UCBB Board- Isolated input issue

[mark68]

I've had this board and a ET300 on the shelf for a while and now just got around to using them on a controller conversion.
I have connected 3 quantity NPN proximity sensors to 3 seperate inputs at the lower end of CN2 inputs using numbers 7,8 and 9. input 8 fails to read the sensor which had me double check the wiring and sensors which both proved to be fine, each sensor goes from 24v to ground when activated and tested.

This is backed up by the fact if I move up to inputs on CN1 numbers 12,13 and 15 all three sensors regsiter fine.
I did double check my ports and pin numbers mutiple times.

This looks to me if input 8 is faulty on the board, I couldn't get the board led to light up and I swapped two sensors around to check this. Is there another way of testing these two pins. Have you seen this issue before?