Canon NP6621 Service Manual page 145

The copier is equipped with three protection
mechanisms to prevent the fixing heater from going
ON at wrong timing.
• The microprocessor monitors the voltage of
TH1 and indicates 'E000' or 'E001' or 'E002'
or 'H003' in response to an error.
• If the voltage of TH1 and TH2 falls below
about 0.9 V (equivalent of 215°C), the error
detection circuit cuts off the supply power to
the fixing heater regardless of the output of
the microprocessor.
If the inside temperature of the thermal switch
rises above 220°C, the power to the fixing heater
will be off.
Note:
Once the contact of the thermoswitch (TS1)
opens, the thermoswitch cannot be used unless
cooled to 0°C or less; the contact will not recover
at ambient temperature.
Oil application roller
Fixing heater
(H1)
Delivery roller
Upper fixing roller
COPYRIGHT © 1998 CANON INC.
Oil application solenoid
SL6
M1
Thermistor(TH1);Main
Thermistor(TH2);Auxiliary
Thermoswitch
(220˚C)
TS1
SSR ON
Lower fixing roller
detection
Cleaning roller
Table 3-442
CANON NP6621 REV.0 FEB. 1998 PRINTED IN JAPAN (IMPRIME AU JAPON)
2. Oil Application Roller
The upper fixing roller is provided with an oil
application roller for cleaning and application of oil.
Normally, the oil application roller remains away
from the fixing roller, and it comes into contact with
the upper fixing roller only when copy paper passes
through.
The mechanism is driven by the oil application
solenoid (SL6); SL6 goes ON 1 sec after the
registration roller goes ON; it then goes OFF as
soon as the main motor (M1) goes OFF thereby
bringing the oil application roller into contact with
the upper fixing roller.
J324A-4 SL6D
Main motor
J324A- 1 TH1
-2
-3
-4
J319- 1 HTON
- 3 HTRD
SSR
Power supply
24V
J307-2 ACOFF
Relay(K1)
OPERATIONS AND TIMING
DC controller PCB
Microprocessor
(slave)
Microprocessor
(master)
Error detection
circuit
3–89