HP 4300 Service Manual - Page 140

Electrostatic latent-image formation Forming the electrostatic latent image on the photosensitive drum requires applying a uniform negative charge (bias) to the surface of the drum and then the exposing it to the laser beam. The laser beam naturalizes the section of the drum so that it attracts toner during the developing operation. Primary charging The conditioning process consists the primary charging roller applying a uniform negative charge on the surface of the drum. The primary charging roller is coated with conductive rubber that has an ac bias applied. This erases any residual charges and maintains a constant drum surface charge. The print density setting modifies the amount of dc voltage. Primary charging roller ac bias dc bias Photosensitive drum Figure 51. Primary charging of the photosensitive drum 120 Theory of operation Q2431-90912