Xerox Phaser 4500, Service Manual

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2-24 Phaser 4500 Service Manual
Fuser
Heat Roller The Heat Roller is a metal tube with a coated surface and a Heater
Assembly inside. As paper passes between the Heat Roller and Pressure Roller, the
heat that is applied to the paper melts the toner and fuses it to the paper.
Pressure Roller
The Pressure Roller is a metal shaft coated with sponge rubber. It
maintains pressure on the paper passing between it and the Heat Roller. This pressure
presses the melted toner against the paper.
Heater Assembly
The Heater Assembly consists of two halogen lamps located in the Heat Roller. One
lamp heats the entire length of Heat Roller, while the other, shorter rod heats the
center. The lamps are controlled by switching the neutral side of the power to each
lamp; the lamps use a common hot line.
Temperature Sensors
These are Soft Touch Sensors (STS) having a known value
of resistance that varies with temperature. There are two Temperature Sensors in the
Fuser. One is located at the center of Heat Roller, the other is located where the edge
of a letter size sheet of paper comes through. The sensors monitor the temperature of
each location to control lighting of the Heater Rods. The sensors are mounted in
contact with the surface of the Heat Roller. Power to the Heater Rod is turned on and
off using the signals from these sensors, so that the surface temperature of the Heat
Roller can be maintained within a specified range. This signal is also used to provide
a first stage of overheat protection.
Thermostats The Thermostats are connected with the Heat Roller Assembly in
series, and provide a second level of overheat protection. If the first stage of overheat
protection does not prevent the Fuser from overheating, the Thermostats cut off the
power-supply circuit for the Heater Rod. If the paper type is set incorrectly, the
Pressure Roller may melt and adhere. As a countermeasure against this, if the STS
detect the higher temperature, but can not prevent the overheat, the Thermostats cut
power to prevent the Pressure Roller from melting and adhering.
Heat Roller Fingers
These fingers peel off the leading edge of the paper from the
Heat Roller to prevent the paper from getting wound around the Heat Roller.
Heat Roller Diode The negative charge accumulated on the Heat Roller may
deteriorate the toner image on the paper during fixing. The Heat Roller Diode
discharges the charge to the frame ground.
Exit Sensor This sensor detects the arrival of the paper at a detection point in the
exit area positioned behind the Fuser. This sensor also detects the discharge of the
paper from this point. When the sensor receives light (i.e., paper is present), the signal
/EXIT is Low.