Brother HL-3450CN Series, Service Manual

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CHAPTER 4 STRUCTURE OF SYSTEM COMPONENTS
4-40
(3) Control of the Fusing Temperature
Each roller of the fusing unit is controlled to maintain the appropriate temperature so
that toner will be fixed correctly onto the print paper.
<Basic Structure of Temperature Control (Fig.4-36)>
FLS: Thyristor to switch the power supply to the heat lamp.
TFU1/TFU2: Temperature fuse to shut down the circuit for safety when the
temperature becomes too hot within the fixing unit.
TH: Temperature sensor to detect the surface temperature of the
heat roller (HR).
RY: Relay to prevent further heating when it becomes hotter than
the set temperature within the fixing unit.
GA/CPU: Process circuit to control the temperature signal (micro
computer).
CM1: Sensor circuit for temperature signal (for ACOFF signal).
CM2: Sensor circuit for temperature signal (for HON signal).
CM3: Sensor circuit for temperature signal (for processing).
Q: Sensor circuit for shut-down by the thermistor (for THERR
signal).
HR: Heat lamp for the heat roller.
BR: Heat lamp for the back-up roller.
< Signal Functions >
HON-N To turn on/off the heater inside the fuser roller.
ACOFF To turn off the relay RY1 if overheat occurs.
THERR To detect the shut-down by the thermistor.
AD To convert the temperature sensing signal to AD.
<Controlled Temperature and Safety>
150 TS
TA
TPS
Time
Temperature
( )
C
C
Fig. 4-35