Drum Heater Circuit; Outline - Canon NP6251 Service Manual

CHAPTER 4 IMAGE FORMATION SYSTEM
F. Drum Heater Circuit

1. Outline

The inside of the photosensitive drum is equipped with a drum heater (60 W), and
the heater is controlled so that the surface of the drum remains a specific temperature.
The drum heater is supplied with AC power through a power switch (SW1), door
switch (SW2), and drum heater switch and by way of an AC driver.
When the drum heater switch is ON and, in addition, the door switch (SW2) is ON,
AC power is supplied regardless of the state (ON/OFF) of the power switch. When the
drum heater switch (SW3) is OFF, on the other hand, AC power is supplied to the drum
heater only if the power switch is OFF.
The drum heater drive circuit turns off when the drum heater drive signal (DHRD)
generated by the DC controller PCB goes '0', thereby supplying the drum heater with
half-wave AC power.
If the drum heater drive signal (DHRD) generated by the DC controller PCB is '1', on
the other hand, full-wave AC power is supplied to the drum heater.
The relationship between the state of the copier and the state (ON/OFF) of the drum
heater circuit of the AC driver is as follows:
Power plug connected and
power switch OFF
During copying
During standby
The temperature of the drum is monitored at all times by a thermistor (TH) built into
the drum heater.
If the surface temperature of the drum falls below a specific value, the output of the
comparison circuit goes '1', turning on the trigger circuit; as a result, the triac turns on to
turn on the drum heater.
If the surface temperature of the drum is higher than a specific value, on the other
hand, the output of the comparison circuit goes '0', turning off the drum heater.
Drum surface temperature:
Thermal fuse rated temperature: 76°C
4-22
COPYRIGHT © 1997 CANON INC.
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State of copier
Table 4-106
42°C
CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
Drum heater drive circuit
OFF
(half-wave AC power)
ON
(full-wave AC power)