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This Laser Printer creates an image on paper using a technique called laser electrophotography. The printer uses the electro-
graphic process known as Discharged Area Development, or “write black”. In this process, a digitally modulated laser scans later-
ally across a rotating OPC (Organic Photo Conductive) drum that has been negatively charged. Wherever the OPC drum is
exposed by laser beam, the image is written and toner is transferred.

To generate a color image, the OPC drum suitably rotate to the image length, one for each primary color and black. During each
successive pass, the laser exposes the portions of OPC drum that correspond to the primary color’s component of the image. Toner
is attracted to the laser-exposed portions of the OPC drum.
As each color layer is developed on the each OPC drum, they are transferred to the accumulator belt until all four color layers even-
tually reside one on top of the other on the accumulator belt. At this point, a sheet of paper is advanced under the accumulator belt
and the toner is transferred to the sheet of paper. The paper advances to the fuser, where heat and pressure permanently bond the
toner to the paper. From the fuser, the paper is driven to the output tray.

A cleaning blade scrapes residual toner from the OPC drum before the next primary color toner is applied to the OPC drum. This
prevents contamination of the next color layer. The cleaning blade is in constant contact with the OPC drum.
An accumulator belt cleaner scrapes residual toner from the accumulator belt. This prevents “ghosting “of the next print. The blade
only comes in contact with the belt after the accumulated toner layers are transferred to the sheet of paper

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The charging roller, comes in contact with the OPC drum surface and charged to approximately -1100 volts, and ensures a uniform
negative potential of approximately -500 ~ 550 volts on the OPC drum surface by the charging roller, depending on the selected dot
per inch printing and ambient temperature. 

As the OPC drum rotates, the uniformly charged OPC drum is exposed by the modulated laser beam. The vertically-moving OPC
drum passes in front of horizontally scanning laser beam, and the negative charge on the OPC drum surface are neutralized by the
laser beam. This forms a latent image.
Laser output power is either approximately 0.3 mW or 0.5 mW on the OPC drum surface, depending on whether the printer is print-
ing in 1200 dots per inch (dpi) mode or 600 dpi mode. The laser exposure, the negative potential on the OPC drum varies from
approximately -500 ~ 550 volts (unexposed) to -50 volts (fully exposed).

1.Charging (See P.122)

5. Paper Pickup (See P.124)

2. Laser Exposure and Scanning (See P.122)

6. Toner Transfer to Paper (See P.125)

3. Developing (See P.123)

7. Fusing (See P.126)

4. Toner Transfer to the Accumulator Belt  (See P.124) 8. Paper Exit and Paper Switchback (See P.127)

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A laser diode generates the laser beam, and lenses and mirror in the laser scanner direct the beam to the OPC drum. The beam is
made parallel by the collimator lens and is directed at the rotating polygonal mirror, attached with the polygon motor. The polygon
mirror rotates at a constant revolutions approximately 22,000 per minute. This transforms the beam into a horizontally scanning
beam, which is directed through the primary lens, altering the beam’s angular rotation motion into a constant horizontal motion. The
toric correction lens corrects the beam for any vertical misregistration. Next, the beam reflects off of a mirror and passes through a
window where it scans across the rotating OPC drum. At the beginning of each horizontal sweep, the horizontal sync mirror deflects
the laser beam to the horizontal sync sensor. This informs the main board that the laser beam is beginning its horizontal sweep and
that it can begin to modulate the signal with the data to be printed on that line of the image. 

As the OPC drum continues to rotate, it passes by the developer roller. The developer roller is charged to a potential approximately
-200 volts (350 VAC p-p). Toner is attracted to the exposed portions of the OPC drum in reverse proportion to the negative charge.
The greatest amount of toner is transferred to the most positive potential. The developer roller rotates at 1.33 times the speed of the
OPC drum to ensure a constant supply of toner.

Inside each developer is a toner supply roller that rotates in the opposite direction from the developer roller. This supplies a layer of
toner onto the developer roller. The doctor blade smooth and evenly distributes the toner on the developer roller. Gear-driven pad-
dle churn the toner and keep it fluidized and moving towards the developer roller.

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As the OPC drum rotates, in contact with the accumulator belt, which is rotating at the same speed. Located under the accumulator
belt at the contact point with the OPC drum, the first transfer roller carries a charge approximately +700 volts (FTR voltage). This
strong potential attracts and holds the toner from the OPC drum to the accumulator belt. The four color layers create while the accu-
mulator belt makes one complete rotation. 
Any toner remaining on the OPC drum after the transfer to the accumulator belt is scraped off by the OPC drum cleaning blade,
which is always in contact with the OPC drum. This leaves the OPC drum clean for the next layer of toner to be transferred from the
developing roller into the developer.

The cam-shaped pickup rollers are driven by the BK (monochrome drum cartridge) drive motor and force a sheet between the
paper feed rollers in the optional lower Input tray. The pickup roller completes only one rotation to pick a sheet of media from the
paper cassette. This will push the sheet of paper to the paper feed rollers but does not pick a second sheet.

The paper feed rollers in the optional lower Input tray advance the sheet of paper to the registration roller. The paper is driven lightly
against the stationary registration rollers to create a slight buckle in the paper, aligning the sheet of paper. At this point, the paper
remains stationary (since the registration roller clutch in the paper feed unit is not yet energized) until the image is ready to be