Kyocera Mita DC-1560, Service Manual

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1AF
2-3-4
(1) Fixing unit abnormally high temperature/shorted thermistor detection circuit
CN11-25
CN11-26
H REM
CPCB
S G
S G
–
+
S
CN4-6
R96
IC20
7
6
5
TR3
65
3
R98
S
S G
S
FTH
CPU
(IC11)
I/O
(IC6)
39
H
Figure 2-3-3 Fixing unit abnormally high temperature/shorted thermistor
detection circuit
The fixing unit abnormally high temperature/shorted thermistor detection circuit forces the
fixing heater control signal H REM off if the fixing temperature reaches an abnormally high
level. This hardware safety function backs up the software-controlled shorted fixing unit
thermistor/abnormally high temperature detection feature (self-diagnostic code C64).
As the fixing temperature rises, the resistance of the fixing unit thermistor (FTH) decreases.
This increases the voltage at pin 6 of comparator IC20. When the voltage exceeds the
abnormality detection level set by resistors R96 and R98 at pin 5 of comparator IC20, the
output at pin 7 goes low, turning transistor TR3 off; this shuts off the fixing heater control
signal H REM output from pin 3 of the CPU (IC11), forcing off the fixing heater (H) controlled
via the composite PCB (CPCB).