Laser printer output relies on a combination of ground-up plastic and coloring agents, fused to the surface of paper by a heat source. Inside the printer, a drum helps apply the toner mixture to your document pages. When you understand how the drum fits into the printer's operating process and what can happen if this critical component sustains damage, you can recognize the symptoms that appear when its performance takes a hit.

Drum Location and Functions

Laser printers use a drum with a light-sensitive coating to transfer the image of a page of text and graphics onto a sheet of paper. Wherever the content of your document page should appear, a static charge makes toner stick to the drum. Some laser printers use a one-piece cartridge -- a solo consumable in a black-only printer or four cartridges in a color device -- whereas other manufacturers' designs place the drum in a separately replaceable part.

Mechanical Damage

When you prepare a new cartridge for installation into a laser printer, you remove pieces of packaging material that hold the toner supply in place and protect spring-loaded shutters from damage during shipment. Although it may be tempting to pull open a cartridge's external moving parts and peek at the drum inside, save your curiosity for experiments on the cartridge you're replacing so you can avoid damaging the new consumable. The photosensitive coating applied to the drum can sustain damage from the oils in your fingers, and even a light scratch on its surface can reduce output performance.

Light Exposure

Laser printer drum coatings respond to the light source in the device's imaging equipment. To maintain output quality throughout the life of a cartridge's toner supply, protect the drum from light exposure that doesn't involve its function as a production component. Opening the shutter once under normal office lighting for a few seconds may not damage the drum's functional performance, but prolonged light exposure, especially to bright light sources, can cause its output capability to deteriorate.

Vertical Stripes

If you see one or more thin stripes that run along the page in the direction in which the paper moves through the printer, your printer's symptoms point to a scratch around the circumference of the drum. As the drum rotates to apply a page image to a sheet of paper, toner clings to the scratch on the drum and transfers to the page as if it were part of your document content. Attempting to reuse paper that includes staples or clips provides an all-but-certain environment in which these scratches can occur. In a monochrome laser printer, these symptoms appear only in black. In a color device, these symptoms can appear in any or all of the hardware's four toner colors, including cyan, magenta, yellow and black.

Irregular Voids

Damaged areas on the drum's surface can produce corresponding blank spots on the output page. Because the drum's surface no longer functions correctly in these areas, toner no longer clings to it for transfer to paper. Although new cartridges can demonstrate these symptoms, they appear more commonly in remanufactured or refilled cartridges. In these cases, the drum may come from a used consumable that hasn't received a new light-sensitive coating, the coating may be applied incorrectly or the person who reassembles the cartridge may have touched the drum surface by accident.