HP 4550 Service Manual - Page 137

Formatter system The formatter PCB is responsible for the following:
receiving and processing print data from the various printer interfaces
monitoring control panel inputs and relaying printer status information (through the control panel and the bidirectional I/O)
developing and coordinating data placement and timing with the print engine
storing font information
communicating with the host computer through the bidirectional interface
controlling the PowerSave mode The formatter PCB receives a print job from the bidirectional interface and separates it into image information and instructions that control the printing process. The DC controller PCB synchronizes the image formation system with the paper input and output systems, and then signals the formatter to send the print image data. The formatter PCB also provides the electrical interface and mounting locations for two EIO cards and additional memory DIMMs. CAUTION Never replace both the formatter PCB and the DC controller PCB at the same time. Doing so will result in a complete loss of data. During the removal and replacement of the formatter, data is stored in the DC controller. If the DC controller is also replaced before completing a power-on sequence, all data is lost. Control panel The formatter PCB sends and receives printer status and command data via a control panel PCB. If you replace the formatter PCB, updates will be sent to the DC controller PCB and vice-versa. Power supplies Power supply overview There are three power supplies used to power various sections of the printer. There is an AC/DC power supply and a high-voltage power supply. See Chapter 6 for instructions on accessing the power supplies. AC/DC power supply The low-voltage power supply circuit supplies +24 VDC and +5 VDC required for the printer and +3.3 VDC and +5 VDC required for the video controller. It also supplies +24 VDC for the paper pick up motor, scanner motor, and the high-voltage power supply PCB, as well as +5 VDC for the sensors and the ICs on the DC controller PCB. The front door switch or the rear door switch is deactivated by opening the drum drawer, ITB drawer, toner access cover, or delivery door. These switches are in a series and disable the +24 VDC supply when the drawers, covers, or doors are open. The low-voltage power supply circuit monitors the 5 V signal fed back from the connector PCB to ensure the 5 V power supply to the formatter. C7085-90921 Chapter 5 Theory of operation 135