HP CP4525DN Laser CC494A#ABA manual Failure detection

◦Current detection circuit

◦Thermoswitch

●DC controller: The DC controller monitors the detected temperature of the main thermistor and sub thermistors. The DC controller deactivates the FIXING HEATER CONTROL signal and releases the relay to interrupt power supply to the fuser heater under the following conditions:

◦TH1: 230° C (446° F) or higher

◦TH2: 285° C (545° F) or higher

◦TH3: 285° C (545° F) or higher

●Fuser-heater safety circuit: The fuser heater safety circuit monitors the detected temperature of the sub thermistors. The fuser heater safety circuit releases the relay to interrupt power supply to the fuser heater under the following conditions:

◦TH2: 290° C (554° F) or higher

◦TH3: 290° C (554° F) or higher

●Current-detection protection circuit: The current detection circuit monitors the current flowing through the fuser heater control circuit. The current detection circuit deactivates the fuser heater control circuit to interrupt power supply to the fuser heater when it detects the current higher than a specified value.

●Thermoswitch: If the temperature in the heaters is abnormally high, and the temperature in the thermoswitches exceeds a specified value, the contact to the thermoswitch breaks. Following are the thresholds for each thermoswitch:

◦TP1: 270° C (518° F) or higher

NOTE: When the thermoswitches reach this temperature, the temperature on the fuser rollers is about 320° C (608° F).

Failure detection

The DC controller determines a fuser unit failure, deactivates the FIXING HEATER CONTROL signal, releases the relay to interrupt power supply to the fuser heater, and notifies the formatter of a failure status when it encounters any of following conditions:

●Abnormally high temperatures: Temperatures are too high for any of the following components, at any time:

◦TH1: 230° C (446° F) or higher

◦TH2: 285° C (545° F) or higher

◦TH3: 285° C (545° F) or higher

●Abnormally low temperatures: Temperatures are too low at any of the following components after the product has initialized.

◦TH1: 120° C (248° F) or lower

◦TP2 or TP3: 100° C (212° F) or lower

●Abnormal temperature rise: The DC controller determines an abnormal temperature rise if the detected temperature of TH1 does not rise 2° C within a specified time after the fuser motor is

16 Chapter 1 Theory of operation ENWW