What is a laser printer?
A laser printer creates a page electrostatically. A laser draws the page as a pattern of charge on a photosensitive drum, toner sticks to that pattern, and the toner is moved onto the paper and melted in place. Toner is a dry powder of plastic resin and pigment, not ink, so laser output does not smudge once it is fused, and a failing fuser leaves toner that wipes off. Laser printers are fast, quiet and cheap per page for text, which makes them the standard office printer. Monochrome models use one black toner cartridge. Color models use four (cyan, magenta, yellow and black, or CMYK), usually laid onto a transfer belt before the image reaches the paper. Most office multifunction printers (MFPs) are laser-based.
The seven-step imaging process
Earlier A+ objectives listed the process in this order, and it is still the best way to reason about print faults:
- Processing: the printer receives the job, usually as PCL or PostScript, and its raster image processor renders the whole page into a bitmap in printer memory.
- Charging: a primary charge roller (a corona wire on older designs) puts a uniform negative charge on the drum.
- Exposing: the laser, steered by a spinning mirror, discharges the spots on the drum where toner should go. This invisible pattern is the latent image.
- Developing: the developer roller presents charged toner to the drum, and the toner sticks only to the discharged areas.
- Transferring: the transfer roller (or a transfer belt on many color models) charges the paper so it pulls the toner off the drum. A static eliminator then removes that charge so the paper does not cling to the drum.
- Fusing: the fuser assembly melts the toner into the paper with a heated roller and a pressure roller.
- Cleaning: a wiper blade scrapes leftover toner off the drum into a waste area, and the remaining charge is erased so the next rotation starts clean.
Key parts
- Toner cartridge: holds the toner. On many desktop models it also contains the imaging drum, so a new cartridge replaces the drum as well.
- Imaging drum: the photosensitive cylinder that carries the image. Do not touch its surface or leave it in bright light.
- Fuser assembly: the heat and pressure stage, running at roughly 200 °C.
- Transfer roller or transfer belt: moves toner from the drum to the paper.
- Pickup rollers and separation pads: pull one sheet at a time from the tray.
- Duplexing assembly: turns the sheet over for two-sided printing.
Maintenance
- Replace toner when the printer reports low toner or prints fade. Remove the seal or shipping tape from the new cartridge and rock it gently to spread the toner.
- Apply a maintenance kit (fuser, transfer roller, pickup rollers and separation pads) at the page count the manufacturer specifies, then reset the maintenance counter.
- Calibrate so the color layers line up and density is correct. Many color lasers do this automatically after a toner change.
- Clean paper dust and loose toner from the paper path. Power off, unplug and let the fuser cool first. Use a vacuum rated for toner on spills, because toner particles are fine enough to pass through ordinary vacuum filters.
Troubleshooting by symptom
| Symptom | Likely cause |
|---|---|
| Toner smears or rubs off | Fuser not reaching temperature, or the wrong paper type setting |
| Speckling | Loose toner inside the printer, or a leaking or damaged cartridge |
| Double or echo (ghost) images | Drum not being cleaned or erased properly, or a worn drum or fuser roller |
| Lines down the page | Scratched drum, dirty charge roller, or debris in the laser path |
| Faded prints | Low toner, toner-saver mode, a low density setting or a worn transfer roller |
| Blank pages | Seal left on a new cartridge, empty toner or a failed transfer roller |
| Jams, no pickup or multipage misfeeds | Worn pickup rollers or separation pads, or damp or wrong-weight paper |
| Garbled print | Wrong or corrupted driver, or a damaged job in the print queue |
| Grinding noise | Worn gears (often the fuser drive gear) or a foreign object |
Laser printer on the CompTIA A+ exam
Core 1 objective 3.8 lists the laser maintenance tasks: replace toner, apply maintenance kit, calibrate and clean. Objective 3.7 covers deployment, including drivers (PCL vs. PostScript), USB, Ethernet and wireless connectivity, and security settings. Objective 5.6 lists the print problems in the table above. The 220-1201 objectives do not name the seven imaging steps, but the steps are how you work out which part causes a symptom: smearing points to fusing, ghosting to cleaning or the drum, and blank pages to developing or transferring. If toner wipes off the page, think fuser. If a high-page-count printer starts jamming or shows a service message, think maintenance kit.