90-30 CMM311 OK LED blinking

Hi,

We have a 90-30 CPU (374 Plus) with a CMM311 on Rack 0. It is using RS232 to communicate with a Siemens MP270B touchpanel. It was working before, but the PLC experienced a fault the other day. Ever since, the OK LED on the CMM311 is flashing, not constant. The restart pushbutton does not fix it. I've uploaded the hardware configuration again, but it still does not fix it. Any suggestions?

A flashing "OK" light means that there is a module error or fault, it may show you details in the CPU's fault table, check both the CPU and I/O Fault tables. You can DL a manual by searching for the module part number, IC693CMM311 at www.gefanuc.com/support to look up what a 'rythmic' flashing of the OK light means.
HTH

I guess I didn't mention this, but the fault tables were cleared, and they are empty when that light is flashing. The only thing I could find regarding a flashing OK for the CMM311 is that there's an error in the diagnostic, yet nothing shows in the fault tables, and the hardware configuration is correct

If what you say is accurate and you have not left out anything else, you have a bad module. You can replace it or have it repaired. To purchase a repaired unit from GE Fanuc see if they have an IC693CMM311RR available, this is the quickest way to get a repair.

We had a spare module, so we replaced it. Still the same error. I brought the old unit back to my test rack on my desk, and it works there. When I stop the PLC, a system configuration mismatch appears on that slot (0.10). I can move the card around and change the configuration file, yet the same fault still appears, and only when I stop the PLC. I was leaning towards a faulty backplane, but the 3 existing modules work perfectly. Also, since when I move the module to other slots, it was still exhibiting the same behaviour. Kinda stumped right now.

What was the nature of the fault that started this behavior?

A lightbulb on a 129VDC bus shorted and tripped a breaker. The negative of this bus was tied to an MDL632 125VDC Pos/Neg input, and a discrete input off some relay contacts. We believe the overcurrent may have caused the fault (as it faulted at the same time). We've been having problems with that module (replaced it, it isn't being recognized by the PLC), as well as the CMM311. Thing is, the modules are 7 slots apart, and none of the modules in between were affected, thus making me skeptical of a backplane problem. Both existing modules are functioning on my test bench.

I wouldn't rule out a backplane problem. The CMM311 uses backplane lines that discrete I/O modules don't use. Furthermore, the combination of a damaged backplane and a damaged MDL632 may compromise the signal enough that a CPU on the damaged backplane can't recognize it, but when you move it to an undamaged backplane it looks OK.

If I were you, I would flag all of the modules that were in the system when the fault occurred in case they start showing problems in the future. The event may not have killed them outright but its a pretty good bet that it shortened their lives. You would be wise to make sure you have sufficient spares on hand