HP 8550 Service Manual - Page 316

Power supply The side HCI power supply unit is equipped with a remote switch system. When the power switch of the copy module and printer are turned on, the printer formatter outputs a power on signal (PWRON) to the power supply PCB, to the deck controller PCB. When the PWRON signal is "1," the power supply provides +24 V and +5 V to the deck controller PCB. The lifter motor, pick-up motor, feed motor and solenoids use +24 V, while the sensors and the deck controller PCB ICs, use +5 V. A diagram of the power supply is shown below. Figure 200. Side HCI power supply Protective Functions The +24 V and +5 V power circuits are equipped with overvoltage and overcurrent protective functions that automatically turn off the output voltage to prevent the breakdown of power supply circuits in the event of overcurrent or overvoltage caused by electrical shorts or other problems on the load side. When the overvoltage and overcurrent protection functions have been triggered, and dc voltage is no longer being supplied from the power supply circuit, turn off the power switch on the copy module, and correct the problem on the load side before turning on the printer assembly power switch. 314 Chapter - 5 Theory of operation EN