Specifications

C-16
PagePro25
The power from the transport motor (M2) is transmitted to the upper fusing roller so that the toner-transferred paper is fed
from the transfer section to the fusing section.
The paper is heated to melt the toner by the upper fusing roller and pressed by the upper and lower fusing rollers. The
upper fusing roller is heated by the fusing roller heater lamp (H1) which is built in it. The fusing roller thermistor (TH1) is
attached to the upper fusing roller for controlling the heater temperature. Also, the fusing roller thermostat (TH1) and fus-
ing roller heater lamp fuse (TF1) are attached to the upper fusing roller as shown on the next page. The thermostat (TH1)
and lamp fuse (TF1) are connected in series to the heater lamp (H1). The heater lamp (H1) is heated when an AC voltage
is applied.
Temperature control using the thermistor:
The resistance of the thermistor (TH1) attached to the upper fusing roller varies with temperatures. When temperature
rises, the resistance of the thermistor (TH1) decreases, and vice versa. As shown in the circuit diagram, the thermistor
output is connected to an analog port of the CPU on the main board.
The input level to the analog port of the CPU decreases as the temperature rises. The CPU performs A/D (Analog-to-Dig-
ital) conversion for the input level to know the current temperature.
To heat the upper fusing roller, the CPU set the Heater Remote 1 output to ON (“L”) state. Then, the triac on the power
supply unit turns ON and an AC voltage is applied to the fusing roller heater lamp (H1) and the upper fusing roller is
heated. The CPU monitors the output from the thermistor and controls ON/OFF of the triac to control the temperature of
the upper fusing roller.
When the upper fusing roller temperature becomes abnormal and the output from the thermistor lowers than the prede-
termined level, the abnormal-heater-temperature detecting circuit is activated and the triac is forcibly turned OFF, result-
ing in shutting off an AC voltage application to the heater lamp.
Rush current preventing circuit for heater lamp
(other model, circuit is omitted)
:
To prevent rush current when an AC voltage is applied to the heater lamp, the Heater Remote 2 signal is used. The CPU
sends this signal to the (another) triac in the form of pulse before outputting the Heater Remote 1 signal. Then, the addi-
tional resistor is connected in series to the heater lamp to suppress the rush current flowing into the heater lamp.
Thermostat (TS1) and heater lamp fuse (TF1):
If an abnormal current flows into the heater lamp because of thermistor trouble, etc. and the upper fusing roller tempera-
ture reaches about 220ûC, the contact of the thermostat automatically opens to shut off an AC voltage. (As the tempera-
ture decreases, the contact of the thermostat closes again. However, once the thermostat has been activated, it must be
replaced with new one.) When a large abnormal current suddenly flows into the heater lamp, since the thermostat cannot
respond quickly, the heater lamp fuse is blown to protect the heater lamp.
6 FUSING SECTION
Power Supply Unit
AC
Input
Abnormal Heater
Temperature
Detecting Circuit
Analog IN
CPU
Heater
Remote 1
Main Board
Thermostat
Heater Lamp Fuse
Heater Lamp
H1
Thermistor
F2
Power Switch
S1
TS1
TH1
TF1
Power Supply Unit
AC
Input
Abnormal Heater
Temperature
Detecting Circuit
Analog IN
CPU
Heater
Remote 1
Main Board
Thermostat
Heater Lamp Fuse
Heater Lamp
H1
Thermistor
F2
Power Switch
S1
TS1
TH1
TF1
Power Supply Unit
AC
Input
Power Switch
S1 F2
TS1
Main Board
Heater
Remote 1
Analog IN
CPU
TF1
H1
Heater Lamp
Heater Lamp Fuse
Thermistor
TH1
Abnormal Heater
Temperature
Detecting Circuit
Thermostat