TT-1 issue

[cncjeff1]

Greetings All,
I received a call yesterday from a client in the south of the country, and it will be two or three days before I can get to him. All of a sudden, his TT-1 doesn't trigger. Twenty years plus working with Centroid and this is the first TT-1 problem I am seeing. Control is #6815. It is an M4oo fitted with an Aaeon 6890B, CPU7, Koyo PLC, and Centroid PLC3/3. According to the client, Input #1 never triggers in the Alt-I diagnostic screen. The only thing that he has not yet checked, is for continuity between the plug connection on the end of the wire, and the actual input on the PLC3/3. Any other ideas are welcome.

[cncsnw]

It is likely that he has a broken conductor in his TT1 cable (which is a single-conductor cable).