified or there is an error. Request: During boot-up of the control Control reaction: Mode group not ready. Channel not ready. NC Start disable in this channel. Interface signals are set. Alarm display. NC Stop on alarm.
Root Cause Summary
Alarm 300744 indicates a mismatch between the actual safety-relevant machine data checksum (MD 1398: $MD_SAFE_ACT_CHECKSUM) calculated by the drive and the reference checksum (MD 1399: $MD_SAFE_DES_CHECKSUM) stored during last machine acceptance. This safety monitoring mechanism detects unauthorized or corrupted modifications to safety-critical parameters in the SINUMERIK 840D control system.
Safety
- Drive/power/encoder circuit: hazardous voltages may remain in the DC link after power-off. Lock out / tag out, wait for discharge per the drive documentation, and use qualified personnel only.
Causes and Fixes
- 1
Access Diagnostics > Machine Data on the control panel or use SINUMERIK Operate HMI. Navigate to MDs 1398 and 1399 to compare actual vs. desired checksums.
Do not modify these checksums directly; they are read-only safety parameters.
- 2
Review recent changes to safety-relevant MDs (e.g., MD 30402: SLS_LIMIT, MD 30406: SSL_LIMIT, MD 32010-32019 for axis safety). Check audit logs or machine history if available.
- 3
Restore the safe machine data to the last known good backup and perform machine acceptance (Commissioning > Safety > Accept Changes) to regenerate MD 1399 checksum.
Only authorized commissioning personnel should perform acceptance; this typically requires Siemens commissioning software or 840D engineering mode.
- 4
Power-cycle the drive or issue a POWER ON reset via NCK control to reinitialize safety monitoring and verify checksum alignment.
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