Siemens s7-300

Dear all,

I am a hydraulic engineer (fluid power) and I have basic knowledge in the PLC.

I met a root on a machine:

During a fault diagnosis on a PLC SIEMENS S7-300, it turns out that the reason given by the manufacturer of the machine is that the MMC memory card is damaged and must be replaced by a new and programmed again.

The Stop LED blinks slowly indicates that according to my research on the internet, a reset (reboot) in a well defined procedure siemens.

My questions are:

1) What is the risk of such action: A reset can erase forever the machine operating program?
2) if I remove the card, the PC goes into state RUN, more red led as if it were functional again.
Why this?

3) If I replace the card with a new one, but the same characteristic but blank, this can work?

4) What you think are the causes of failure of the card?

I would add that for several days the PLC was shut down voltages for welding requirements, and the failure occurred when the power is restored to the controller: is that it can influence?

Thank you for your information, and if possible with simple words

bruno

Hello Bruno,

The reset procedure (set RUN/STOP switch to STOP, hold the switch down in the MRES position for 3 seconds until STOP LED stops blinking, then release, then MRES for a very short time, then release) will copy the contents of the MMC into the memory of the CPU, if the contents of the MMC are ok. If this doesn't work, try again, because it can be difficult to get the "very short time" correct. If that doesn't work, it could be true that the MMC is corrupt, and if a new one is needed, the program must be downloaded with STEP 7 software.

Thank you sigmadelta,

if I understood the procedure given by Siemens (https://support.industry.siemens.co...efault-reset-or-overall-reset)?dti=0&lc=en-WW), allows to recharge (re-download) the program from the MMC to the CPU? if that program is correct/no corrupted of course.

So there's no risk of erasing the recorded program in the MMC?

Any idee about what happened with this MMC ? welding can explain this root ?

Bruno

No, the memory reset procedure does not reload the program into the CPU (RAM).
One of two things can happen when a memory reset is started.

1. If there is a valid hardware configuration on the MMC, and it matches the CPU, then the memory reset reset the actual values of DBs on the MMC card to the initial values defined by the programmer.
or..
2. If there is a corrupt hardware configuration on the MMC, or it does not match the CPU, the the memory reset erases the content on the card.

About when a program is loaded into an S7-300 CPU:

S7-300 has no backup battery, but a relatively powerful capacitor keeps the RAM content for a relatively long time (several days to my experience)

Upon power-up, the CPU checks the content of the MMC card, and compares it with the content of RAM. If the timestamp (and maybe checksum ?) of the blocks on both MMC and RAM match each other, the CPU just run with the blocks that are already in RAM.
If there is a difference, then the CPU loads the blocks from the MMC to RAM and then runs the blocks from RAM.

The reset procedure described in the link you supplied (holding down for 9 seconds) will erase the MMC, ONLY IF the contents of the MMC are invalid. It means you cannot erase the MMC by mistake.

The same procedure (except you hold the switch down for 3 seconds instead of 9 seconds) will copy the contents of the MMC to the CPU if the contents of the CPU are invalid. A successful copy of the MMC to the CPU is followed by a rapid flashing of the STOP LED for a couple of seconds, then the STOP LED staying solid.

If the STOP LED keeps flashing slowly, then the procedure is not successful, in both cases. You will need STEP 7 programming software and the PLC program in this case... which you should get whether you succeed or not, if you do not have them!

Thank you dear sigma delta and jasperMp for your support.

Ok, so if the MMC Card is corrupted/damaged, if we reset that, we erase the program/delate all data inside...

It possible to download the program from the CPU to the MMC without any laptop and step 7 ?

Thanking you

bruno

No. STEP 7 must be used to download your program. You must have STEP 7 software, a download cable, and a backup copy of your program. Only the manufacturer of your machine could supply the program. If they do not, they would have to come in and download it for you.

just to tell you that my problem is resolved: a new MMC with the program inside was sent is the sytem is functional again.

Thank you for your support sigmadelta and JasperMP.