Transfer Roll Assembly; Printhead Assembly - Lexmark W840 Service Manual

4024-XXX

Transfer roll assembly

The transfer roll assembly is driven by direct contact with the drum of the PC cartridge.
The transfer roll assembly applies positive charges to the rear surface of the media when the media passes
between the transfer roll assembly and the drum. The negatively charged toner image is attracted by positive
charges on the rear surface of the media. Thus, the toner image is transferred from the drum surface to the
media surface.

Printhead assembly

The printhead scans the drum surface with a laser beam. It consists of four components: laser diode (LD) card
assembly, printhead motor, polygon mirror, and start of scan card assembly.
1.
LD card assembly – generates a laser beam with the two LDs of LD1 and LD2. The beam is turned on or
off according to a print data signal.
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 laser beam in the drum axial direction. The laser beam reaches the
polygon mirror as it passes through the lens (L1), lens (L2), and window. The laser beam then arrives at
the 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 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
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Printer Service Manual
PC cartridge