1-56 Service Manual
4025-XXX
Xerographic Process During a Print Cycle
1. Charge
The Bias Charge Roll (BCR) places a uniform negative electrostatic charge on the
surface of the drum. The drum surface is made of a photoconductive material that
holds an electrical charge as long as the drum remains in darkness. Light striking
the drum discharges the surface charge.
The BCR is a conductive roll that is positioned slightly above the surface of the drum.
The HVPS supplies the BCR with two voltages; a negative DC charge voltage and
an AC discharge voltage that is used for electrically cleaning the drum (discussed in
Step 6. Clean).
2. Expose
The Printhead generates a beam of laser light. Image data received from the print
controller modulates this beam, turning it on and off according to image information
that is received from the host computer and software.
Through the use of a series of rotating and stationary mirrors within the Printhead,
the beam scans the negative charged drum surface. Whenever the print controller
sends a command to print a black pixel, the laser switches on long enough to shine
onto the drum at a single pixel point. That point is now discharged and slightly less
negative than the surrounding negative charge. The less negative areas are
considered positive. This discharge/no discharge process creates an invisible,
electrostatic image on the surface of the drum. This image is called a latent image.
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