Ricoh PRIPORT VT 2000 Series Service Manual page 77

28 February '91
2.10.5 Temperature Rise Detection of Thermal Head/Power Supply:
A thermistor located on the thermal head and a thermal guard located on
the power supply board are used for thermal protection. This is to prevent
the temperature of the thermal head and the power supply board from
overheating when continuously processing a solid image.
1). Thermal head detecting temp.
2). Thermal head return temp.
3). Power supply detecting temp.
When the thermistor is open, a detection signal is applied.
Thermistor
Thermal Head
Thermal Guard
PSU
1). The thermal head temperature detection signal is applied if CN404-11
becomes greater than 3.13 volts (thermal head detecting temp.-- 54
NOTE: Thermal head temperature detection signal is applied if the thermis-
tor is open circuit.
2). The thermal head temperature return signal is applied when CN404-11
becomes 2.98 volts (Thermal head return temp.-- 50
3). The thermal guard detection signal is applied if CN401-11 is 0 volt
(Power supply detecting temp.-- 85
4). The thermal guard temperature return signal is applied when CN401-11
becomes 5 volts.
5). When the temperature rise signal is applied, CN402-11 goes HIGH.
Themal
Head
Drive
CN702-13
5V CN404-13
CN702-11
CN404-11
CN404-11
CN702-20
CN401-11
54°C
50°C
85°C
+5V
Image Processing
C).
o
2-50
CN402-11
SIG: thermistor
Main Board
o C).
o C).