Fusing Lamp Circuit - Ricoh FT7770 Service Manual

30
April, '89

Fusing Lamp Circuit

6.
The resistance of TH-3 decreases as the temperature of the hot roller rises
(and vice versa).
The voltage at CN202-A4 is input to an A/D converter on the
CN202-A4.
main board, which converts these voltage changes into digital combinations
that are read by the CPU.
kilo-ohms at room temperature.)
The CPU determines hot roller surface temperature by comparing the signals
from the A/D converter with values stored in memory. Based on this com-
parison, it turns the fusing lamps on and off.
To turn on the 1,100 watt fusing lamp, the CPU supplies +3 volts at CN201-
A15 (CN201-B15 for the 550 watt lamp).
CN301-A15 (CN301-B14) to o volts.
turns on the fusing lamp.
The fusing lamp operation modes are as follows:
Warm up:
After main switch is turned on, both lamps turn on and stay on until the
temperature reaches 185°C.
Stand-by:
The 1,100 watt fusing lamp turns on at 182°C and turn off at 185ºC.
Copying Cycle:
The 1,100 watt fusing lamp turns on when the temperature drops below
182°C
Therefore, temperature changes cause voltage changes at
(The resistance of the thermistor is 119 ± 30
The ready temperature is 178ºC.
The dc drive board then drops
This energizes SSR-13 (SSR-12) which
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