Various Control Mechanisms; Fixing Temperature Control; Protective Functions - Canon imageCLASS MF4890dw 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.

■ 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
+24V
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
to the fixing heater.
3) Protection function by temperature fuse (TP1)
When the fixing heater temperature rises abnormally and temperature fuse (TP1)
temperature reaches approx 226 deg C, TP1 opens to shut the power supply to the fixing
heater.
● Failure detection
With this machine, 8 types of failure detection are available.
1) Initial startup failure detection
When temperature of the Fixing Assembly does not exceed 50 deg C within 1.48 sec after
the start of temperature control performed at initial rotation, it is judged as initial startup
failure.
2) Initial Thermistor open detection
When temperature of the Fixing Assembly does not exceed 35 deg C within 1.48 sec after
the start of temperature control at warm-up rotation temperature control or at cleaning
F-2-30
mode, it is judged as Thermistor open failure.
3) Short circuit of Thermistor/abnormal high temperature detection
When temperature of the Fixing Assembly is 220 deg C or higher for 30 consecutive times
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