allen bradley compactlogix

jmoats75

Member
Join Date
Aug 2012
Location
pittsburgh
Posts
4
Need help troubleshooting with compactlogix modules. Have fault on plc. contractor and engineering is saying cannot talk to modules slot 2 thru slot 9. Is there a way to figure out which module is bad without going through all 9 that are different types thanks in adavace
 
these questions are pretty basic – but we've got to start somewhere – and please remember that we can't see your system ...

so ...

are ALL of the little white "latches" on the tops of the modules pushed COMPLETELY ALL-THE-WAY to the left? ...

do you have an END-CAP installed on the right side of the system? ... this ABSOLUTELY MUST be installed to "terminate" the connection – or the system will NOT communicate with the modules ...

have you added all of the modules to the I/O Configuration area at the bottom of your project tree? (far left side of the screen) ...

and the most basic question: did the system work before – and now it won't work? ... or is this a NEW installation that has never worked at all? ...

Have fault on plc.

what does the fault window say? ...

remember – the more you details you give us, the more detailed we can make our answers ...

and welcome to the forum ...
 
Last edited:
this is an existing system that was working fine until friday. all white tabs are connected, end terimals are installed. from my understanding there is no communications from slot 3 through 9. they are able to communicated with the first two modules that are input modules but unable to communicate with the rest of the modules. the contractor recommendation was to start with slot 3 and start replacing module until the fault clears. However, I think there has to be a better way to troubleshoot to find the correct moddule that is given me problems. as well as I dont have all module in stock to do this type of shotgun approach to troubleshooting. How do I know I dont have more than one module bad from slot 3 through 9.
 
Yea all the common troubleshooting was done. Try one new input module yesterday with nlo help. Just would like to know is there a way to isolated which module or modules that are faulty. Anyway to check the bus for communication error
 
jmoats75 - I do not have a direct answer to your question, BUT I had much the same problem with one of my machines and while I am not 100% sure if this was the root cause or if the problem is truly gone, we did find that there was a problem with the Ethernet switch to which the PLC was connected. After replacing that switch, the problem has not resurfaced.

Steve
 
Yes. I was seeing the first module but none of the others after that. Like you, it had been working fine and then stopped working. One time, the problem went away for about two weeks and then came back again. I never found any problem with any modules. It's been about a 6 weeks since the Ethernet switch was replaced and I there have been no communications problems since.
 
I guess you COULD make a good backup of the current program, then start a new basic program that only uses 5 modules. You could then start leaving out one module at a time until the fault clears.

When you find which module it is, replace it, make sure they are in order, and download the original program back to it.
 

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