2-2 Phaser 7750 Printer Service ManualSummary of the Phaser 7750 Print ProcessThe Phaser 7750 Color Laser Printer is a ‘full-color laser printer’, that utilizeselectrophotographic recording principles 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 via an intermediate transfer belt, producing full-color prints.A summary description of the printing process is presented in the following steps:1. Charging: The imaging unit charge roller is negatively charged by the High-Voltage Power Supply (HVPS) and is kept in contact with the drum surface toprovide a uniform negative charge on the drum as it rotates at a constant speed.This occurs simultaneously for YMCK.2. Exposure: The laser unit emits laser beams modulated by 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 electrostatic latent image on the drum surface. Thisprocess is performed simultaneously for YMCK.3. Development: Toner is electrostatically attracted 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 layer on the magnet roller in the developer. The magnet roller turnsagainst the surface of the drum and is kept at a constant negative potential. Atareas on the drum surface where the negative charge has not been reduced by thelaser light, potential between the drum and the toner particles is lower than thatbetween the magnet roller and the toner particles. At areas where the drumcharge has been reduced, the potential between the particles and drum is higherthan between the magnet roller and toner particles are attracted to the drum. Athin semiconductive sleeve on the magnet roller is vibrated by an AC voltage toencourage migration of the toner particles to the drum. When the toner particlesattach to the drum, the negative charge of the particles reduces drum potential atthat point, thus reducing the attraction of additional toner particles. This processis performed simultaneously for YMCK.4. Primary Transfer (Drum --> Accumulator Belt): All four toner images,formed on the individual drum surfaces, are transferred to the accumulator beltsequentially to create a complete, 4-color toner image. The accumulator belt isconductive and receives a high positive charge from the HVPS. The negativelycharged toner image on each drum surface is attracted by the high positivepotential and transfers to the accumulator belt. During this transfer, the remainingnegative charge on the drum is neutralized by the high positive charge on the belt.5. Cleaning: The drum cleaner consists of a blade and a brush in contact with thedrum after the point where the toner is transferred to the accumulator belt. Thecleaner brush receives a high positive voltage from the HVPS allowing it toelectrically attract any toner particles remaining on the drum. Toner remaining onthe accumulator belt after the image transfer to the print media is removed by thebelt cleaner assembly and transferred to the waste bin.
