An imaging drum is a consumable part in a laser or LED page printer. Although every laser printer has one, some package the imaging drum in the toner cartridge, while others separate the drum from the toner, like the Samsung CLX-3170 toner printer. These printers typically have lower toner costs, and can usually get a few toner cartridges' worth of life from the drum.
The imaging drum itself is a cylinder coated with a photosensitive chemical. The laser or LED array in the printer flashes the image of the page onto the drum as it rotates. Areas of the drum that get struck by light take on a strong electrical charge. After being hit by the light, the drum then gets rotated through the toner supply. The toner carries an opposite charge to the drum, and gets attached to the charged areas of the drum. After picking up the toner, the drum then rotates to the even more strongly charged paper that pulls the toner off of the drum. The toner-coated paper then passes through a fuser that melts the toner onto it, and comes out of the printer as a printed document.
Printers that contain an imaging drum in their toner cartridge assembly, such as black and white Hewlett-Packard LaserJets, have their imaging drum replaced every time that the toner cartridge gets replaced. Other printers, such as Okidata and Brother laser printers as well as many color LaserJet printers, have a separate imaging drum. These printers will typically let the user know when their drum needs to be replaced.
Drum lives vary widely from printer to printer, although they typically run into the thousands, if not tens of thousands, of pages. One major variable in their life is how much they actually print. While a drum will last a long time if it is used to print lightly-covered black and white pages, pages with a high degree of coverage of multiple colors can burn up drums relatively quickly.
Regardless of whether the printer indicates that the drum needs replacement, if a printer is having print quality issues, a new drum may be necessary. Drums can fail due to having their surface damaged or due to being exposed to too much light. If a printer continually makes prints with scratches, spots, blotches, or faded areas and its toner cartridges are full, it may have a drum that needs replacement.
The specific procedure to replace a drum varies from printer to printer. However, it typically requires that the front panel be opened and the main toner cartridge be removed. After that, the drum typically can be slid or lifted out and replaced with a new one. Some color printers allow the drum to be replaced without removing any of the cartridges. In any case, the printer's manual or control panel typically walks users through the process.