Xerox Phaser 3425 Service Manual - Process Control
Theory of Operation
2-5
Laser Light Intensity Control
Image data is transmitted to the laser diode in the Laser Unit as digital signals. The
laser diode converts the image data from digital signals to optical signals; data
expressed by blinking laser beams. The laser unit monitors the output to determine if
variations in the light intensity from the laser beam, variations in the optical system
(such as mirrors and lenses), or variations in drum sensitivity are preventing the
system from obtaining a proper electrostatic image and, if necessary, adjusts the light
intensity to attain a stable electrostatic image.
Process Control
For stable printing, the parameters related to forming both the electrostatic and toner
image must be continuously monitored and adjusted by the printer. Parameter
correction and control over the entire printing process is called “process control”. In
the Phaser 3425 Laser Printer, the process is controlled by using feedback circuits to
monitor changes in the printing environment for each section (i.e. charging,
development, transfer, fixing, etc.) and adjusting the appropriate supply voltages to
achieve optimum printing results.
Toner Control
Print Cartridge installation and Toner Level are detected by the Print Cartridge
Interconnect Board and the associated signals are supplied to the Main Board. The
CRUM not only detects cartridge presence, it also determines whether it is a genuine
Xerox cartridge. When the toner remaining falls to 15%, the printer displays a low
toner message on the front panel display.
Fuser Control
Fuser temperature control
During fuser temperature control the printer’s target temperature is set. The heat roller
surface temperature is controlled to match the target temperature by turning the heater
lamp on/off.
The heat roller surface temperature is detected by a Thermistor. If the Thermistor
shows that the temperature is higher than the target, the heater lamp is turned off. If
the detection result is low, the heater lamp is turned on. The Fuser Control circuit
keeps the Fuser temperature at 185º C during printing and at 145º C during standby.