Panasonic UF-890 Service Manual page 245

Fuser Temperature Control Circuit
The Fuser temperature is controlled by IC51 on the LPC PC Board, which contains A/D (Analog/Digital)
converters ANI0 and ANI7. The Fuser Temperature Control Circuit uses A/D converter, ANI1. When the
PC301 drive current is transmitted from the LPC PC Board to the LVPS, the Fuser Lamp turns ON. IC55
is a converter with open output at pins 1 and 7 and is used as an abnormal temperature detection circuit.
IC55, pin 1, has a high impedance when Q602 is activated, turning ON the Fuser Lamp. An abnormal
temperature is detected when the VTH voltage level becomes higher than V+, forcing IC55, pin 1 Low
and deactivating Q602.Abnormally low and high temperatures, as well as Thermistor release status, are
detected by IC51 (CPU) programming.
CN56
1
2
Thermistor
+5v
2
nSSRA
+5v
+5v
GND
GND
GND
47
(ANI1)
IC51
CPU
Fuser Temperature Control Circuit Diagram
+5v
3
2
Q602
3
1
Q601
GND
1
GND
TP201
+24V
2 8
1
3
IC55
4
GND
nSSRA
LPC PCB
245
+24v
CN67 CN32
PC301
1
9 9
2
LVPS
6
4