Abstract: A mechanical schematic diagram showing the paper flow path through a xerographic copying machine and an associated sorter is illuminated when a paper jam occurs or when the supply of paper, toner or fuser oil is depleted. At the same time the copier is shut down and a flashing light on the diagram at the approximate location of the problem source is illuminated. Steadily illuminated lights indicate the positions of paper sheets which must be removed from the machine before normal operation can resume. Depleted consumable items are also identified by flashing lights indicating the location of the cause of the interruption. Thus the machine operator is immediately able to determine the cause of the interruption and the corrective action required.