siemens s7-300 plc error

hi,
i am facing problem with s7-300 plc(cpu 312c). neither i am able to down load nor able to upload any project done by me in simatic manager. my plc is permanently SF (red) mode. in accessible node no node is visible.
pls tell me the possible problems and remedies.
thanks.

Hello frıend sf led is light when cpu fault or fault in module with diagnostics capability.I thing you change some block in the plc or your plc software is old version. good luck

Is this a new CPU or was it working and the SF fault came up recently?
If this is a new CPU, then is a MMC memory card plugged in?
Have u tried to do a memory reset using the keyswitch?
Do you have the right cable and configured correctly?

reply

hi dear,
I have gone through all possible diagonestic(resetting MRES key also) but still problem remain same.
thanks

I ran into a similar issue earlier this year on a project with a CPU315-2DP processor. When the memory became corrupted, the plc shut off ALL communication and was basically dead in the water. The only fix was to replace the MMC card with a new one (or find a piece of equipment capable of clearing the MMC memory) and reload the program.

I do not understand why Siemens does not provide a method for clearing out the memory to allow an opportunity to fix the problem. I do understand the fail safe mode of faulting when their is a problem with the PLC memory but at least allow a guy to clear the memory, re-establish communication and fix the problem.

Here is the real kicker, there was nothing wrong with the program! It appears that when I loaded the program using the ethernet interface, the program would get corrupted. When I loaded the program serially, everything worked fine. I spent a lot of time with tech support trying to figure out what was going on with no real answer. If I even tried to update a particular DB, FC or FB using ethernet, I would crash the PLC 50% of the time. I even upgraded to the latest SP and hot fixes per tech support with no difference.

I wound up going through several MMC cards until I quit modifying the program using ethernet(lots of egg on my face too). I could monitor the program just fine using ethernet but had to do all modifications serially. What a pain that was because the PLCs were quite a distance away.

Still to this day I have no idea what the problem was nor does tech support. I have to assume there may be some sort of conflict between various PLC programming software packages on my laptop computer but that is just a guess on my part.

I may have just had a similar problem. I could no longer download to a 315. The key switch 'reset' did not help. The following Siemens Entry says that you can only reset an MMC if the data is invalid for the CPU, otherwise the MMC is only initialized. http://support.automation.siemens.com/WW/view/en/21830698

So, I put the MMC in a 314 (which was invalid for the MMC data) and then used the key switch reset procedure (Hold switch in MRES for 9 seconds until STOP LED lights continuously, then let go of the switch, then hold the switch in the MRES until the STOP LED stops blinking quickly.) I then put the MMC back in the 315 and it worked fine. This seems to have completely erased the MMC. I had also powered the 315 without an MMC in the meantime. Maybe this might help you.

I had to times a similar fault.

I could work a whole time with the cpu. But after a couple of days i got the message "Bus faulty". And i found no solution for this.

So I sended the cpu back to Siemens to repair.