I'm new on the floor here so bear with me. ControlLogix 1756 L71 with a 1756 EN2T in slot 3 and four 1734 AENTR racks hanging off a Stratix 5700. One rack, the one on the case sealer, throws 16#0204 a few times a day. The other three never do.
The old hand who retired told me to check the counters on the EN2T webpage and then left. I found the page, Diagnostics, Ethernet Port, and FCS Errors says 19,342. I've no idea whether that's a lot, or what it's pointing at.
I swapped the sealer rack's cable, power cycled it and put the RPI to 50ms, and it still does it. I guess the EN2T is on its way out. Is 19,342 a lot, and does that number tell me anything about which end of the sealer rack's cable to go at?
rpi on that rack vs the others? and pull up the same counters on the switch port that goes to the sealer rack, if the errors are there too its the rack side. dont swap the en2t yet. 19k over how long?
All four racks are at 20ms, I only put the sealer one to 50ms and it still does it. Switch port to the sealer rack, zero errors, IT had a look. The port to the EN2T itself, gi1/1, has CRC errors, roughly the same number. No idea how long either, the page doesn't say when it started counting, and I'm not sure it ever gets cleared.
Post a photo of the EN2T's own patch cable, the plugs, both ends. Was it made on site? The counters on that page are for the EN2T's port only, the link from the module to the switch. FCS errors there are frames arriving at the module damaged, and the switch's CRC on gi1/1 is the same story told from the other end. One link, one cable, two plugs. Nothing whatsoever to do with the sealer rack's cable. There's a Reset Counters button on the Port Diagnostics tab in the module properties, if I remember right. Reset it, wait an hour, read it again. If it's climbing, it's live.
Reset from the Port Diagnostics tab, it was there. One hour, FCS 210. So it's live. Photo attached of the plug on the EN2T end. It's hand crimped, clear plug, and one of the wires doesn't look like it goes all the way to the end. The drawings show a factory lead, which isn't what's in there.
That plug is your problem. A short strand in a hand crimp is a bad contact that works until it doesn't. The sealer rack is the only one showing it because a damaged frame hits whichever connection is unlucky that second, and that rack probably has the least slack in its timeout. Or I'm wrong and it's just the busiest. Cut the plug off, put a factory made shielded lead in, reset the counters, zero after an hour. Leave the spare EN2T on the shelf. There's a writeup on reading these counters here: https://plctr.com/advanced-troubleshooting-techniques-for-plc-systems/
Factory lead in, EN2T to the switch. Reset the counters Tuesday morning. FCS 0 after an hour, 0 at end of shift, still 0 today. The switch port gi1/1 CRC stopped as well. No 16#0204 on the sealer rack in three days.
Bad hand crimp on the EN2T's own patch cable, the whole time. The FCS counter on the module page was counting that link, not the sealer rack, and a factory made lead cured it. The EN2T was fine all along, so the spare stays on the shelf.
What I still don't get is why it was always the sealer rack and never the other three. Pat's guess is as good as mine. Thanks pat_k, ramonv.
hand crimps. every plant has one and its always in the worst spot.