1771 A2b Bad Slot

CaspianSage

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Jan 2017
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Greetings Friends,

I have a 1771-A2B with one slot not recognizing inputs nor will it turn on any output. It started acting up intermittently on a couple inputs, now nothing.

It is Slot C4- D4 only using C of course. I have taken the chassis apart completely to examine the board and I can see no physical damage.

I also have read out all of the connection points from the socket to the back of the board and the solder traces. I also squeezed (Tightened) and cleaned the socket pins to make sure the card was getting a good connection. I am coming up empty.

I re-soldered the holes that are pass through near pin 12.

Although the card sees an input, the PLC does not in the input image table-

I put a "-1" in the output image table to set all output bits and nothing turns on for that slot. I tested this with several input and output cards and every other slot works.

I know they are somewhat inexpensive on Ebay but I would like to find out where the failure point is.

Any Ideas?

Thank you for your time.... Sincerely!
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Last edited:
It's been a few years since I touch these, but I recall that most of the issues were related to the failed chassis DIP switch that caused PLC or adapter to read slots incorrectly.
 
It's been a few years since I touch these, but I recall that most of the issues were related to the failed chassis DIP switch that caused PLC or adapter to read slots incorrectly.


I was wondering about that possibility, kind of shrugged that off as unlikely but now that you mention it that makes sense. I will check that out. Maybe dirty contacts in the switch......

Thanks!
 
Are you sure that this is not controller or adapter?


I am not sure what you are asking... If you mean am I mistaken as to what I have, well interesting question.

I am using a PLC 5/20, I don't think an adapter has an I/O image table.

I first started seeing the problem with an actively running program not registering inputs.
 
How do you know that 5/20 is OK?
Did you try it in a different chassis?

Yes, First thing did, I have 3 PLC5s and tested with all of them. I changed the chassis out in the working system so I could use slot 4. Test Benching with 2 of the other plc5s in the defective chassis- Its just the one slot that is a problem. No problem with any of the 3 processors in the other chassis.

I want to use this chassis for remote i/o. I can probably get by with out that slot but I don't want to use it in case other slots fail.

Thank you!
 
Solved -Loose Pins in Processor Socket

Went back through all the socket connections for the PLC Slot, first slot in the chassis.

Some still looked looser than they ought to be.

I used a small screw driver and pushed them back together, first left to right then right to left, making the gap between them as small as I could with just enough room to slide the processor into the slot.

All works now but unfortunately I got one set the pins in one slot to tight and when I put the processor back in, it pushed them down into the connector, still makes contact but now I need to fix that or get another socket..

Anyway Problem solved. Loose pins in processor socket.

Thank you!
 
Thank You!

Just keep in mind that chassis DIP switch setting for RIO adapter in not the same as for the processor.

Exactly, I have the settings for RIO - The chassis is repaired now and working fine.

Thank you for your input here,

Although when you mentioned the processor possibly having an issue I knew it was ok, but your post prompted me to check the pins for the processor again and that is where the problem was.

I really appreciate you staying with this topic through resolution of the problem. So a big thanks!

This is one of the best forums on the net I use.
 

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