HP CM3530 Service Manual - Page 159
Fuser (fixing) over-temperature protection, Fuser (fixing)-failure detection
UPC - 884420196501
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Fuser (fixing) over-temperature protection To protect the fuser from excessive temperatures, the product has four layers of protective functions. If one function fails, the subsequent functions should detect the problem. ● DC controller: When a thermistor or thermopile detects a temperature above a certain threshold, the DC controller interrupts power to the specific heater. Following are the thresholds for each component: ◦ TH1: 230° C (446° F) or higher ◦ TH2: 285° C (545° F) or higher ◦ TH3: 285° C (545° F) or higher ● Fuser (fixing)-heater safety circuit: If the DC controller fails to interrupt the power to the heaters at the prescribed temperatures, the fuser-heater safety circuit deactivates the triac-drive circuit and releases the relay, which causes the heaters to stop at slightly higher temperature thresholds. ◦ TH2: 290° C (554° F) or higher ◦ TH3: 290° C (554° F) or higher ● Current-detection protection circuit: If current flowing in each triac exceeds a specific value, the current-detection protection circuit deactivates the triac-drive circuit and releases the relay, which interrupts the power supply to the heaters. ● 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. Breaking this contact deactivates the triac-drive circuit and releases the relay, which interrupts the power supply to the heaters. 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). Fuser (fixing)-failure detection When the DC controller detects any of the following conditions, it determines that the fuser has failed. The DC controller then interrupts power to the fuser heaters and notifies the formatter. ● 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 Or, the temperature drops in either of the thermopiles (TP1 and TP2) by 30° C (86° F) or more within a specified length of time. ENWW Engine-control system 129