Lexmark X925, Service Manual

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Diagnostic aids
3-29
7541-03x
Theory of operation
Printer engine
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 toner 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. We will discuss the print engine’s method of printing.
MFP electrophotographic process basics
This printer is a four LED device that uses four toner cartridges (cyan, yellow, magenta, and black) to create text
and images on media.
The printer has four photoconductors (called a photodeveloper cartridge or PC unit) and an image transfer unit
(ITU). Each color toner is painted to it’s 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 media 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 (PC unit).
2.
Expose the photoconductor (PC unit) with the LED.
3.
Develop toner on the photoconductor (PC unit).
4.
First transfer to the ITU, and second transfer to the media.
5.
Fuse the toner to the media.
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 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 roll. Media is picked up from the tray and
carried to the transfer roll where the image is transferred from the transfer belt to the media. The timing of the
paper pick is determined by the speed of the transfer belt.
The media 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 media into the output bin. The transfer unit is cleaned and the
process begins again for the next page.