S7-300 Faults

[maharshicool]

Hi all

I have been having trouble solving the faults on the CPU. All the leds SF,BF,DC5V,FRCE,RUN,STOP start blinking on the 314C-2DP and after reset or by switching off the panel and then switching ON the faults vanishes. I have 5 CPU connected on MPI and exchanging data. I have changed the profibus cable, all the connector to that CPU but no change in status. The fault would happen maybe once or twice in a day.

I need help

 

[JesperMP]

Hej maharshicool.

Whenever the fault has just happened, go online with STEP7 and investigate the diagnostics buffer.

Anyway, I have a hunch that the problem has to do with the MPI network.
MPI is really not very good for connecting many PLCs together. For one PLC and one local HMI it is OK, plus maybe a PG occasionally.
The problem is that the MPI bus is not isolated to the backplane of the CPU. So all your CPUs share the same potential when connecting with MPI. A scary thought.
For this reason, it is recommended to limit the complete MPI network to max 50 meters. With 5 CPUs it soon becomes difficult to stay within this limit.
Another thing to look out for is to have a VERY GOOD common ground for all the connected machines and CPUs.