Sm102 problem

I have problem with sm102 heidelberg machine type 102f +l, machine Nr 535654, year 1993
Give the problem in the photo

 

HELLO sir the sheet detectors are dirty or there's a piece of paper covering it

 

Thanks for your reply
I need to know where is the sheet detectors and the number for each one

 

Looking at the state of your machine from the photo i would say give the 2 detectors a clean & that may solve your problem. (they are by the front lays)