Xerox Phaser 3250 Service Manual page 73

Theory of Operation
Thermistor (Temperature Detecting Sensor)
Thermostat (Heat Lamp Power Cut-Off)
Heat Roller
Pressure Roller
Safety Features
2-10
The Thermistor is used to detect the temperature of the heating unit and feeds
this data into the main processor.
When the Heat Lamp becomes too hot, the Thermostat cuts off power to the
Lamp to prevent from overheating.
The Heat Roller transfers heat from the Lamp to the paper. As the paper
passes between the Heat Roller and Pressure Rollers, the toner is melted and
permanently fixed to the paper. The surface of the Heat Roller is coated with
Teflon, so that toner does not stick to the surface.
The Pressure Roller, mounted under a Heat Roller, is made of a silicon resin
and the surface is also coated with Teflon. When paper passes between the
Heat Roller and the Pressure Roller, toner powder is melted and permanently
fixed to the surface of the paper.
To Prevent Overheating:
1st Protection Device: Hardware cuts off when overheated.
2nd Protection Device: Software cuts off when overheated.
3rd Protection Device: Thermostat cuts off main power to the Lamp.
Safety Device:
Fuser power is cut off when the Front Cover is opened.
Laser power is cut off when the Front Cover is opened.
The temperature of the Fuser cover's surface is maintained at less than
80° to protect the user. A Caution label is attached where the customer
can easily see when the Rear Cover is opened.
Phaser 3250 Laser Printer Service Manual