Lexmark C912 Service Manual - Page 183

5055-xxx Theory of operation Processes and configuration In this printer, the toner of four colors (magenta, cyan, yellow and black) melts and deposits dots on paper, which record color image information. This printing process is called the electrophotography process. Electrophotography process In the electrophotography process, electrically charged toner exposes, develops, transfers, and is cleaned with an aluminum photosensitive drum. A photoconductive layer forms on the surface of the drum when the drum is exposed to light. The surface of the photosensitive drum is negatively charged, forming the electrostatic image on the surface of the photosensitive drum. This charge is directed to the photosensitive medium at a low voltage, reducing the generation of ozone to a very low level. When the drum surface is charged, the image is recorded by irradiating light from the LED printhead, forming the electrostatic image. The LED printhead array along with the Selfoc lens array provide a single-dot line of the image, in a one-to-one arrangement. The image data from the printhead controller causes the LED to emit light in black dots. These black dots form an image of dots on the photosensitive drum. The LED printhead minimizes the displacement of images during the color print process, when images of multiple printheads overlap, causing dot position accuracy to be much higher. Since light from the volume of the LED array varies depending on the LED printheads, the light emitting value is recorded in the EPROM of the printer controller. When the LED printhead is replaced, the light emitting value should be entered for each printhead while the printer is in maintenance mode. Since the LED printhead and EPROM on the printhead controller board of this printer are paired, the EPROM on the printhead controller board should also be replaced whenever the printhead is replaced. Diagnostic aids 3-33