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Fuser Assembly The fuser assembly is almost always separate from the toner cartridge. It is usually quite easy to locate as it is close to the bottom of the toner cartridge and usually has two rollers to fuse the toner. Sometimes the fuser is somewhat enclosed and difficult to recognize because the rollers are hidden from view. To help you determine the location of the fuser, think about the data path of the paper and the fact that fusing is the final step of printing.

The toner is merely resting on top of the paper after the static charge eliminator has removed the paper’s static charge. The toner must be permanently attached to the paper to make the image permanent. Two rollers, a pressure roller and a heated roller, are used to fuse the toner to the paper. The pressure roller presses against the bottom of the page, and the heated roller presses down on the top of the page, melting the toner into the paper. The heated roller has a nonstick coating such as Teflon to prevent the toner from sticking to the heated roller.

Power Supplies All laser printers have at least two separate power supplies. The first power supply is called the primary power supply or sometimes just the power supply. This power supply, which may actually be more than one power supply, provides power to the motors that move the paper, the system electronics, the laser, and the transfer corona. The high-voltage power supply usually provides power only to the primary corona. The extremely high voltage of the high-voltage power supply makes it one of the most dangerous devices in the world of PCs! Before opening a printer to insert a new toner cartridge, it is imperative that you always turn off a laser printer!

Turning Gears A laser printer has many mechanical functions. First, the paper must be picked up. Next, the photosensitive roller must be turned and the laser, or a mirror, must be moved from left to right. The toner must be evenly distributed, and the fuser assembly must squish the toner into the paper. Finally, the paper must be kicked out of the printer and the assembly cleaned to prepare for the next page.

All of these functions are served by complex gear systems. In most laser printers, these gear systems are packed together in discrete units generically called gear packs or gearboxes. Most laser printers have two or three gearboxes that you can remove relatively easily in the rare case when one of them fails. Most gearboxes also have their own motor or solenoid to move the gears.

System Board Every laser printer contains at least one electronic board. On this board is the main processor, the printer’s ROM, and the RAM used to store the image before it is printed. Many printers divide these functions among two or three boards dispersed around the printer. An older printer may also have an extra ROM chip and/or a special slot where you can install an extra ROM chip, usually for special functions such as PostScript.

On some printer models you can upgrade the contents of these ROM chips (the firmware) by performing a process called flashing the ROM. Flashing is a lot like upgrading the system BIOS, which you learned about in Chapter 7, “BIOS and CMOS.” Upgrading the firmware can help fix bugs, add new features, or update the fonts in the printer.

Of particular importance is the printer’s RAM. When the printer doesn’t have enough RAM to store the image before it prints, you get a memory overflow problem. Also, some printers store other information in the RAM, including fonts or special commands. Adding RAM is usually a simple job—just snapping in a SIMM or DIMM stick or two—but getting the right RAM is important. Call or check the printer manufacturer’s Web site to see what type of RAM you need. Although most printer companies will happily sell you their expensive RAM, most printers can use generic DRAM like the kind you use in a PC.

Ozone Filter The coronas inside laser printers generate ozone (O3). Although not harmful to humans in small amounts, even tiny concentrations