Drum Heater Control - Ricoh FT8680 Service Manual

31 July 1995

2.2 DRUM HEATER CONTROL

160°C 65°C
Drum Heater
Drum Thermistor
Drum Heater 1
Drum Heater 2
The drum thermistor monitors the drum surface temperature. When the
measured temperature reaches 41°C, the main PCB determines that the
copier is ready to make copies.
When the main switch is off, the drum heater relays (RA353 and RA354) are
off, so that the drum heater is controlled by the 65°C thermoswitch. The
thermoswitch is on at 50°C and off at 65°C.
When the main switch is on, RA354 is on and bypasses the 65°C
thermoswitch from the drum heater control circuit. RA353 turns on or off
according to the temperature detected by the drum thermistor.
The drum surface temperature is controlled between 41°C and 50°C.
To minimize the power consumption, RA353 is turned on to bypass the drum
heater during the copy cycle.
Drum Thermistor
Drum
Heater 1
Drum
Heater 2
Relay PCB
2-17
DRUM
A/D
Converter
Main PCB
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