Lexmark C792 Family, Service Manual

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Print engine theory
Electrophotographic Process (EP Process)
The method that all laser and LED printers use to print is called the electrophotographic process. These
machines use differences in charge to manipulate and move toner from the print cartridge to the printed page.
Even though the basic EP Process is the same for every laser and LED printer, the specifics for each printer are
different.
Electrophotographic process basics
This printer is a single-laser printer that use four print cartridges (cyan, yellow, magenta, and black) to create
text and images on paper.
The printer has four photoconductors (sometimes called a photodeveloper cartridge or PC unit) built into the
print cartridges and an image transfer unit (ITU). Each color toner is painted to its respective photoconductor at
the same time. The transfer belt passes under the four photoconductors and the four-color image is produced
and transferred to the paper in one pass.
During the printing process, the printer follows the six basic EP Process steps to create its output to the page.
These six steps are:
1.
Charge the photoconductor.
2.
Expose the photoconductor with the laser.
3.
Develop toner on the photoconductor.
4.
First transfer to the ITU, and second transfer to the paper.
5.
Fuse the toner to the paper.
6.
Clean/erase the photoconductor and the ITU.
In summary, the printer’s controller board receives print data and the command to print. The controller board
then initiates the print process. The controller board is the command center for the EP process and coordinates
the various motors and signals.
The high-voltage power supply (HVPS) sends charge to various components in the EP process. The laser fires
on the photoconductors and alters the surface charge relative to the planed image for each photoconductor.
Each photoconductor rotates past its respective developer roll, and toner is developed on the surface of each
photoconductor. The four separate color images are then transferred to the transfer belt on the ITU as it passes
under the photoconductors. After the image is transferred to the transfer belt, the photoconductors are cleaned
and recharged.
The transfer belt carries the four-colored image towards the transfer rolls. Paper is picked up from the tray and
carried to the transfer roll where the image is transferred from the transfer belt to the paper. The timing of the
paper pick is determined by the speed of the transfer belt.
The paper is carried to the fuser rollers where heat and pressure are applied to the page to permanently bond
the toner to the page. The fuser rollers push the paper into the output bin. The transfer unit is cleaned and the
process begins again for the next page.