User Guide

Figure 5-3 Fuser components
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)
turns off to cut off the power supply to the fusing heater.
Overcurrent/overvoltage protection
If a short-circuit or other problem on the load side causes an excessive current flow or generates
abnormal voltage, the overcurrent/overvoltage protection systems automatically cut off the output
voltage to protect the power-supply circuit.
If the overcurrent or overvoltage protection system are activated and the power-supply circuit does
not generate dc voltage, turn the power off, correct the problem, and then turn the printer on again.
The circuit has two fuses (FU1, FU2), which break and cut off the output voltage if overcurrent flows
through the alternating current (ac) line.
General descriptions 111