Siemens S7-1500 OB86 rack failure for ET 200SP
What causes an intermittent OB86 rack failure for an ET 200SP station on a Siemens S7-1500 PLC?
An intermittent OB86 rack failure on a Siemens S7-1500 for an ET 200SP station, where the machine continues to run, suggests a temporary issue with the station's connection or power. The fault clears itself after a few hours.
Likely causes and checks
1Intermittent Network Interruption
- Points to it
- The repeated failure and return of the OB86 event points to an intermittent network problem rather than a dead device.
- Check
- Check the cabling, connectors, and switch ports on the path to the ET 200SP device. Read the PROFINET port diagnostics for the affected station and export the diagnostics buffer to check for Fault_ID 16#CB associated with the OB86 events.
2Intermittent Device Power Loss
- Points to it
- An intermittent loss of 24V supply to the ET 200SP station could cause it to drop off the network and then return when power is restored.
- Check
- Check the ET 200SP station's 24 V supply and its protection (e.g., circuit breaker, fuse) for intermittent issues. Look for device LEDs turning off when the fault occurs and export the diagnostics buffer to see if the device failure coincides with any supply events.
Next check: If the above checks do not resolve the issue, compare the device name, IP address, and configured modules of the ET 200SP station with the project configuration in TIA Portal and check the diagnostics buffer for Fault_ID 16#CD or 16#CE, although this is less likely for an intermittent, self-recovering fault.
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