I have a TAC50-04 that is giving me a 1021 & 1687 faults. I changed the communication line to a spare shield. The elevator would run and then randomly stop and throw those faults along with a 1684 fault. Not the elevator won’t run. When trying to run on controller inspection it will fault out. On Automatic I have my INCTM & INHAM inputs active. However when I try to run it everything clicks and it tries to run but then faults out and all the Cartop inspection I/Os come on and off. Any help is appreciated.

If you’re seeing just the car top inspect I/O drop out but not INHAM then I’d try just replacing the S24 card that runs those inputs. I’d also be curious if your P24 is on that board is dipping or dropping out when this happens. Maybe a short pulling down P24.

I've had to change the ethernet cables also.

So this wound up being excess noise on the comm channel due to a faulty CNA card in the door controller. It would intermittently disrupt the communications with the CNA cards so it wouldn't recognize the I/O's on the cartop board. Replaced it and problem went away!

Wow. What kind of door controller? BiParting?