One for the old-timers

Sherman, fire up the wayback machine!

Is there anyone on the forum with experience with a redundant GE Series Six system? A site that has one (installed in 1986) has been experiencing intermittent problems the CPU dropping out of run. If the backup CPU is still running the transfer to it happens OK, but both CPUs are prone to dropping out. They can restart the PLC using the keyswitch.

The system has been out of service for several months although not powered down. The batteries are all good, at least as far as the battery LEDs are concerned.

I have some thoughts on which modules to start replacing first, but I'm wondering if there is anyone else out there who remembers these beasts. Rootboy, I'm talking about you!

Check watchdog timers for each CPU. I don't those systems, but that was first thought.
Good Luck

The manual: http://www.cimtecautomation.com/doc...Six/Manuals/GEK-96602Asixplususer'smanual.pdf.

And this: https://www.nuovaelva.it/docs/Ge Fa.../INFOLINK/MORE_PLCS/SERIES_SIX/GEK-25366C.PDF.

TWS, I have all the relevant manuals. Thank you.

AKAHammer, I would not be surprised to find that the CPUs are stopping due to a watchdog timeout. But the programs have not changed between now and when they were running correctly.

So the question becomes what's the cause of the additional time per program scan. If it's because the redundancy controller is taking additional time to exchange data between the primary and the backup, then which module in the RPU should I replace? I was hoping there might be someone among the forum members who remembers the ways these systems fail.

Just a thought, probably nothing.
are the plc's tied together in the same panel?
are they connected to an ethernet switch?
have you tried to reseat the connections between the two systems, the cpu to the backplane, the i/o cards?

in regards to the reseat question, i have had this issue with AB plc's in the past due to dirty connections.
james

Both PLCs are in the same panel along with with the redundancy switch.
No ethernet involved. This system was commissioned in 1986.
Reseating the modules was one of my first suggestions to the site. That has helped in many Series Six systems.

The last one of these that I worked on was on a cardboard line, random faults and lockups.
After changing out all the electrolytic caps to no avail, I pulled all the cards and took an eraser to the contacts. Problem solved.

Reseating all of the modules into the rack is a time-honored first-step troubleshooting technique with the Series Six.