Panasonic UF-5500, Service Manual

Page: 66 / 365

66
UF-5500 / 4500
6.16. Heat Lamp Control Circuit
The temperature of the fixing part of the Fuser Unit is converted to a voltage by THERMISTOR and input to IC300-D19pin. The
heat lamp is turned on/off by the HTRCTL signal (IC300-AD19pin) through the photo triac (PC2) and the triac (SCR51). And two
thermostats are set on the AC line as the safety devices.
Overheat protection circuit is provided in order to prevent the Fuser unit from overheating when CPU cannot control Fuser by
some problem.
IC504 compares Thermistor voltage and fixed voltage, which is determined by R581 and R584.
If Thermistor voltage becomes lower than this fixed voltage (this voltage corresponds to about 240 degree C), output of IC504
become "H", then Q528 turns ON, and Q500 is turned Off.
As the result, no current is supplied to Fuser lamp.
1. Control at Printing
a. After the printing signal is received, turn ON the heater.
b. After that, turn ON the motor at the Primary Stable Temperature 338
°
F (170
°
C).
c. After that, control at the Secondary Stable temperature 383
°
F (195
°
C), and feed papers.
Circuit Diagram
THERMO STAT
THERMO STAT2 AC (L)
CN1
Triac
SCR51
Photo Triac
PC2
1
2
AC (L)
AC IN
AC (N)
AC (N)
2
1
Thermistor
(PSU P.C.B)
CN101
1
CN504
HTRCTL
1
HEAT LAMP
CN508
IC300
CN53
CN52
1
3 1
THERMISTOR
SENSOR
3
+3.3V
D19
R503
C507
4
DG
THRM1
4
MAIN BOARD
LOW VOLTAGE
POWER BOARD
CN2
CN64
CN65
TONER SENSOR
1 4
AD19
4
3
R509
Over heat protection circuit
7
6
5
R579
Q528
R
577
3.3V
R535
Q500
Q527
1.2V
Q529
R596
C572
R594
R
581
R
584
Q530
R576
IC504
XSYSRST