HP LaserJet 4v/mv Service Manual - Page 80

Figure 5-6 5PHODRM Toner Cartridge The toner cartridge is the "heart" of the Image Formation System. It houses the cleaning, conditioning, and developing steps of the process. The toner cartridge contains the photosensitive drum, primary charging roller, developing station, toner cavity, and cleaning station. Including these components that wear, degrade, or are consumed in the replaceable toner cartridge eliminates the need for a service call when replacement is required. Toner Cartridge/High Voltage Power Supply Contacts The toner cartridge has three contacts which route voltage from the HVPS PCA. They are: • Upper: Primary Charge • Middle: Developing Bias • Lower: Toner Sensing The Photosensitive Drum The special properties of the photosensitive drum allow an image to be formed on the drum surface and then transferred to paper. The drum is an aluminum cylinder. The outside of the cylinder is coated with a layer of organic-photoconductive material (OPC) which is non-toxic. The OPC material has properties similar to a photo-resistor. It becomes electrically conductive when exposed to light. When exposed to light, the negative charges deposited on the drum are conducted to the ground potential of the drum base. Areas not exposed to light remain non-conductive and maintain their negative charge. The aluminum base of the photosensitive drum is electrically connected to ground potential. Photosensitive Layer Photosensitive Drum 5-18 Functional Overview Aluminum Base