Dot matrix printers are the oldest of the three technologies used in most of today’s printers - they are still common in cases when a user needs to print multi-part forms.

The dot matrix printer is an impact printer that uses a coil-fired pin to push an ink ribbon against a piece of paper - Dot matrix print heads have 9, 18 or 24 pins that are configured in a vertical line. As the printhead moves across the paper, the pins strike the ribbon against the paper.

Operation and Architecture

A dot-matrix printer can use tractor-fed paper or friction rollers to feed paper into the printer. Tractor feeds either push paper into the printer or pull paper out of the printer to move paper. In a printer using friction rollers, the feed mechanism usually pushes the paper into the printer.

As paper is fed through the printer, it runs across a flat piece of metal called a Platen - a printhead fires an array of pins into an inked ribbon that strikes the paper as it crosses the platen. The array of pins is fired at precise times to form characters or pictures on the paper.

Troubleshooting

The most common problems with dot matrix printers are mechanical problems, and a visual inspection typically provides clues to the problem. A few of the more common problems include:

Paper jams — The paper is either pushed or pulled through the paper path. If anything is obstructing the path the paper follows, the paper will jam. Make sure there is nothing applying resistance to the paper that is entering the printer, and check to be sure that the paper can be fed directly into the printer. Also, make sure no small scraps of paper are in the paper path.

Missing print — If print is missing from the page, a pin in the print head may not be firing. Look at the front of the print head and make sure the area around the pins is free of debris. Cloth from the ribbon can interfere with the firing of the pins.

Light or poor print quality — If the print head is too far from the platen, it can cause the printing to be too light. An adjustment lever at the end of the platen moves the print head closer to the platen. Poor print quality can be caused by dirt and debris in the printing area. If the print head is too close, smearing or paper jams can occur.

Paper out — If paper is installed in the printer but a “paper out� situation is indicated, check the paper out switch located near the start of the paper path. A paper jam can bend the paper switch so that the switch can’t sense that paper has been loaded in the printer.

Dark smudges — Dark smudges can appear on the paper when it is not fed through the printer fast enough. Slow paper feeding can be caused by an incorrect form thickness setting or by a tractor feed that is too tight. Adjust the tractor feed to ensure that the paper can flow smoothly through the printer.

Flecks of ink — A dirty ribbon guide can cause flecks of ink to appear on the page. Be sure the ribbon guide is clean