Ricoh FW 810 Service Manual page 37

3.8 LAMP HEATER CONTROL CIRCUIT
PCB1
Va 24
L. Heater ON 24
Vc
TH3
0/5 0
Short
GND
TH3
0/5 0
Input
TH3
0/5 0
Open
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 board 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 "E" and "8" are alternately displayed in the
Copy Counter.
If there exposure lamp thermistor circuit becomes open, the comparator circuit
changes CN107-B4 from LOW to a 5 volt pulses. The copier then stops
operation, the Call Service Indicator (wrench mark) lights, and "E" and "7" are
alternately displayed in the Copy Counter.
CN107
CN407
-A2
-B2
-A1
5
-B3
-A3
-B1
-B4
PCB5
-2
+
~
SSR
401
-1
~
CN408
-3
-2
Comparator
-1
Circuit
-5
-4
2-15
6 January 1990
AC 100 V
CN401
-2
-1
CN406-1
CN406-2
CN407-4
CN407-3
H1
TH3