Protection From Abnormal Temperatures - Konica Minolta BizHub C360 Service Manual

20. FUSING SECTION
20.3.7

Protection from abnormal temperatures

• The machine provides protection against abnormally high temperature of the fusing unit
in the following three steps.
A. First approach: thermistor protection (software)
• 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: Fusing abnormally high temperature detection (Center of the heat-
ing 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: Fusing abnormally high temperature detection (Pres-
surizing side) will be displayed.
• When the trouble code is displayed, printing will be prohibited.
B. Second approach: thermistor protection (hardware)
• 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 abnormally
high temperature detection (Center of the heating 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. Third approach: thermostat protection
• 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.
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Theory of Operation Ver. 1.0 Jul. 2009