HP Color LaserJet CM4730 Service Manual - Page 172

Protective functions Two fuses, FU101 and FU102, protect against overcurrent and overvoltage to prevent failures in the power supply circuit. If there is a supply error, such as a short-circuit or overvoltage, the low-voltage system automatically cuts off the output voltage. The fuses blow and cut off the AC power, once AC overcurrent flows into the AC line. If DC voltage is not being supplied from the low-voltage power supply circuit, turn off the power switch (SW101). Do not turn the power on again until the root cause is found. If the cause is not at the load side, the protective function may still work. NOTE: If the low-voltage power supply is shut down for protection, turn the power off (by switching off or unplugging the MFP) and leave the MFP off for approximately three minutes. Then turn the MFP on. Safety For safety, the +24V is divided into two: +24VA and +24VB (+24VB1 and +24VB2). The +24VA is supplied from the DC controller, whereas +24VB stops when the door switch (SW1) is cut off. The high-voltage power supply PCB and motors are supplied with the +24VB. They stop when the front cover is opened. This is to protect users and service technicians from injury. The +24VB also functions as the DOOR OPEN DETECTION signal (DOPEN). The CPU determines that the door is open when the +24VB supply stops. Sleep mode Sleep mode reduces power consumption during periods of inactivity. When the DC controller receives a Sleep command from the formatter, the controller stops the supply of +24V and +5V power by operating the power-save circuit. At the same time, it sends a POWER SAVE MODE signal (PSAVE) to the low-voltage power supply circuit. The low-voltage power supply circuit implements PSAVE upon receiving the /PSAVE signal. The MFP returns to the WAIT period once it receives a command from the formatter ending Sleep mode. Power supply recognition The low-voltage power supply circuit recognizes the voltage specification (100V or 200V) that the MFP uses and the CPU switches the temperature control firmware for the fuser accordingly. The CPU monitors the 100V POWER SUPPLY DETECTION signal (PS100V). When the MFP is connected to the 100V power source, the temperature control firmware is switched for the 100V specification. In the same way, when the MFP is connected to the 200V power source, it is switched for the 200V specification. Heater temperature control The heater temperature control detects the surface temperature of the fuser sleeve and controls the current flowing to the induction heating coil. The heater temperature control circuit is shown in Figure 4-10 Heater temperature control circuit on page 153. 152 Chapter 4 Theory of operation ENWW