Old extruder line. CPU 315-2 DP, five ET 200M slaves on PROFIBUS, 1.5 Mbit. Slave 5 is in an outdoor panel by the silo.
Every time that panel loses 24V, which is a few times a week now it's cold, the whole CPU goes to STOP. SF on, DP LED red. Buffer top entries, near enough as written:
"STOP caused by rack failure OB not loaded (OB 86)"
"Distributed I/O: station failure, station 5"
We put a new DP cable on slave 5, checked the terminators and swapped the IM 153 with the one on slave 4, and it's the same every time the panel drops. Losing a whole line for one outdoor slave, and I'm out of ideas. Is it the CPU firmware? It's an old one. Or is there something in the CPU that decides a missing slave should stop the lot, I think there must be.
It's not the cable and not the firmware. The buffer already told you: OB86 isn't in the CPU. Which STEP 7 version, and have you got the project? Look in the Blocks folder for OB86.
STEP 7 5.5. I've got the project. Blocks folder has OB1, OB35, a pile of FCs and DBs. No OB86. No OB82 either, and I think that's the whole story.
Add OB86, OB82, OB122 and OB85 to the project, empty is enough, and download them. The CPU then logs the station failure and keeps running. Inputs from slave 5 read zero while it's gone, so make sure the logic can live with that.
The 24V dropping in the outdoor panel is a separate problem and still needs fixing. Have a look at what the power supply there is rated for at the temperatures you're seeing.
Loaded the four empty OBs last night. Panel dropped again at 06:10 this morning, buffer shows the station failure and the return, CPU stayed in RUN. Line kept going, the silo feed just stopped until the panel came back.
So the buffer had already told me on day one, there was no OB86 in the CPU and a 300 stops on a rack failure it can't hand anywhere. Four empty OBs and it carries on.
Still have to find out why that panel loses 24V. Power supply is a 2A unit feeding a heater and the IM, and my money is on the heater pulling it down. Thanks dieter_k and sergio74.
A 2A supply with a panel heater on it. Look there first.