Canon LBP 2460 - B/W Laser Printer Service Manual page 58

CHAPTER 2
WAIT
STBY
Cassette feed
PRINT
Manual feed
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
Table 2-2-1
Normal temper-
ature control
170
169 - 177
A3/A4/B4 size 190
Legal size 185
Other size 180
190
Target temperature (˚C)
Initial warm-up temper-
ature control
180
169 - 177
190
185
180
190