Canon GP200 Service Manual page 176

3. OPERATIONS AND TIMING
4. Detecting Overheating on the
Fixing Heater End
The rear end of the fixing heater is equipped
with a sub thermistor (TH2) to check for overheat-
ing.
This is to prevent overheating and consequent
damage to the fixing film which could occur when
continuous copying is performed using copy of B4
or smaller in size. (Overheating tends to occur
where the drum is not in contact with paper.)
When the output of THE2 exceeds 250°C, the
machine increases the sheet-to-sheet distance to
accelerate heat discharge of the fixing heater,
thereby preventing overheating.
Copying operation is continued with the
increased sheet-to-sheet distance even after the
output of TH2 falls below 250°C.
If overheating continues after increasing the
sheet-to-sheet distance and the temperature
exceeds 260°C, the on-going copying operation
will be stopped and the power will be turned OFF.
(E001 will be registered.)
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COPYRIGHT © 1996 CANON INC.
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5. Protection Mechanisms
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 (TH1,
TH2); if it detects overheating of the heater
or error low temperature, it stops the power
to the heater and turns off the power. (E000
through E003 will be registered.)
2. If the error temperature detection circuit
finds that the output of TH1 is 250°C or
more or that of TH2 is 260°C for 0.2 sec or
more, the heater error detection signal
(HTNG) will be issued to turn off the relay,
stopping the power to the fixing hater and
turning off the power.
b. Thermal Fuse (FU1)
When the temperature around the thermal
fuse reaches 226 °C and the condition remains
for a specific period of time, the thermal fuse will
melt to stop the power to the fixing heater.
c. Heater ON Detection Circuit (200V model
only)
The period of time during which the fixing
heater drive signal (HTRD) remains OFF is moni-
tored; if an error is detected, the power is turned
OFF. (E004 will be registered.)
CANON GP215/200 REV.0 JULY 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)