2-2 Phaser 6250 Color Laser Printer Service ManualOverview of the Phaser 6250 Color LaserPrinter Theory of OperationSummary of the Printing ProcessThe Phaser 6250 Color Laser Printer is a ‘full-color laser printer’, that utilizeselectrophotographic recording principals to place a full color image onto the printmedia. The system, contains a drum and developing unit for each color (yellow,magenta, cyan and black (YMCK)), and places the toner image of each color ontoprint media producing full-color prints through three transfer units (primary transferunits IDT1 (2 ea) and secondary transfer unit IDT2 (1 ea)).A summary description of the printing process is presented in the following Steps, seethe illustration on the following page as a reference:1. Charging: The charge roller (RTC) is negatively charged by the high voltagepower supply (HVPS) and is kept in contact with the drum surface to provide auniform negative charge on the drum as it rotates at a constant speed. This occurssimultaneously for YMCK. The refresher is a conductive brush that is alsonegatively charged by the HVPS to pick off any toner particles left on the drumafter image transfer to the IDT.2. Exposure: The laser unit emits laser beams in response to image data from theImage Processor board. The laser beams are directed onto the drum surfacethrough a system of mirrors and lenses. A rotating polygonal mirror causes thelaser beams to scan the drum surface from end to end (axially) as it rotates. Thebeams are turned on to print a pixel and off when no printing is required. Thenegative charge on the drum surface is reduced at each point where the energizedlaser beam strikes, to form an invisible electrostatic latent image on the drumsurface. This process is performed simultaneously for YMCK.3. Development: Toner is electrostatically attached to the invisible latent imageon the drum surface to form the visible image on the drum. Toner is fed into thedeveloper using the agitator and auger. The toner and the carrier in the developerform a homogeneous layer on the magnet roller in the developer. The magnetroller turns against the surface of the drum and is kept at a constant negativepotential. At areas on the drum surface where the negative charge has not beenreduced by the impact of laser light, potential between the drum and the tonerparticles is lower than that between the magnet roller and the toner particles. Atareas where the drum charge has been reduced, the potential between theparticles and drum is higher than between the magnet roller and toner particlesare attracted to the drum. A thin semiconductive sleeve on the magnet roller isvibrated by an AC voltage to encourage migration of the toner particles to thedrum. When the toner particles attach to the drum, the negative charge of theparticles reduces drum potential at that point, thus reducing the attraction ofadditional toner particles. This process is performed simultaneously for YMCK.4. Primary Transfer (drum --> IDT1): The toner image formed on the individualdrum surface is transferred onto the surface of the IDT1 (intermediate DrumTransfer 1: intermediate transfer roller 1). There are two IDT1’s: one for yellowand magenta and one for cyan and black. IDT1 is conductive and receives a highpositive charge from the HVPS. The negatively charged toner image on the drum
