AB 1769-L33ER changing to remote program

Good morning all.

I looked through previous posts and didn't find any help on my exact problem. I have a 1769-L33ER PLC running a water jet cutting robot cell that interfaces the operator controls with the robot controls. Last night they had problems with the cell not responding and investigated it for quite a while. I finally got called in at around 3:30 am. The PLC was set to "remote" on the switch on the front of the PLC. When I went online I found the PLC had switched to remote program mode. Since there is no one else with PLC access in the facility, I know that no one went online and switched it from remote run to remote program. The box is not checked on any of the ethernet modules to cause a major fault on the PLC if communication is lost in run mode and there is no fault routine in the PLC that would cause this. Does anyone know what would cause this? Has anyone ever seen this before? Would someone accidentally causing a short on the 24 VDC power during their troubleshooting efforts cause the PLC to switch to remote program to "self protect" the outputs if that happened?

Note: I have experienced this with other AB PLCs and never found out why it happened but I always had a suspicion it was something to due with a short on the 24 VDC circuit.

Just a WAG but.... if someone opened the door and flipped the switch to program then back to remote the PLC will stay in remote program until you change it in the software or flip the switch to RUN then back to remote, odds are they flipped the switch and did not tell you.

geniusintraining said:

Just a WAG but.... if someone opened the door and flipped the switch to program then back to remote the PLC will stay in remote program until you change it in the software or flip the switch to RUN then back to remote, odds are they flipped the switch and did not tell you.

Click to expand...

This would be my first thought as well.

When less-qualified troubleshooters have been working on something for a few hours, "we didn't touch that, honest" is unlikely to be true.

A-B PLCs *can* reboot into Remote Program mode if they are configured to do that when recovering from a fault that cleared the user program. It's selected when you write to the EEPROM/Nonvolatile Memory. Short circuits on the power supply seldom do that, but lighting strikes and other surges can.

You mentioned that it's a waterjet workcell. I know that a major waterjet supplier that uses CompactLogix has runtime lease features that will shut down the machine if they are tampered with or exceeded, but I don't think it simply switches the controller to Remote Program.

The most likely explanation is the simplest one: somebody toggled the keyswitch without knowing what it does.

Someone's not telling you the whole story.