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OPERATIONS AND TIMING
COPYRIGHT
©
1998 CANON INC. CANON NP6621 REV.0 FEB. 1998 PRINTED IN JAPAN (IMPRIME AU JAPON)
4. Detecting Overheating of the End of
the Fixing Heater
The rear end of the machine’s fixing heater is
equipped with a sub thermistor (TH2) to detect and
prevent overheating of the end of the fixing heater.
This consideration is made to prevent damage to
the fixing roller caused by overheating occurring as
a result of overheating on the area of the fixing not
covered by paper during copying operation, as
when making copies smaller than B5 in continuous
mode.
• If the temperature of TH2 exceeds 245°C during
the first 10 copies in continuous mode, the fixing
control target temperature is lowered by 5°C.
If the temperature still increases despite the
increase in the sheet gap and TH2 exceeds 265°C,
the ongoing copying operation is stopped and the
power will be turned OFF. At this time, ‘E001’ data
will be stored in memory.
5. Protection Mechanism
The machine is equipped with the following
protection mechanisms to prevent malfunction of
the fixing heater:
a. Thermistor (TH1, TH2)
1. The microprocessor on the DC controller
monitors the voltage of the thermistor, and if it
detects abnormally high or low temperature it
will cut off the power to the heater and will turn
OFF the machine’s power. At this time, ‘E001’
through ‘E003’ data will be stored in memory.
2. If TH1 is 260°C or more and TH2 is 270°C or
more for 0.3 sec or more, the heater error
detection signal (HTNG) of the DC controller
will turn OFF the relay (RK1) on the composite
power supply PCB to cut off the power to the
fixing heater and will turn OFF the power.
Caution:
To reset the machine, disconnect the connector
(J4) from the heater, and turn ON the power
while pressing SW850 on the service switch
PCB.
b. Thermal Fuse (FU1)
If the temperature around the thermal fuse
exceeds the fuse rating, the thermal fuse will
blow to cut off the power to the fixing heater.
c. Heater ON Detection
The heater ON detection circuit detects how
long the fixing heater drive signal (HTRD)
remains OFF and if it finds an error, it will turn
OFF the power. At this time, ‘E004’ data will be
stored in memory.