SLC 505 Outputs not firing

[Mark_J]

Hello all. I have a few SLCs in my plant and of late we've seen a weird issue: The system will be running normally and then randomly the outputs will stop firing. The program is still executing normally and the output bits come on in the program but the outputs don't work on all the output cards. The processor is a series C processor with 1746 OB16 output cards. Anyone seen then this before?

 

[Ken Moore]

I have seen this behavior when one of the outputs (not fused), was connected to a load that was intermittingly shorting to ground. This would "drag" down all the outputs on that card, but did not bother other output cards. Next time it happens, try forcing all outputs off, then energize them one at a time until you find the problem. Or, (safer), next time it happens determinate the output wiring one output at a time.

 

[Mark_J]

Thanks for the Information.!