Canon NP6012 Service Manual page 100

SSS SS SSS OF ATION S AND TIMING El
5. Checking for Overheating at the End
of the Fixing Heater
The rear end of the copier's fixing heater
is equipped with a sub thermistor (TH2) to
check for overheating.
The thermistor serves to prevent dam-
age to the fixing film otherwise caused by
overcurrent occurring in areas where paper
does not come into contact while copies are
made continuously on paper of A4 or small-
er.
In multifeeder manual mode, the copier
increases the paper-to-paper distance as soon
as the number of copies made in continuous
mode reaches a specific value indicated in the
following table, t.e., changes the copy speed
from 12 cpm to 8 cpm:
Heater temperature at | Number of copies made in
copy start continuous mode
less than 100°C ' 30th copy
100°C or more to less than 120°C
20th copy
420°C or more 10th copy
Table 3-403
By increasing the gap between sheets, the
copier decreases the power supplied to the fixing
heater, thereby preventing overheating at ends.
Once changed, the distance between
sheets of paper is maintained until copying
is over.
Should the temperature at the end of the
fixing heater still keep rising after increasing
the distance between sheets and the sub
thermistor (TH2) detects 255°C or more,
copying operation is stopped after discharg-
ing the ongoing copy; at the same time, 'H'
is indicated in the display of the contro!
panel, disabling the Copy Start key.
The 'H' indication turns off automatically
when the detection temperature of the sub
thermistor (TH2} falls below 240°C, and a
press on the Copy Start key then will make
the remaining number of copies.
Hf overheating is detected at ends, the copi-
er indicates 'H' on the control panel; advise
the user that the indication does not reter
to an error.
COPYRIGHT © 1996 CANONINC.
CANON NP6O12/ NP6012€/NP6212 REV.1 SEPT. 1995 PRINTED IN JAPAN (MPRIME AU JAPON)
6. Protection Mechanisms
The copier is equipped with the following
protection mechanisms to prevent malfunc-
tion of the fixing heater:
a. Thermistor (TH1, TH2)
The microprocessor on the DC controller
PCB monitors the voltage of the thermistor
(TH1, TH2); if it detects a high temperature
error or a low temperature error, it sends the
fixing heater error signal (HTNG) to the timer
circuit and, at the same time, indicates an
error code (E000 through E003) on the con-
trol panel. In response, the timer circuit
sends the relay off signal (RLOFF') to the
auxiliary power supply about 1.5 after it has
received the fixing heater error signal
(HTNG). The auxiliary power supply in turn
turns off the relay (RL601) to turn off the
power supply. The data for problems associ-
ated with 'E000 through E003', i.e., related
to the heater, is backed up and 'E000
through E003' will be indicated on the con-
trol panel next time the power is turned on.
When the power is turned off while
'E000' through 'E003' is indicated on the
contro! panel, 'E000 through E003' will be
indicated on the control panel if the power
switch is turned on, and the Copy Start key
will not be enabled.
b. Thermal Fuse (FU1)
If the area around the thermal fuse
exceeds 226°C and remains so for a specific
period of time, the thermal fuse melts to cut
off the power to the fixing heater.
3-55