HP LaserJet 4 Service Manual - Page 131

Conditioning Stage After the drum is physically cleaned, it must be conditioned. This process consists of applying a uniform negative charge on the surface of the drum with the primary charging roller, located in the toner cartridge. The primary charging roller is coated with conductive rubber with an AC bias applied to erase any residual charges and maintain a constant drum surface potential. In addition, a negative DC bias is applied by the charging roller to create a uniform negative potential on the drum's surface. The amount of DC voltage is modified by the print density setting from the Control Panel. Figure 5-9 Primary Charging Roller Functional Overview 5-19