What is a printhead?
A printhead is the part of a printer that forms the image directly on the page. Three printer types have one, and each works differently. Laser printers don't have a printhead: a laser writes the image onto a light-sensitive drum, toner sticks to the drum, and the image is transferred to the paper and fused. (LED-array printers, a close relative of the laser printer, call their light bar an LED head, but it writes on the drum and never touches the paper.)
Printheads by printer type
| Printer | How the printhead works | Typical failure |
|---|---|---|
| Inkjet | Rows of tiny nozzles fire droplets of ink, using heat (thermal inkjet) or a piezoelectric crystal | Clogged nozzles: missing lines, streaks or a missing color |
| Thermal | A row of tiny heating elements across the width of the media heats thermal paper (direct thermal) or a ribbon (thermal transfer) | Burned-out elements: thin white lines running the length of the print |
| Impact (dot matrix) | A column of pins strikes an inked ribbon against the paper | Failed pins: a white line through every row of text |
Inkjet printheads
An inkjet printhead is either built into the ink cartridge, so each new cartridge brings a fresh head, or is a semi-permanent part of the printer fed by separate cartridges or tanks. Maintenance is mostly run from the printer's software:
- Nozzle check: prints a test pattern that shows which colors have gaps.
- Head cleaning: pushes ink through the nozzles to clear clogs. It uses ink, so run a cycle or two and recheck rather than repeating it endlessly.
- Alignment or calibration: lines up the heads after a cartridge or head change. Misalignment shows as jagged lines or shadow edges.
Thermal and impact printheads
A thermal printhead is cleaned, not unclogged. With the printer off and the head cool, wipe it with isopropyl alcohol on a swab or cleaning pen to remove paper dust and adhesive that cause light or patchy print. Burned-out elements can't be cleaned; the head has to be replaced. An impact printhead gets hot during long runs and is replaced as a unit when pins fail. Replace worn ribbons promptly, since a frayed ribbon can snag the pins.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.8 covers printheads for three printer types: as an inkjet part (with cleaning printheads as maintenance), as an impact printer part you replace, and for thermal printers through cleaning the heating element. If a question asks you to clean or replace the printhead on a laser printer, it's a distractor: the matching laser parts are the drum and the toner cartridge.