Canon LBP 2460 Service Manual - Page 59

CHAPTER 2 3. Fixing unit failure detection The CPU assumes a fixing unit failure in the following cases and reports it to the video controller. a. The rated voltage of the power supply is different to the rated voltage of the fixing roller heater. The CPU checks the POWER SUPPLY TYPE SENSE signal (PSTYPE), FIXING MAIN HEATER TYPE SENSE signal (FSRTYP1), and FIXING SUB HEATER TYPE SENSE signal (FSRTYP2) when the power is turned ON, but finds that they do not match. For example, if a 100-V power supply is connected to a 220-V fixing unit, the CPU assumes that the rated voltage does not match. b. Thermistor broken wire detection The CPU detects that the thermistor voltage is 4.6V or more when the thermistor voltage detection mode (note) is in the error detection mode, after the fixing roller heater is activated. c. Heater broken wire detection The CPU detects even after the fixing roller heater has been activated, that the FIXING MAIN HEATER CURRENT SENSE signal (/FSRCT1) and FIXING SUB HEATER CURRENT SENSE signal (/FSRCT2) are "H". d. Heater failure detection The CPU detects that the FIXING MAIN HEATER TYPE SENSE signal (/FSRCT1) and FIXING SUB HEATER TYPE SENSE signal (/FSRCT2) are "L" when the power to the fixing roller heater is interrupted. e. Maximum temperature detection The CPU detects that the thermistor detected temperature exceeds about 230°C during standby or printing. f. Warmup error detection The CPU detects this error if the fixing unit does not reach the target temperature (see table 2-2-1) within 180 seconds after warmup starts. g. Broken wire detection after the fixing unit is ready The CPU detects whether the thermistor detected temperature is 150°C or less during standby or printing. h. Relay operation detection The CPU monitors the relay detection signal (/RLDSNS) and detects that the relay has been cut by the operation of the safety circuit the power supply when the temperature of the thermistor exceeds 230°C. Note: There are two thermistor voltage detection modes: error detection mode and normal mode. In the error detection mode, sensitivity in the initial range (low temperature range) is increased to improve detection accuracy. When the thermistor temperature exceeds 60°C , it changes to the normal mode. If the CPU detects a fixing unit failure, it does the following: 1) Stops the fixing roller heater. 2) Sets the RELAY DRIVE signal (RLD) to "L", turns the relay in the power supply off to interrupt the power to the fixing roller heater. 2 - 13