Various Control Mechanisms; Fixing Temperature Control; Protective Functions - Canon MF4500 Series Service Manual

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Technical Overview > Fixing System > Various Control Mechanisms > Protective Functions

Various Control Mechanisms

■ Fixing Temperature Control

● Heater Temperature Control
The heater temperature control is to keep the fixing heater in the fixing film unit to the
specified temperature.
The engine controller monitors the fixing heater temperature detection signal (FSRTH) and
outputs the fixing heater drive signal (FSRD) according to the detected temperature.
The fixing heater drive PCB controls the fixing heater according to this signal to keep the
fixing heater temperature within the target values.
Engine controller
Low-voltage
power supply
CPU
Frequency
FREQSNS
detection
circuit
(220-240V model only)
FSRD
24VOFF
FSRTH
Fixing heater (H1)
Thermistor (TH1)
Pressure
roller
Fixing film
Thermal fuse (TP1)
2 Technical Overview > Fixing System > Various Control Mechanisms > Protective Functions
Fixing control
Relay drive
FU101
circuit
RL101
Fixing heater
safety circuit
Fixing heater
drive circuit
There are 11 types of target fixing temperature depending on the fixing mode.
These types are according to the paper type settings and resolution settings on a driver.
The number of sheets Normal Heavy1 Heavy2 Light OHT Envelope Envelope2 Quiet
1
2 to 6
7 to 26
27 to 41
42 to 76
77 to 150
151 to 197
More than 198
The number of sheets Post
+24V
1
2 to 6
7 to 26
27 to 41
42 to 76
77 to 150
151 to 197
More than 198

■ Protective Functions

● Protective Function of fixing assembly
Host machine carries the following 3 functions to prevent the fixing heater from overheating.
1) Protective function by CPU
CPU of engine controller monitors the thermistor (TH1) temperature consistently.
When TH1 reaches approx 220 deg C, CPU determines that the fixing heater is overheating
and stops the fixing heater drive signal (FSRD) output and also turns OFF relays to shut
the power supply to fixing heater.
2) Protection function by fixing heater safety circuit
F-2-31
Fixing heater safety circuit monitors the thermistor (TH1) temperature consistently.
When TH1 reaches approx 235 deg C, it determines that the fixing heater is overheating
and the fixing heater safety circuit turns OFF the relay drive circuit to shut the power supply
fixing mode
185 175 185 160 165 165
185 175 185 160 165 165
185 175 185 160 165 165
185 175 185 160 165 165
185 173 185 160 165 165
183 170 185 160 165 165
180 170 185 160 165 165
180 170 185 160 165 165
fixing mode
Nomal Nomal
N/N (Copy)
185 185 190
185 185 190
185 185 190
185 185 190
185 185 190
185 183 188
185 180 185
185 180 185
2-23
145 150
143 150
140 150
140 150
138 148
135 145
135 145
135 145
T-2-6
T-2-7
2-23