Service manual

ENWW Chapter 5 Theory of operation 87
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