Yesterday I worked on a photo eye barrier on an Itotec guillotine. A Currie & Co model PE330. The green LED which indicates the barrier is uninterrupted was out and stopping the blade from coming down. For guillotines the light barrier is an essential component in the safety system. If your arm breaks the light barrier the blade is inhibited from coming down. If the light barrier is doing its job then it should be very difficult for anybody to lose their fingers. The light barrier manufacturers go to great lengths to ensure that if there is any fault in their equipment then the guillotine defaults to its inhibit state. This means that light barriers are a common source of faults that stop the guillotine from working.
The power supplies all measured OK (a common source of trouble). Then I noticed that by applying pressure to some of the ICs the light barrier would work! This pointed towards an intermittent connection issue on the PCB. I couldn’t identify any cracked tracks, so I replaced all of the old IC sockets. That sorted the light barrier out and the guillotine was back up and going again.