HP LaserJet 4250 Service Manual - Page 120

Pickup-and-feed system overview The pickup-and-feed system consists of a motor, various rollers, and sensors that detect the presence of media, transport the media into and through the printer, and deliver the media to an output bin. During the transport process, if the media does not reach specific sensors in a specified time, the microprocessor on the dc controller PCA halts the motor and a jam message appears on the controlpanel display. Laser/scanner system overview The laser/scanner system forms a latent (or potential) image on a photosensitive drum according to signals that the microprocessor on the dc controller PCA sends. The main components of the laser/scanner assembly are the laser-driver PCA, the scanner motor, and a six-sided mirror. The dc controller PCA sends image data signals to the laser/scanner assembly. The laser/scanner PCA converts these data signals into a laser beam that strikes a sixsided mirror. The mirror reflects the light onto a photosensitive drum (in the print cartridge), creating a latent image on the drum. Image-formation system overview The image-formation system uses toner in the print cartridge to transfer the latent image on the the photosensitive drum to the media. Heat and pressure (from the fuser) are used to permanently bond the toner image to the media. The photosensitive drum (in the print cartridge) receives a uniform negative primary charge. The laser beam neutralizes areas of the drum surface to create the latent image. When the areas that are exposed to the laser beam come in contact with toner, the toner is attracted to them The transfer roller applies a positive charge to the back of the media. The positive charge attracts the toner image from the photosensitive drum and transfers the image from the drum to the media. The media then passes through the fuser, where heat and pressure are applied to permanently bond the toner to the media. 106 5 Theory of operation