PM866 switching from Upper to Lower back and forth with no reason
We are running redundant pair of PM866. When both PM866 are up and running, we are experiencing strange behaviour. In control builder the primary controller is for about 15-20 seconds the "lower/secondary" PLC, then it switches with no reason to "Upper/Primary" for few seconds and we loose all cards and it goes back to "lower/secondary" PLC and works again with no issues. This keeps going over and over.
The LED diods on both PLCs do not report any fault. If we switch off the toublemaker Upper/Primary, than everything is fine.
PS: please note we are working remotely due to the covid situation and have no physical access to the controllers.
Any idea what can be wrong?
So it switches from the Lower to the Upper all by itself for a few seconds, without any input to switchover? Weird. Sounds like an RCUBackup problem on the Upper, but that still doesn't explain why it would try to take over as Primary intermittently, unless there's also a problem with the lower.
Do you know if you lose all the IO and it goes to ISP/OSP, or just that the you can't see the IO when it's on the Upper? I ask because it's possible that the Upper can still see the ProfiNET IO, but just you can't, if you can't see your Controller on the Control Network. Can you view the ProfiNET IO? Maybe enable the CI871 Web Server to see?