Lexmark X 850 Owners Manual

General information1-19
7500-XXX
Fuser exit sensor
The fuser exit sensor detects the arrival of media at the detection point in the exit area of the fuser, and also 
detects the ejection of media from this point. 
Exit 
Exit 1 ejects printed media from the printer to the standard bin 1. With the exit 2 installed, it is also possible to 
eject media to the standard bin 2 by changing the orientation of the diverter gate on the exit 1. 
Dual drive motor assembly
Drives the exit 1 media exit roll assembly...

1-20MFP Service Manual 7500-XXX
Media diverter gate
The media diverter gate switches the media transport path. When the media diverter gate is lifted, media is fed to 
the standard bin exit 1. When it is lowered, media is fed to the standard bin exit 2.
Sensor (standard
bin full exit 1)Media diverter gate
Exit 1 media
exit roll asm
Dual drive
motor asm
Rear 

General information1-21
7500-XXX
Drive 
Media transport motor 
The media transport motor is a DC brushless motor that drives the exit 1 media exit shaft assembly, fuser 
assembly, registration roll assembly.
PC cartridge motor
The PC cartridge motor is a DC brushless motor that drives the PC cartridge, mag roll and transfer roll 
assembly.
Media transport
motorPC cartridge
motor Dual drive
motor
assembly
Rear
MPF/transport
motor assembly 

1-22MFP Service Manual 7500-XXX
Electrical components and controller
Switch (main power) 
Turning on/off the switch, power supplies/cuts off the main power of the printer. 
Finisher AC output
Supplies power to the finisher from the main LVPS (low voltage power supply) card assembly. 
Switch (printer front door interlock) and switch (printer left door interlock) 
The switch is a safety switch to cut off a 24 VDC power supply from the LVPS card assembly to the high volt 
power supply (HVPS) card assembly,...

General information1-23
7500-XXX
Registration roll assembly
The registration roll assembly feeds media from all trays to the PC cartridge or fuser.
Switch
(printer left door
interlock)
Fuser
cooling fan
AC drive card
assembly
Switch (printer
left lower door
interlock)
Printer engine
card asm Rear
AC power
input socket HVPS LVPS Switch (printer front
door interlock)Switch
(main power)Switch (PC
cartridge interlock)
Registration
clutch
Registration
roll assembly
Sensor (registration)
Transport
roll...

1-24MFP Service Manual 7500-XXX
Control
Media size control
Media tray assembly feeding
The following table gives the states (on/off) of the switches on the switch (media size), corresponding to the 
media sizes of the media tray assembly.
Note:  The switches on the switch (media size) are denoted by “S/W2”, “S/W4”, “S/W3”, “S/W5”, and “S/W1” 
respectively from the left side. 
Media sizeAnalog switchDigital 
switch
S/W1 S/W2 S/W3 S/W4 S/W5
 No media tray assembly Off Off Off Off Off
 5.5 X 8.5SEF/A5 SEF...

General information1-25
7500-XXX
Printhead control
Rotation of printhead motor
The on/off control of the printhead motor is performed according to the mode of operation as shown below. 
Determination of printhead ready
The printhead goes into ready state after the specified period passes since the reception of the printhead MPA 
start signal and the SOS cycle exceeds the reference value. 
Printhead reference value 
Fuser control
Fuser control method
The on/off control of the main/sub heater lamps is...

1-26MFP Service Manual 7500-XXX
Xerographic Process During a Print Cycle
Charge roll
Transfer roll
PC cartridgeFuser ASM
Magnetic roll
PaperLaser beam Heat roll
Pressure
roll
Cleaning
blade
Drum 

General information1-27
7500-XXX
Charge
The Charge Roll 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.
HVPS
(-VDC)
(-VDC)
Ground Conductive Tube Photoconductive
Surface
0V-VDC value
DRUM
Drum Surface
Voltage Drum Surface
Image
Ground
Charge roll 

1-28MFP Service Manual 7500-XXX
The charge roll is a conductive roll that is positioned slightly above the surface of the drum. The HVPS supplies 
the charge roll with two voltages; a negative DC charge voltage and an AC discharge voltage that is used for 
electrically cleaning the drum. 
Exposure
The Printhead generates a beam of laser light. Image data received from the RIP card assembly modulates this 
beam, turning it on and off according to image information that is received from the host computer...