HP Color LaserJet CM4730 Service Manual - Page 175
Protective function by the thermoswitch, Temperature failure detection
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Protective function by the thermoswitch When the temperature of the fuser heater rises abnormally high and the detected temperature of the thermoswitch (TP) exceeds approximately 250°C (482°F), the thermoswitch is disconnected and the power supply to the fuser heater is immediately cut off. NOTE: The actual temperature of the fuser heater is about 30° higher than the thermoswitch, as the thermoswitch is not contact with the fuser heater. Temperature failure detection The CPU determines the fuser failure, stops the MFP engine, and notifies the formatter of an fuser failure when it encounters the following conditions: Start-up failure (warm-up failure) The CPU determines a start-up failure: ● If the detected temperature of the main thermistor does not reach 185°C (365°F) within 30 seconds of heater energization during the wait period. ● If the heater does not enter the Ready mode within 30 seconds of heater energization during the initial rotation period. Abnormal low temperature of main thermistor (no conduction) The CPU presumes the main thermistor has no conduction: ● If the detected temperature of the main thermistor is kept 40°C (104°F) or lower for four seconds continuously, from heater energization until the heater is turned off during the wait period. ● If the detected temperature of the main thermistor is kept 70°C (158°F) or lower for four seconds continuously, from initial rotation start until the media reaches the fuser during the initial rotation period. ● If the detected temperature of the main thermistor is kept 130°C (266°F) or lower for 0.5 seconds continuously, from when the media reaches the fuser until the heater is turned off during the print period. Abnormal high temperature of main thermistor The CPU presumes an abnormal high temperature of the main thermistor if the detected temperature of the main thermistor is kept 230°C (446°F) and higher for 0.1 seconds continuously. Abnormal low temperature of sub thermistor (no conduction) The CPU presumes the sub thermistor has no conduction: ● If the detected temperature of the sub thermistor is kept 60°C (140°F) or lower for four seconds continuously, from heater energization until the heater is turned off during the wait period. ● If the detected temperature of the main thermistor is kept 90°C (194°F) or lower for 2.5 seconds continuously, from initial rotation start until the media reaches the fuser during the initial rotation period. ENWW Engine control system 155