Protection Function - Canon MF4100 Series Service Manual

Chapter 8
Paper length
E No object *2
F No object *2
*1: Eight modes, except envelop/small size paper
*2: When setting papers at the end of the paper guide and passing them through the machine, it becomes the small size paper mode regardless of paper length.

8.3 Protection Function

8.3.1 Protection Function
i-SENSYS MF4150 / i-SENSYS MF4140 / i-SENSYS MF4120 /
In order to prevent the fixing heater runaway, the machine has the following 3 protection functions.
1. Protection function with CPU
2. Protection function with the fixing heater safety circuit
3. Protection function with the temperature fuse
The description of each function is as follow:
1. Protection Function with CPU
CPU always monitors voltage of the fixing heater temperature detection signal sent from the thermistor. If the fixing temperature greatly exceeds the specified value,
CPU judges as failure of the fixing assembly, and it blocks the power distribution to the fixing heater.
Moreover, error (E000) is displayed in the operation part at the same time.
From the start of temperature control until 1.47 sec
Normal times
During normal temperature control
During temperature control at sheet-to-sheet interval, during cleaning mode
After the thermistor temperature exceeds 50 deg C
From the start of power distribution to the fixing heater until 23 sec
While a paper is nipped in the fixing assembly
2. Protection function with the fixing heater safety circuit
The circuit always monitors voltage of the fixing heater temperature detection signal sent from the thermistor. If the fixing temperature greatly exceeds the specified
value, it blocks the power distribution to the fixing heater regardless of the instruction from CPU.
If the temperature of the fixing heater abnormally increases and the voltage of the fixing heater temperature detection signal sent from the thermistor becomes less
than about 0.57V (equivalent of 265 deg C), the output of the comparator becomes 'L' and the transistor turns OFF. As a result of that, the relay is turned OFF to
block the power distribution to the fixing heater regardless the relay drive signal sent from the CPU.
3. Protection function with the temperature fuse
If the temperature of the fixing heater abnormally increases and the temperature of the temperature fuse exceeds about 230 deg C, the temperature fuse meltdown
to block the power distribution to the fixing heater.
8-4
PS802
E
Paper width sensor
Detect
Not detect
Failure of fixing assembly
PS804
267.4 mm
F
F-8-4
T-8-3
Delivery paper width sensor Fixing mode
Not detect Small size paper mode
Detect Small size paper mode
T-8-4
Thermistor temperature
Less than 55 deg C
230 deg C or above
Less than 100 deg C
Less than 55 deg C
Less than 20 deg C
Less than 100 deg C
Less than 210 deg C
Less than 145 deg C
Heater temperature detection time
0.15 sec in a row
1.2 sec in a row
1.2 sec in a row
0.3 sec in a row
30 sec in a row
30 sec in a row
0014-5748