Canon LBP 2460 Service Manual - Page 58

CHAPTER 2 Table 2-2-1 WAIT STBY Cassette feed PRINT Manual feed A3/A4/B4 size Legal size Other size Target temperature (˚C) Normal temperature control Initial warm-up temperature control 170 180 169 - 177 169 - 177 190 190 185 185 180 180 190 190 b. 220V model The fixing temperature is detected by the thermistor (TH1) on the surface of the upper fixing roller. If the surface temperature rises, the TH1 resistance increases, and the voltage of the fixing roller temperature sense signal (FSRTH) decreases. Based on the FSRTH signal voltage, the microcomputer (CPU) on the DC controller outputs the FIXING MAIN HEATER DRIVE signal (/FSRDIE) and then the FIXING SUB HEATER DRIVE signal (/FSRD2E). When the FIXING MAIN HEATER DRIVE ENABLE signal (/FSRD1) or FIXING SUB HEATER DRIVE ENABLE signal (/FSRD2) is "L", the fixing roller heater drive circuit outputs the /FSRD1E or /FSRD2E signal to the fixing main heater or fixing sub heater. The CPU controls these signals according to the paper size, thickness, and pick-up source. Table 2-2-1 lists the target temperatures of the upper fixing roller during waiting, standby, and printing. 2. Protective function The printer has a mechanism that check is that the rated voltage of the power supply matches the rated voltage of the fixing main heater and the fixing sub heater to prevent the installation of a wrong fixing unit. If they do not match, the DC controller regards them as different, stops the printer and reports it to the video controller. The printer has three protection functions to prevent wrong activation of the fixing heater. • The CPU monitors the thermistor voltage. If it is abnormal, the CPU identifies the fixing unit failure, and interrupts power to the fixing unit and reports it to the video controller. • If the surface temperature of the upper fixing roller rises abnormally and the thermistor voltage falls below about 1.0V (230°C), the safety circuit in the power supply interrupts power to the fixing roller heater regardless of outputs from the CPU. • If the surface temperature of the upper fixing roller rises abnormally and the thermoswitch temperature exceeds 200°C, the thermoswitch turns off and cuts power to the fixing roller heater. 2 - 12