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FUSER UNIT
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6) Temperature detection configuration
Thermistor is a device whose resistance decreases as it detects a higher temperature. Thus its input
voltage to engine-CPU changes and then engine-CPU judges whether this change is normal or
abnormal. If one of the fuser roller thermistors is broken, the control circuit judges that the fuser
roller temperature is extremely low and keeps turning the heater lamp ON. As a result, the fuser
roller temperature rises, and possibly activates the thermostat which is a safety protection device. To
prevent this in advance, engine-CPU works to detect whether each thermistor is broken or not.
Also, the thermistors constantly check the temperature of heater lamp to prevent it from excessive
heating by LGC circuit abnormality or thermistor abnormality. The thermistors automatically turn
OFF the power when the temperature of heater lamp exceeds the specified temperature.
Fig. 13-6
138
137
PC4/AN4
PC5/AN5
Engine-CPU
Side
thermistor
Center
thermistor
+5.1V
139
PC6/AN6
+5.1V
Edge
thermistor
+5.1V
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