Protective Functions; Outline; Fault Detection; External And Controls System - Canon LBP5000 Series Service Manual

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Chapter 2

4. Sheet-to-Sheet Temperature Control

The machine executes sheet-to-sheet temperature control to prevent overheating of the fixing pressure roller between sheets in continuous mode (low-speed

mode). The temperature of the fixing heater is lowered between sheets.

The sheet-to-sheet temperature, further, is varied depending on the distance between sheets and the type of paper used.

5. Throughput Reduction Control

The machine executes throughput reduction control to prevent overheating of the edges of the fixing heater during continuous printing on narrow paper.

If the reading of the sub thermistor exceeds a specific level in continuous printing, if the paper width sensor does not detect paper, or if the width of paper is less

than 195 mm, the machine will increase the distance between sheets to decrease throughput

2.6.3 Protective Functions

2.6.3.1 Outline

LBP5000 / LBP5100

The machine is equipped with the following 3 protective mechanisms to detect overheating of the fixing heater and cut power to the heater:

1. Protective Mechanism by the CPU

The CPU monitors the output voltage (MINTH, SUBTH) of the main/sub thermistor. If the voltage of MAINTH is about 0.84 V or less (equivalent of 225 deg

C or more), or if the voltage of SUBTH is about 2.12 V or more (equivalent of 245 deg C or more), the CPU will identify the condition as a fault in the fixing

assembly and execute the following:

1) The CPU stops the fixing heater drive signal (FSRD) to turn off the heater.

2) The CPU stops the relay drive signal (RLD).

3) The fixing heater safety circuit stops the main thermistor relay drive signal (RLD-).

4) The relay drive circuit opens the contact of the relay (RL901) to cut off power to the heater.

5) The machine stops printing operation, and indicates 'E001' in the status window.

2. Protective Mechanism by the Fixing Heater Safety Circuit

The fixing heater safety circuit monitors the output voltage (MAINTH, SUBTH) of the main/sub thermistor. If the voltage of MAINTH is about 0.6 V or less

(equivalent of 260 deg C or more), or if the voltage of SUBTH is about 2.8 V or more (equivalent of 270 deg C or more), the machine will identify the condition

as a fault in the fixing assembly and execute the following:

1) The fixing heater safety circuit stops the main thermistor relay drive signal (RLD-).

2) The fixing heater safety circuit stops the sub thermistor relay drive signal (RLD+).

3) The relay drive circuit turns off the relay (RL901) to cut off power to the heater.

3. Protective Mechanisms by the Thermal Fuse

The inside of the thermal fuse will melt at about 220 deg C, thereby cutting the power to the fixing heater.

2.6.3.2 Fault Detection

LBP5000 / LBP5100

The CPU will assume the presence of a fault in the fixing assembly in response to any of the forgoing conditions, and will stop the printer engine and indicate 'E001'

through 'E004' in the status window

1. Start-Up Fault (E002)

If the reading of the main thermistor is not 5 deg C or more (if at power-on, 0 deg C) 1 sec after the heater is turned on, the CPU will identify the condition as a

start-up fault.

2. Main Thermistor Error Temperature Low (E003-0000)

If the reading of the main thermistor is100 deg C (equivalent of about 2.60 V) or less continuously for 0.5 sec or more, the CPU will identify the condition as

an open circuit in the main thermistor.

3. Main Thermistor Error Temperature High (E001-000)

If the reading of the main thermistor is 225 deg C (equivalent of about 0.84 V) or more continuously for 0.5 sec or more, the CPU will identify the condition as

a main thermistor error temperature high.

4. Sub Thermistor Error Temperature Low (E001-0000)

If the reading of the sub thermistor is less than 100 deg C (equivalent of about 0.38) continuously for 0.5 sec or more, the CPU will identify the condition as a

sub thermistor error temperature low.

5. Sub Thermistor Error Temperature High (E001-0001)

If the reading of the sub thermistor is 245 deg C (equivalent of about 2.12 V) or more continuously for 0.5 sec or more, the CPU will identify the condition as a

sub thermistor error temperature high.

6. Drive Circuit Fault (E004)

If the zero-cross signal (ZEROX) is not detected for a specific period of time or more, the CPU will identify the condition as a drive circuit error.