Lexmark C 540n, Service Manual

Page: 129 / 262

Diagnostic aids
3-39
5025-2xx, 4xx
Step 2: Expose
During the expose step, the laser fires a focused beam of light at the surface of each photoconductor (B) and
writes an invisible image called a latent image or electrostatic image for each color.
The laser beam actually discharges the surface only where the beam hits the photoconductor. This creates a
difference in charge potential between the exposed area and the rest of the photoconductor surface.
Service tips:
•
The laser beam passes through a glass lens as it exits the laser unit. If this lens gets contaminated with
toner or other debris, it will cause white or light vertical streaks on the page. Cleaning the lens solves the
problem.
•
Never touch the surface of the photoconductor with your bare hand. The oil from your skin may cause a
charge differential on the surface and toner will not stick properly. The result would be repeating patches of
voids or light print on a page. Then the photoconductor will have to be replaced.
•
The surface of the photoconductor is coated with an organic substance that makes it sensitive to light. Be
sure and cover the photoconductor when you are working on the printer so you don’t “burn” it. If exposed to
light for too long, it will cause light/dark print quality problems and have to be replaced.