Canon MF4690 Service Manual - Page 91
Protection function with the fixing heater safety circuit, Protection function with the temperature
UPC - 013803076820
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T-8-4 Chapter 8 Failure of fixing assembly From the start of temperature control until 1.47 sec Normal times During normal temperature control During temperature control at sheet-to-sheet interval, during cleaning mode After the thermistor temperature exceeds 50 deg C From the start of power distribution to the fixing heater until 23 sec While a paper is nipped in the fixing assembly Thermistor temperature Less than 55 deg C 230 deg C or above Less than 100 deg C Less than 55 deg C Less than 20 deg C Less than 100 deg C Less than 210 deg C Less than 145 deg C Heater temperature detection time 0.15 sec in a row 1.2 sec in a row 1.2 sec in a row 0.3 sec in a row 30 sec in a row 30 sec in a row 2. Protection function with the fixing heater safety circuit The circuit always monitors voltage of the fixing heater temperature detection signal sent from the thermistor. If the fixing temperature greatly exceeds the specified value, it blocks the power distribution to the fixing heater regardless of the instruction from CPU. If the temperature of the fixing heater abnormally increases and the voltage of the fixing heater temperature detection signal sent from the thermistor becomes less than about 0.57V (equivalent of 265 deg C), the output of the comparator becomes 'L' and the transistor turns OFF. As a result of that, the relay is turned OFF to block the power distribution to the fixing heater regardless the relay drive signal sent from the CPU. 3. Protection function with the temperature fuse If the temperature of the fixing heater abnormally increases and the temperature of the temperature fuse exceeds about 230 deg C, the temperature fuse meltdown to block the power distribution to the fixing heater. 8-5