Hello all,

We recently experienced an odd occurrence where a 410-5H system with latest FW and PCS7 V9.1 SP2 UC05 caused a self memory reset on the CPU without user prompt. I am curious to see if anyone has experienced something similar or has any clues as to what maybe going on.

The PLCs were initially placed into STOP via the ES due to another issue and left in that state. About one week afterwards, the facility experienced a power outage that lasted 3 hours. This caused the PLCs, switches, PCs, and generally all associated PCS7 hardware to hard fault. After the 3hours, the power came back, all PCs and PLCs and balance of equipment energized concurrently. The PLCs at this point had both SYNC LEDs lit, and generating a sync error. Upon review of the CPU logs, post power outage, we found that the PLCs initiated a memory reset on themselves and fully cleared. This was without any user request or interaction.

The PLCs naturally have flash based memory with new fully charged batteries. We would not have expected something like this, and personally I have never seen this in the countless times I have previously power cycled 410 controllers. Any and all ideas are welcome.

Update: After further digging I found a thread that seems almost identical to the issue we had: S7 400 memory reset automatically - 166658 - Industry Support Siemens Does anyone know why a PLC will memory reset on sync module failure, and if there is anyway to avoid this as its extremely damaging to a running plant. BTW, in our case our modules were not failed UPDATE: (but I did replace the fiber optic cable from a 3rd party one to the official Siemens 410 sync cable, which resolved the SYNC error).

Thank you!

Hi Oreca, your input is most appreciated. Where can I find these details (FAQs, manuals, etc...) as to what can cause memory resets of PLC STOPs on its own. We actually have experienced both in the last 3x months. I have dug and dug, and worked with Siemens support, but can't find any specific details.

I will see if I can find the diag buffer from and upload it for review. Thanks again!

Hi Oreca,

Please see diag buffer attached from CPU 0.

Also please note that we are at firmware v8.2.4, and to my knowledge this is the latest rev. That being said, I recently spoke with support and was advised that new CPU firmware is expected in the next 2-3 months. It won't address this specific issue, but just giving a heads-up that an update is coming.

Furthermore, I think based on your direction and piecing everything together, I have the following sequence of events mapped out:

1. The PLC started after a power loss with a SYNC error, and this is to my knowledge when a memory reset occurred within 60 seconds of them powering up.

2. I failed to mention, or make the connection till now, that the PLCs fiber sync cable was not the official Siemens cable supplied with the 410, but a 3rd party cable that a system integrator had lying around from other projects. I had the cable replaced with the Siemens cable and this immediately resolved the SYNC error (maybe coincidence, or maybe root cause).

3. At this point the PLCs were already reset, and until I recently reviewed the 410 system manual, I didn't realize that a SYNC error on startup will automatically force an internal memory reset on these PLCs.

Based on the above, I feel this is likely what happened, but any additional input is certainly appreciated. Thanks again!

Oreca,

Thank you for your time in reviewing the buffer, and your suggestions. I agree with your assessment that something happened here during link-up that caused this reset, and likely it was the cable. We haven't had this issue since the cable was replaced about 2.5 months back.