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Theory of Operation Ver. 1.0 Sep. 2008
18.3.8
Protection from abnormally high temperature
• The machine provides protection against abnormally high temperature of the fusing unit
in the following three steps.
A. Level 1
• If the heating roller thermistor/C detects a predetermined temperature or more for more
than a predetermined period of time, the temperature is judged to be abnormally high.
Trouble code C3721: Abnormal high fusing temp. detection (center of heater side) will be
displayed.
• When the fusing pressure roller thermistor detects a predetermined temperature or more
for more than a predetermined period of time, the temperature is considered to be abnor-
mally high. Trouble code C3723: Abnormal high temp. (press side) will be displayed.
• When the trouble code is displayed, printing will be prohibited.
B. Level 2
• A different protection is provided when the CPU overruns, becoming unable to detect the
malfunction of an abnormally high temperature. If any of the thermistors detects an
abnormal temperature, the heater relay of the DC power supply is turned OFF through
the printer board. Power supply to each of the fusing heater lamps is then shut down.
• When the hardware circuit in the DC power unit detects the heater relay being OFF, the
temperature is judged to be abnormally high. Trouble code C3721: Fusing abnormal high
temperature detection (center of the heater side) will be displayed.
• Through these control procedures, the power supply to the heater lamps can be shut
down before the thermostat is activated. It thereby suppresses damage to the fusing unit
itself.
C. Level 3
• If detection of the abnormally high temperature through approaches 1 and 2 above is not
possible due to a defective thermistor or other reason, the thermostat comes into play to
shut down the power supply to each of the heater lamps.
18.3.9
Detection of a new fusing unit
• When a new fusing unit is installed in the machine, the life counter is automatically
cleared through the machine's capability of detecting a new fusing unit.
• New unit detection is made under the following situations.
The main power switch is turned ON.
The machine is reactivated from sleep mode.
18.3.10
PPM control
A. Pressure roller fusing temperature PPM control
• To achieve the intended level of fusing performance of the printed images, the printed
pages/minute value is reduced in a continuous print cycle and the machine prevents the
surface temperature of the pressure roller from decreasing.
• The print speed in a continuous print cycle varies according to the fusing temperature.
B. Small size paper PPM control
• In a continuous print cycle of small paper, to prevent the temperature on both side ends
of the fusing belt from rising, the printed pages/minute value is decreased.
• The print speed in a continuous print cycle varies according to the paper width and
length.
18.3.11
Delay control
A. Delay control for starting printing
• In order to secure the stability and to avoid the exit roller marks, timing to start feeding
paper will be delayed so that the fusing belt will be kept at the target temperature.
Y109670-2
Theory of Operation
18. Fusing section
93
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