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EXPOSURE
3.8 LAMP HEATER CONTROL CIRCUIT
PCB1
Va
24
L. Heater ON
24
5
Vc
TH3
0/5
0
Short
GND
TH3
0/5
0
Control
TH3
0
0/5
Open
Main PCB
The lamp thermistor, which is mounted together with the lamp heater,
monitors the lamp temperature. Based on the input from this thermistor at
CN107-B1, the CPU on the main board determines whether or not to turn on
the lamp heater. To turn on the lamp heater, the main PCB drops CN107-B2
to 0 volts. This turns on SSR401 on ac controller 2, which provides ac power
to the heater.
If the exposure lamp thermistor short circuits, the comparator circuit drops
CN107-B3 to LOW. The copier then stops operation, the Call Service
Indicator (wrench mark) lights, and "E8" are alternately displayed in the Copy
Counter.
If the exposure lamp thermistor circuit becomes open, the comparator circuit
changes CN107-B4 from LOW to a 5 volt pulses. Then, service call condition
"Exposure Lamp Thermistor Open" appears. However, copying is still
possible. Refer to the "SERVICE CALL" Table.
CN107
CN407
-2
-A2
-B2
-1
CN408
-A1
-3
-2
-B3
-1
-A3
-B1
-5
-B4
-4
AC 100 V
CN401
PCB5
-2
+
~
SSR
401
~
Comparator
Circuit
AC Controller 2
2-16
31 December 1992
-1
CN406-1
H1
CN406-2
TF2
CN407-4
CN407-3
TH3
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