CertiGuide to A+ (Core Hardware)  9  Chapter 0111:  Peripheral Devices       9  VIII  Printers

VIII  Printers 1 Daisy Wheel

A dot-matrix printer works by using a print head that is made up of 9 to 24 pins. The more pins that are used the better the quality of printing can be achieved.

Each of the pins is controlled individually by an electromagnetic solenoid. Signals from the printer controller controls when each of the pins is fired.

When electromagnetic pulses are sent to a pin, the pin is forced out of the print head and impacts the printer ribbon, creating the image on paper.

The print head on dot-matrix printer can become extremely hot due to the electromagnetic nature of the solenoid. Care should be taken when servicing a dot-matrix printer as the print head can easily burn your skin.

To prevent the printer from overheating, dot-matrix printers use a thermal resistor, or thermistor, that is designed to pause or shut the printer down when it gets too hot. If this resistor goes bad the printer may constantly shut down and re-power.

The performance of a dot-matrix printer is measured in the number of characters per second (cps) it can generate. Dot-matrix printers have an advantage over their daisy wheel cousins in that they are the only type of impact printer that can produce graphic images.

VIII  Printers 1 Daisy Wheel