ML1100 D.I. causes memory loss

We have a machine that keeps losing its program at random intervals; sometimes 2x-3x in a shift, sometimes will go over 1wk without issue. I had a hard time getting a new battery for it, took over a month. After receiving and replacing the battery it continued to lose its program, so I have a new PLC on order.

As I'm waiting for the new PLC to arrive (Micrologix 1763-L16AWA) I received a report from operators that the PLC loses its program every time they push a certain button. It's a button for a manual function that only gets used in one certain situation, not very often. I hear this and it sounds like nonsense. I've never heard or seen anything like it and my first instinct was to write it off, but i went to investigate nonetheless and found it to be absolutely true. It's a simple circuit: 120v>wire>button>wire>Digital Input. I tested for shorts, grounds, etc, nothing. All good. That digital input is bad, I tested by disconnecting the button and running a jumper from 120V to the input, and as soon as it sees that input it pukes the program.

Just curious if anyone else has seen this before. Total curveball for me.

Try moving the input to another unused one... guessing its not noise but a failure on the 1100's input board, I have had similar issues on a SLC card before

Also next time we stock the batteries and ship the same day https://www.plccable.com/allen-bradley-plc-battery-1763-ba-micrologix-free-shipping/

Not quite the same problem but we had a machine that every time a certain button was pressed the plc would re-boot. I also traced this to a certain input I also tried to remove the wire and link it to the supply & the same thing happened. It turned out to be a shorted solenoid coil that took the supply low when the button was pressed i.e. it was not the input but an output that was turning on when the button was pressed thus causing the plc to fault then restart.
I suggest that this could also be a cause although in your case it is spiking the PLC causing corrupt memory, I do know someone who had this problem on an old SLC that were prone to spikes causing program loss.

strantor said:

...the PLC loses its program every time they push a certain button....

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Ah, simple solution: just change the label on that button to "lose your mind."

I've shorted the pins to each other on a OW16 expansion card (don't ask) and had the PLC lose it's memory. I would also move the input and see if the problem follows.

I have had AC powered ML1100's lose their marbles if there is a "brownout" feeding the power supply. Make sure that notorious button is not suffering from some other electrical issues that is causing a droop on the voltage feeding the brain. I have a preference for DC powered Micrologix partly because of this.

Sounds as bad as SLC500's they were prone to that, although I have never lost a program on an 1100 or 1400 personally.

parky said:

although I have never lost a program on an 1100 or 1400 personally.

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I have a brand new one here that anytime its powered down it will lose the program and faults out... but out of the hundreds I have used that is the first one so I am not complaining at all, they are electronic and are going to fail someday it's just a matter of when.

When you say "loses its memory" it would be in fault mode then, Do you read the fault before reloading the program. I have seen this before a lot on the ML 1000's with a retentive data loss fault or something similar. I was told suppression on outputs, poor grounding or poor supply power.

roxusa said:

When you say "loses its memory" it would be in fault mode then, Do you read the fault before reloading the program. I have seen this before a lot on the ML 1000's with a retentive data loss fault or something similar. I was told suppression on outputs, poor grounding or poor supply power.

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It runs fine, never faults and does everything it should, until.... you power down, once you power up again everything is gone and the fault light is flashing, I did look at the fault but forgot what it said, I think something about memory, I even tried loading a MM1 but that did not help and would not let the program reload until you cleared the fault, I put it up for sale on Fleabay, figured someone could use it as a trainer or a test PLC

https://www.ebay.com/itm/373223496405