If switch on redundant controller immediately, it goes in fault mode
My plant is running without issue from last 4-5 years with PM862 redundant controllers.
Total load is 78% in running plant.
Suddenly standby controller goes in fault mode and when I switch off the faulty controller and wait for 5 or more minutes to switch on, it runs perfectly but if i switch off and on the controller then it again goes to fault mode.
Result is same for both controllers, either I make primary or secondary any controller. If I wait to switch on secondary then everything is fine but on immediately the controller goes in fault mode.
Otherwise both controllers are showing redundancy.
Voted best answer
In addition to the other answer - if assume HW is OK, in order to initiate a Warm restart, you need to power off the CPU for a few seconds, according to the manual.
What happens if you disconnect the power supply for 10 sec (instead of 5 min) or initiate restart backup CPU from Control Builder?
Also, connect a serial cable to the secondary CPU and listen via HyperTerminal or PuTTY tool. (Connect console cable to controller's COM4 and serial/usb to the node where HyperTerminal or PuTTY is running). What messages do you see?
Did you try changing the RCU cable?
Reconfirm tight connections of the controllers, modules and their cables.
What does the System Event List say during secondary's fault?