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How to troubleshoot a Unity ERIO Hot Standby system at start up.

A good starting point is to eliminate the essential hardware as the source of the problem. Work with the minimum required modules. In each PLC backplane, only use the PS, CPU and CRP. Set up a single ERIO CRA drop that only includes the PS and CRA in the backplane(a drop is required).
Make the following connections:
1: HSBY Link between the two CPUs.
2: CRP(a) ETH3 to CRP(b) ETH3
3. CRP(a) ETH4 to CRA ETH2
4. CRP(b) ETH4 to CRA ETH3

These are the minimum connections and hardware required for a Unity Quantum ERIO Hot Standby system. After setting up and connecting all of the above hardware, only power up a single CPU and the CRA backplane. Load the program into the CPU and it should come up in Primary mode when placed into Run. You can test both sides independently to make sure that they come up Run Primary. If they come up as Run Primary independently, leave the Primary powered up and then power up the other PLC while Holding the ESC key. Release the key after the erasing RAM message appears and at the end, it should come up as RUN Standby.

As I said, this is a good starting point, if it comes up in Run Primary and Run Standby, you can then start adding your additional hardware and switches.

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