Has anyone on the list ever experienced AB SLC digital input or output card trouble where one channel would fail while the remainder of the
card remains in service. For example, I had a 1746-IA16 where a 120 V ac signal was present at the card TBs but did not register in the card
while the remaining 15 inputs were functional.

Thanks,
Mark

 

Most PLC digital IO cards have isolating interfaces between the real world, and the card itself. If a single point is damaged (excess voltage/spike) then quite often the rest of the card is OK.

 

Yes, I have had that problem. The problem in your case, could be an opto-isolator damaged, and you will need to replace it, sometimes it is caused by problems in the line where that input is connected (probably to a field sensor) you should see physically the card and look the circuit associated with that Input and then try to fix it. If it doesn't work you probably should replace the card or translate that input to a spare and move that input in the ladder logic problem (using the replace function in RSLogix500 Software).

 

I've seen this before where nothing was wrong with the card- removed it and placed it back into the slot and it fixed it. (dust-I guess)

 

Ive never seen an input fail on an AB card but it is possible. I have seen several input failures on 984 800 series cards. That is just my experience. I have however had single point failures on AB output cards. Since the SLC500 input cards are only a couple hundred bucks, just replace it rather than mess with it yourself, its probably not worth your time. Or you can use ABs repair/exchange program and get a discounted refurbished card Fed-Exed to you and then you send your card back to them via regular ground shipment.

 

I have seen this. I can't tell you for sure its happened on a SLC. Why couldn't a single point fail while the rest continued to function?

Bob Peterson

 

dear sir,
In your case,Opto coupler may be the faulty.
bye

 

Yes this is common.
It is a good practise to leave some i/os free just in case the ones being used fail.
Gabriel

 

Had this and other problems with all PLC manufacturers' hardware - move to spare!

[ Even Linux soft PLCs can lose a channel of I/O apparently ]

RA