Heat Lamp Control Circuit - Panasonic KX-MB2230JT Service Manual

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KX-MB2230JT/ KX-MB2270JT/ KX-MB2515JT/ KX-MB2545JT/ KX-MB2575JT/ DP-MB310JT

6.16. Heat Lamp Control Circuit

The temperature of the fixing part of the Fuser Unit is converted to a Voltage by THERMISTOR and input to IC300_pinC21.
The heat lamp is turned on/off by the HTRCTL signal (IC300_pinAE22) through the photo triac (PC2) and the triac (SCR21).
Two thermostats are provided on the AC line as the safety protection devices.
Overheat protection circuit is provided so as to prevent the Fuser unit from overheating when CPU cannot control Fuser by any
problem.
IC504 compares Thermistor voltage (THRMSTR0) and predetermined voltage, which is determined by 3.3V, R581 and R584.
If Therm0 voltage becomes lower than this predetermined voltage (this voltage corresponds to about 240°C), output of
IC504_pin7 becomes "H", then Q530 turns ON.
Once Q530 turns on, IC507_pin7 keeps "H" even after the THRMSTR0 voltage becomes bigger than the voltage of IC504_pin5.
And when IC507_pin7 keeps "H", both Q500 and Q527 turn off.
As the result, once Fuser temperature exceeds 240°C (this temperature is abnormal condition), no current is supplied to Fuser lamp.
1. Heater control sequence at printing mode
a. After receiving printing data, heater turns on.
b. When heater temperature reaches to the Primary Stable Temperature (170°C).
c. When heater temperature reaches to the Secondary Stable Temperature (170°C/195°C), paper feed starts.
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