Dell Multifunction Laser Printer 5535dn, Service Manual

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Diagnostic aids
3-53
Polygon printhead assembly
The printhead scans the photo conductor drum surface with a laser beam. It consists of four components: laser
diode (LD) card assembly, printhead motor, polygon mirror, and the start of scan card assembly.
1. LD card assembly — generates the laser beam. The beam is turned on or off according to a print data
signal coming from the system card.
2. Printhead motor/polygon mirror — the polygon mirror is mounted to the shaft of the printhead motor, and is
rotated at a high speed by the printhead motor. The mirror rotation shifts the incidence and reflection
angles of a laser beam to scan the photoconductor (drum) in a single direction. The laser beam reaches
the polygon mirror as it passes through multiple lenses, mirrors, and windows. The laser beam then arrives
at the photo conductor (drum) surface.
3. SOS card assembly — when a laser beam hits the SOS sensor on the SOS card assembly, the beam is
converted to an electrical signal (SOS signal), and detects the initial position where a scan starts on each
line.
When a laser beam is scanned across the photoconductor (drum) surface from one end to the other while
turning on and off the beam, one line of latent image is created. If the scanning by the laser beam is repeated
while rotating the drum, a two-dimensional image is created. The resolution in the scanning direction (from
right to left) is determined by the rotational speed of the printhead motor, depending on how quickly the laser is
adjusted. The resolution in the process direction (from top to bottom) is determined by the rotational speed of
the printhead motor. (The higher the scanning speed becomes, the sooner the scanning of the next row can be
started.)
Polygon printhead