Rx7i DROPOUT

I have an Rx7i that is dropping out randomly. The modules and rack have been replaced. The CRM is on one of the I/O modules (rack 1 slot 6) so when it drops out, the machine is down and I can't monitor status anymore. Using only 1 module (for the CRM) it drops out 1hr or 2hrs or 15mins after reset. I am hoping to find a method to monitor voltage, current or comm's signal to zero-in on the culprit. Can anyone offer some tips on past experience. I don''t believe in gremlins, even though we are near Halloween. There is an extension rack with 3 modules on it, but I have reduced this to the main full rack. Thanks Jim .

Are there any entries in the PLC's fault tables?

My bad...I have added three pix for review

Anything in the Controller faults table? It appears that the CPU is losing contact with expansion rack #1. What is in it?

Solved

FYI...We ended up replacing the terminator on the extension rack. The only thing we had not swapped. It was warm when we took it off. Don't know if the coolant or oil got to it, but the new has it up and running. I would have expected a fault to appear for that.but alas, the older I get the less expectations are met.

Thanks to all. Jim