Ricoh FT4215, Service Training Manual

Page: 109 / 208

11.3 FUSING LAMP CONTROL
When the main switch is turned on, the CPU starts sending a trigger pulse to
the fusing control circuit. The fusing control circuit then applies power to the
fusing lamp. The power is applied until the CPU detects the ready
temperature (175°C) through the fusing thermistor. This should take less than
60 seconds. Once the CPU detects the ready temperature, the CPU changes
the timing of the fusing lamp on/off check (checks whether the fusing lamp
should be turned on or off) from every 1 second to every 5 seconds.
During warm-up, the thermistor’s temperature lags behind the real hot roller’s
temperature. As a result, when the thermistor senses the ready temperature,
the hot roller is already at or near the operating temperature. At this time the
Ready indicator turns on.
After that, the trigger pulse is turned on constantly when thermistor detects a
temperature less than 185°C, and is turned off when the thermistor detects
186°C.
If the fusing lamp (780 W) is turned on or off when the exposure lamp is on,
the power supplied to the exposure lamp will fluctuate, possibly degrading the
copy image. To prevent this, the fusing lamp does not switch during
scanning; it stays either on or off.
Temp
Time
186°C
185°C
Ready 175°C
Room Temp
Fusing Lamp
On –
Off –
STM 2-78 FT4220/4222