Lexmark C950 Service Manual - Page 344

5058-030 The toner contained within the PC cartridge has a magnetic property that causes it to adhere to the magnet roll. The metering blade spreads the toner into a very thin layer on the magnet roll. Friction between the magnet roll and the blade generates a small electrical charge that is transferred to the toner. The surface of the magnet roll is made up of a thin sheet of conductive material. The HVPS supplies the magnet roll with two voltages: a DC voltage and an AC voltage. The DC voltage is used to transfer toner from the magnet roll to the surface of the drum. The AC voltage agitates the toner on the magnet roll, making toner transfer easier. The magnet roll maintains a negative DC electrical potential. Negatively charged areas of the drum have a lower electrical potential, or a higher relative negative value than the magnet roll. Discharged areas of the drum have a higher electrical potential, or a lower relative negative value, than the magnet roll. A discharged point on the surface of the drum now appears less negative in relation to the negative charge on the magnet roll. The toner adhering to the magnet roll is always in contact with the drum surface. When a less negative point on the drum (a discharged area) comes in contact with the more negative charged toner on the magnet roll, toner transfers from the magnet roll to that point on the drum. The toner will attract only to the area of the photoconductor drum that was exposed to the printhead LED scan line. This process would be similar to using glue to write on a can and then rolling it over glitter. The glitter sticks to the glue but won't stick to the rest of the can. There is now a visible toner image on the drum surface. The image is called a developed image. DRUM Magnetic Roll Metering Blade Toner HVPS -VDC Previous Next Go Back Drum Surface Image Drum Surface Voltage 0V Visible Developed Image Toner at -VDC Developer Bias value Discharge Level Service tips • Never touch the surface of the developer roller with your bare hand. The oil from your skin may cause a charge differential on the surface, and toner will not stick properly. The result would be repeating blotches of voids/light print on a page. To solve this, the affected cartridge must be replaced. • If the developer roller is damaged, it will not contact the surface of the photoconductor properly. The result could be repeating marks, thin vertical voids, or thin vertical lines of color on the printed page. Check the surface of the developer for damage. 3-56 Service Manual