Lexmark X 850 Owners Manual

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7500-XXX
Media transport path layout 
The following is a cross section of the laser printer, showing main components directly associated with the 
media path and transport.
Main components associated with transport of media
Duplex media
transport roll
ASM
MPF
MPF Transport
pinch roll
MPF Transport
roll ASM
Transport
roll ASM Media transport
pinch roll
Separation rollFeed roll Duplex media
center transport
roll ASM
Duplex media
transport pinch roll
Duplex media
transport roll
ASM...

1-10MFP Service Manual 7500-XXX
Functions of main components
•Media tray assembly
•Media feed unit assembly
•MPF 
•Xerographics 
•Fuser
•Drive
•Electrical components and rolls
Media tray assembly 
It is necessary to adjust the front media tray guide assembly, rear media tray guide and media tray end guide of 
the media tray assembly to match the media size. 
Front media tray guide assembly and rear media guide
The front media tray guide assembly can be adjusted to different media sizes by moving the...

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Media tray assembly
Detection of media size
The media size set for the media tray assembly is transmitted to the switch (media size) by moving these guides. 
The media size is detected by the on/off information of these switches.
Media feed unit assembly
Since tray 1 and tray 2 are functionally equivalent in terms of the switch (media size), sensor (media out), 
sensor (media level) and sensor (pre-feed), only the components of one tray are described here.
The media feed...

1-12MFP Service Manual 7500-XXX
Sensor (media level)
This sensor detects by the actuator position whether media in the media tray assembly is lifted. When the flag of 
the actuator unblocks the sensing area of the sensor (media level), the sensor detects that the media has been 
lifted.
Sensor (pre-feed)
This sensor detects a media jam in the media tray assembly by the media position and sensor on/off time.
The sensor on/off states can be monitored by media passing through the sensor (pre-feed) sensing...

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Multi-purpose feeder (MPF)
The MPF is a mechanical unit suppling media to the printer. The driving force from the transport motor of the 
dual drive motor assembly is transmitted to the MPF feed roll to feed media. 
MPF pick roll
The MPF pick roll feeds media set on the MPF and into the feeder.
MPF pick solenoid
The MPF pick solenoid transmits the driving force from the main motor to the MPF pick roll.
Sensor (MPF media out)
The sensor (MPF media out) detects whether...

1-14MFP Service Manual 7500-XXX
Detecting media size
The size of media on the MPF is transmitted by moving the MPF side guide, and is determined by the printer 
engine card assembly.
Media sizes that can be automatically detected are as follows: 
Media size Width (mm) Feed length (mm)
Side-guide stopper (min.) 84 -
Media detection area (min.) 88.2 -
3.5” x 8.5”SEF 88.9 215.9
Postcard SEF 101.6 152.4
5.5” x 8.5” SEF 139.7 215.9
Postcard LEF 148 100
A6 LEF 148 105
A5 SEF 148 210
Postcard LEF 152.4 101.6
B6...

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Registration
Sensor (registration)
The sensor (registration) must be installed before the registration roll assembly can detect whether media exists 
in the registration path.
Registration clutch
The registration clutch transmits the drive force of the main motor to the registration roll assembly.
Transport roll assembly
The transport roll assembly feeds paper from the tray 2, TTM, and optional tray to the PC cartridge and fuser.
Registration roll assembly
The...

1-16MFP Service Manual 7500-XXX
charges on the rear surface of the media. Thus, the toner image is transferred from the drum surface to the 
media surface.
Printhead assembly
The printhead scans the drum surface with a laser beam. It consists of four components: laser diode (LD) card 
assembly, printhead motor, polygon mirror, and start of scan card assembly.
1.LD card assembly – generates a laser beam with the two LDs of LD1 and LD2. The beam is turned on or 
off according to a print data signal....

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Conceptual diagram of an image created by scanning
SOS card ASM
LD card ASM
Polygon mirror
Printhead motor 

1-18MFP Service Manual 7500-XXX
Fuser
Heat roll
The heat roll is a hollow metal tube with a coated surface. This tube is heated by the inner heater lamp. The heat 
is applied to the media passing between the heat roll and pressure roll, fusing the toner on the media. 
Pressure roll
The pressure roll is a metal shaft coated with sponge rubber. Pressure is applied to the media between the 
pressure roll and heat roll, pressing the melted toner against the media.
Heater lamp
The heater rod of the lamp is...