Temperature Rise Detection Of Thermal Head/Power Supply - Ricoh C226 Service Manual

2.3.4 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.
1. The thermal head temperature detection signal when the voltage is
greater than 3.13 volts (thermal head detecting temp.-54°C).
NOTE: Thermal head temperature detection signal is applied if the
thermistor is open circuit.
2. The thermal head temperature return signal is applied when the voltage
drops to 2.98 volts (Thermal head return temp. -50°C).
3. The thermal guard detection signal is applied when the voltage is 0 volt
(Power supply detecting temp. -85°C).
4. The thermal guard temperature return signal is applied when the voltage
is 5 volts.
5. When the temperature rise signal is applied, the signal "SIG: Thermistor"
goes HIGH.
SM
OPTICS/IMAGE PROCESSING
54°C
50°C
85°C
2-23 C226