HP Pro 4300 C9H70UT C9H70UT#ABA manual Fuser over-temperature protection

Fuser over-temperature protection

The fusing heater safety circuit is located on the power supply and constantly monitors the fusing temperature.

To protect the fuser from excessive temperatures, the printer has the following three protective functions:

●The CPU monitors the voltage of the thermistor. If the fuser temperature reaches 240° C (464° F) or higher, the CPU turns off the relay (RL101) to interrupt the power to the fusing heater.

●If the temperature of the fusing heater continues to rise abnormally and the temperature of the thermistor (TH1) exceeds about 250° C (482° F), the relay 1 (RL101) opens up to cut off the power supply to the fusing heater.

●When the temperature of the heater exceeds about 250° C (482° F), the thermal switch (TP1) is turned off to cut off the power supply to the fusing heater

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Figure 9.Fuser over-temperature protection circuit block diagram

72 Theory of operation Q2431-90912