HP LaserJet 4250 Service Manual - Page 119

Basic operation of the printer Printer operation can be divided into four systems: the control system (which includes the power supply and dc controller PCA), the pickup and feed system (which consists of various rollers and transports the media through the printer), the laser/scanner system (which forms the latent image on a photosensitive drum), and the image formation system (which transfers a toner image onto the print media). Printer operating sequence A microprocessor on the dc controller PCA controls the printer operating sequence. The table Table 5-1 Basic printer operating sequence describes the basic operating sequence from when the printer power is turned on until the final printed page is delivered to an output bin. For information about the timing of the basic operating sequence, see General timing diagrams. Table 5-1 Basic printer operating sequence Period (sequence) Waiting Standby Initial rotation Print Last rotation Description The period of time from when the printer power is turned on until the main motor (or the drum motor in the HP LaserJet 4250/4300/4350 only) begins to rotate. During this time the transfer roller is cleaned and the microprocessor on the dc controller PCA checks to determine if a print cartridge is installed in the printer. The period of time from the end of the waiting sequence or from the end of the last rotation until a print command is received from the host computer or until the printer power is turned off. The message Ready appears on the control-panel display. The period of time when the photosensitive drum is stabilized to prepare for printing. The period of time from the initial rotation until the control system detects a page entering the printer (the top of page sensor [PS103] detects the page). The period of time from the completion of the print job until the main motor (or drum motor, in an HP LaserJet 4250/4300/4350) stops. The final page of the job is delivered to an output bin and the transfer roller is cleaned. If another print job is immediately detected, then the printer returns to the initial rotation period. If no print jobs are waiting, then the printer returns to the standby period. Control system overview The control system consists of the power supply and the dc controller PCA. It controls the pickupand-feed, laser/scanner, and image-formation systems. The microprocessor on the dc controller PCA controls the printer operating sequence. When the printer power is in the standby sequence (see Table 5-1 Basic printer operating sequence), the power supply supplies direct current power (dc voltage) to the dc controller PCA. When the printer is in the standby sequence (see Table 5-1 Basic printer operating sequence) the microprocessor on the dc controller PCA sends signals to turn on and off various solenoids, motors, and other printer components that process and print the image data that the host computer sends. Introduction 105