What is an impact printer?
An impact printer puts ink on paper by physically striking it. The printhead hits an inked ribbon, and the ribbon presses against the paper to leave a mark. There's no toner, no laser and no ink cartridge. The most common type is the dot matrix printer, whose printhead has a column of small pins, usually 9 or 24, that fire to build characters out of dots. Older designs such as daisy-wheel and line printers also work by impact.
Why they're still used
- Multipart forms: because the pins strike with force, they print through several layers at once, making carbon or carbonless (NCR) copies of invoices, shipping papers and receipts.
- Continuous paper: tractor feed pulls fanfold paper by the holes along its edges, so long runs of forms print without reloading.
- Tough settings and low running costs: ribbons are inexpensive, and impact printers cope with dusty warehouses and workshops.
The trade-offs are noise, slow speed and lower print quality than laser and inkjet printers.
Parts you'll service
| Part | What to know |
|---|---|
| Ribbon | The consumable that carries the ink. Faint or uneven print usually means it's dried out or worn. |
| Printhead | Holds the pins. A failed pin leaves a thin white horizontal line through every line of text. It gets hot during long jobs. |
| Head gap (platen gap) | A lever sets the distance between the head and the paper. Thick multipart forms need a wider gap; too narrow can smudge or tear the paper, too wide gives faint copies. |
| Tractor or friction feed | Tractor feed handles fanfold paper with sprocket holes; friction feed handles single sheets. |
Common problems
- Faint print: replace the ribbon, then check the head gap.
- Bottom copies too light on multipart forms: adjust the head gap, and check the form doesn't have more parts than the printer is rated for.
- A white line through each row of text: a stuck or broken pin; replace the printhead.
- Paper skewing or tearing at the holes: the tractors aren't aligned with the paper.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.8 covers impact printers: multipart paper, plus maintenance by replacing the ribbon, printhead and paper. If a question needs carbon copies or multipart forms, the answer is an impact printer. If an answer choice mentions toner for an impact printer, it's wrong.