SF fault in S-7 300 PLC

Hello Kalokhe;

Your first reflex should be to connect your programming software (Step 7 or TIA Portal) to your CPU and to open the diagnostic buffer of your PLC.

This buffer contains a list of all events that have recently happened on the CPU, and should give you hints on what the PLC is complaining about.

Reaction to problems registered in the diagnostic buffer use diagnostic OBs (search in the online help for more details), These OBs interrupt the diagnostic cycle and allow operations of the CPU in case of specific events, while completing the information in the diagnostic buffer. If you see entries in the diagnostic buffer such as "Missing or inaccessible OB: OBxxx" then create and download an OB of that number (replace xxx by the actual number), without internal programming. This by itself should helpprovide more information onthe sources ofthe error that is bothering your CPU.

If entries in the diagnostic buffer are not clear, save the ("As Text") and attach them to your reply so we may help you understand them.

Hope this helps,

Daniel Chartier

Note:

I have added Chapter 23 "Diagnostics" from the S7 Programming manual, it explains the diagnostic buffer and the diagnostic OBs in great detail, along with othe diagnostic functions available to the user. D.C.