HP LaserJet 4 Service Manual - Page 150

Initial Rotation Period When the DC controller receives a PRINT signal (PRNT) from the formatter, the DC controller allows the fusing roller to begin warming up to approximately 183° C, and starts the main motor (M1), the pickup motor (M2), and scanner motor (M5). Next, the laser diode turns ON and generates a sweep beam used to adjust the laser power (APCIN). After the DC controller receives a BEAM DETECT signal (BD) initiated by the sweep beam, the laser power stabilizes and the sweep beam turns OFF. The DC controller then turns ON the main motor, switches the exhaust fan to high-speed rotation, applies AC high voltage and negative DC high voltage to the primary charging roller, and applies negative high voltage to the transfer roller to help remove excess toner. The developing bias (a negative AC/DC voltage) is applied to the developing roller 1.16 seconds after the main motor is turned ON, then positive high voltage is applied to the transfer roller 2.0 seconds after the main motor is turned ON. When the fusing roller temperature reaches 183°, the MP (Tray 1) pickup roller clutch solenoid (SL2) energizes and paper is fed from the tray. If paper feeds from the PC tray (Tray 2), roughly 10 seconds after Initial Rotation begins, the PC tray (Tray 2) pickup roller clutch solenoid (SL1) energizes. 5-38 Functional Overview