You can try for test. Take IM151-3 module from other non working cabinet to first cabinet Connect profibus cable and power to this other IM151-3 module (don't forget end resistor of IM151-3) Dont't change any slave dips and don't connect any IO-cards to IM-module.
If CPU detects this other IM151 module, but says faulty (as there is no configured IO cards connected) then problem is on cabling (or in first cabinets profibus connector outlet) after first working cabinet.
If it still says that for IM151-3 no available then there is other error.
Just wanted to respond back to this. We did this and it helped us narrow the problem down and eventually fix it. Thank you very much!
It's funny because I do things like this to troubleshoot all the time, but I think getting used to new software and protocols and processes threw me off my usual track.
So the electrician had replaced the Profibus cable between 1 and 2 and had replaced the connector at 2. What we found was yes, the IN side of 1 worked, but the OUT side did not. They didn't have any more connectors on-site so what we ended up doing was swapping connectors with 1 and 6, since 6 was the end of the line and didn't need an out.
We got everything coming in and talking!
Thanks a ton for everybody's advice on this! I really appreciate it.