Abstract: When cover (8) of the laser printer (3) is closed, absence of the replaceable cartridge (15) or the shroud assembly (9) will activate both an electrical and a mechanical interlock. A moveable switch actuator (16) on the shroud assembly will be absent if the assembly is omitted and will not find a guide ramp (46) if the cartridge is absent, thereby assuring power to the light source remains off. A shutter (13) also blocks the normal light path and is moved aside by a pin (14) on the cartridge, and therefore blocks light unless a cartridge is installed. Walls (31) on the cartridge surround the shutter during normal use to form a protective light baffle. The laser printhead (2) is fixed within the shroud so that separation requires a necessary electrical cable (72, 74) to be disconnected.