S7-315DP Error

[Steve G 1]

I have a system with a PLC, two drives and a remote I/O rack attache to it. A few days ago the PLC faulted and had a SF light on and the BF light flashing. The last time this happened one of the power rail units that link the remote I/O to the PLC went bad. I ordered a new one and replaced the older of the two, but that did not solve the problem with the system. Right now the PLC has the above light on and the two drives have a BF light flashing, The power rail units have the SF on and the remote I/O has a BF flashing. I checked the cable and rails that go from one power rail unit to the other and it is all good not shorts or grounded wires. I have a spare cable for the Profibus and so I went through and replaced all the cables, one by one, on the network to see if one of those was bad, still no luck. I took the connectors from one of the drives and checked it over, it seemed good so I swapped all the connectors on each device to see if one of them has gone bad and again not luck. When I go online with the PLC on the MPI port I can see the PLC but none of the Profibus nodes can be reached, they all have a red error box on them including the PLC. After looking at the Siemens web site it told me to re-download the hardware config file to the PLC and that should get rid of the SF light. I did as the web site instructed me to do but still no luck. I am at a loss and am at the point of replacing the CPU of the PLC to see if that fixes the problem, OR HIT IT WITH A HAMMER AND SEE IF THAT HELPS. Any help would be great Thanks, Steve

[Groo 7]

Taken from the Siemens manual SF On can be one of the following: Hardware faults Programming errors Parameter assignment errors Calculation errors Timing errors Faulty memory card Battery fault or no backup at power on I/O fault/error (external I/O only) Communication error BusF Flashing (the CPU is the master) 1. Station failure. Check the bus cable connection to the CPU31x-312, or check whether the bus is interrupted. 2. At least one of the configured slaves cannot be addressed Wait until the CPU 31x-2 has powered up. If the LED does not stop flashing, check the DP slaves or evaluate the diagnostic data for the DP slaves. So it would seem one or more of the slaves cannot be reached, the first thing to do would be to look at the diagnostic data of the CPU, this should identify the missing slave/s. You can also add the relevant fault OB to stop the CPU failing and see what info you get in the OB TEMP diagnostic data. If all the nodes are down and if the network is wired correctly you could enable a node at a time using the resistor switch, moving away from the CPU to see if the network is OK with restricted nodes. Do you have profibus plugs with diagnostic led's on, these are useful. Fault finding any network fault can be painful. I had a resistor fault on a drive once that reflected the fault to a position about 6 drives down.

[JesperMP 2]

The combination of BF lights tells us that either the DP master (the CPU) is bad, or that there is a cabling problem, or one DP slave is so defective that it pulls the entire network down. Start by removing all DP slaves from the network, and reconnect one by one. Always remember to have the termination on for the first and last units in the DP daisy chain. If you encounter a DP slave that dont want to go online, investigate the cabling from the last good DP slave and the faulty slave.