HP 2300d Service Manual - Page 89

Laser/scanner system At the laser/scanner assembly, laser beams focus onto the photosensitive drum and discharge the drum's negative potential. This creates a latent electrostatic image, which later is developed into a visible image. The laser diode beams shine onto a scanning mirror. As the mirror rotates, the beams reflect off the mirror and sweep the page from left to right. A set of lenses and mirrors focuses the horizontal sweeping beams through the beam access slots in the rear of the toner cartridge and onto the photosensitive drum. Because the beams sweep the entire length of the drum while the drum rotates, the entire circumference of the drum can be covered. At the beginning of each sweep (before the beams reach the drum), the beam detect mirror reflects the beams. The momentary pulse of light goes to the engine controller PCA, which converts the light to an electrical signal that is used to synchronize other activities in the printer and to diagnose problems with the laser/scanner assembly. Portions of the drum that are not exposed to the laser still contain the uniform negative potential that was placed there by the primary charging roller, but the portions that have been exposed to light have been discharged to ground to form the latent electrostatic image. Figure 17. Laser/scanner system ENWW Chapter 5 Theory of operation 87