CompactLogix didnt start - Firmware revision?

I have 3 1769-L32 with Firmware v20.12 - Had an electrician turn off the wrong breaker and shut them off. When I power them back up they didn't go into run mode, I can't recall which LED's were flashing but I think OK was one of them.

These PLC's had a CF card with older firmware version (v17) of the program and they are NOT set to load the program from the card on powerup.

Also during this time they were unreachable through Logix5000 software but their webpage was accessible. All modules were lit indicating they were OK just the proc was flashing.


I finally started them by placing the key in prog for 20+ seconds, then run, which eventually worked. But I had to do that sequence several times before it worked and lit the PLC up. After I got them started again the controllers ALL had Code 03 and 23 in it.

I have had those PLC's power down in the past under v17 FW and didn't have a restart problem like this, this is the first time they have been shut off like this since the update and the only thing new about them is the v20 Firmware.

Is there a problem/Feature in the v20.12 FW that would account for this?

I did learn just recently that switching the keyswitch from program to run mode three times will clear a major fault and return a PLC to run mode. Is it possible that the PLC's had a major fault? I thought the OK light was red when there was a major fault, though, so perhaps not

Well, that sounds exactly right. I had no idea. Thanks for that, I'll have to fault them on purpose now to check that out.

Nice tip