Phaser 3250 Laser Printer Service Manual 2-11
Theory of Operation
Laser Unit
The Laser Unit is the core part of the Phaser 3250 and is controlled by a video
controller. The Laser Unit converts video data received from the computer into
an electrostatic latent image on the surface of the OPC Drum. This is
achieved by controlling the laser beam and exposing the surface of the OPC
Drum to the laser light. A rotating polygon mirror reflects the laser light onto
the OPC. Each face of the mirror produces one scan line. The OPC Drum
rotates at the same as the paper feeding speed. As the OPC Drum turns, the
laser scans, which creates the full page image.
The Horizontal Sync (HSYNC) signal is created when the laser beam from the
Laser Unit reaches the end of the polygon mirror and this signal is sent to the
controller. The controller detects the HSYNC signal to adjust the vertical line
of the image on paper. In other words, after the HYSNC signal is detected, the
image data is sent to the Laser Unit to adjust the left margin on the paper.
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