HP 4550 Service Manual - Page 138

Note Overcurrent overvoltage protection Each DC power supply circuit has an overcurrent protective function and overvoltage protective function. This will prevent a power supply circuit failure by automatically interrupting the output voltage when anomalies, such as a short circuit, develop on the loads that result in overcurrent flow or abnormal voltage. If this function is activated and no DC voltage is output from the low-voltage power supply circuit, turn OFF the power switch (SW6), unplug the power cord, resolve the anomaly on the load, and then turn ON the power switch (SW6) again. Protective functions remain active for two minutes after activation. Wait for at least two minutes to turn the power back on again. High-voltage power supply The printer contains two high-voltage PCBs mounted in one assembly. Together, these PCBs generate the voltage supplied to the primary charging roller, developing sleeve, primary transfer roller, secondary transfer roller, ITB cleaning roller, and upper fusing roller. DC voltage, or superimposed AC voltage and DC voltage, is applied to the primary charging roller, developing sleeve, and ITB cleaning roller. Positive or negative DC voltage is applied to the primary transfer roller and secondary transfer roller. Negative DC voltage is applied to the upper fusing roller. 136 Theory of operation C7085-90921