Brother MFC-9420CN Service Manual page 66

(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.3-35)>
FLS:
THS1 / THS2:
TH:
RY:
GA/CPU:
CM1:
CM2:
CM3:
Q:
HR:
<Signal Functions>
HON-N:
ACOFF:
THERR:
AD:
Thyristor to control the on/off operation of power supply to the
heat lamp.
Thermostat to shut down the circuit for safety when it will be too
hot within the fusing unit FU.
Temperature sensor to detect the surface temperature of the heat
roller (HR).
Relay to prevent the further heating when it will be hotter than
the set point within the fusing unit FU.
Process circuit to process the temperature signal
(micro computer).
Sensor circuit for temperature signal (for ACOFF signal).
Sensor circuit for temperature signal (for HON signal).
Sensor circuit for temperature signal (for processing).
Sensor circuit for shut-down by the thermistor
(for THERR signal).
Back-up roller.
To turn on/off the heater in side the fusing roller.
To turn off the relay RY1 when it is sensed too hot.
To detect the shut-down by the thermistor.
To convert the temperature sensing signal to AD.
3 - 3 4
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