Deflection Yokes are used on most computer related CRT displays. They are a set of copper coils wrapped around the neck of the Cathode Ray tube that are energized to precisely deflect the electron beam within the tube to the desired location on the monitor screen. The Deflection yoke is driven by the Vertical and Horizontal scan signals in order to "paint" the screen. The coils are actually wound around (a) ferrite core(s) and usually have center taps or multiple taps. Small magnetic tabs used to trim nonlinearities in the magnetic fields may be present attached to or mounted next to the yoke.

Early and some modern CRT's used deflection plates inside the tube to deflect the beam electrostatically rather than using deflection yokes. However, it is difficult to manufacture plates capable of strongly deflecting the high energy beams used to obtain bright pictures from modern CRTs. The greater deflection capability of deflection yokes also permits shorter tube bodies and necks than deflection plates because the beam can be deflected through greater angles. Shorter necks allow shallower monitors/TVs.

Deflection yokes are sometimes misadjusted. That causes trapezoidal and or tilted pictures. It is possible to correct those problems, but the voltages involved are quite high and very dangerous. Deflection yokes sometimes fail resulting in a distorted picture or bright line or dot instead of a picture. While it is possible to replace them, it is advisable to get a replacement with roughly the correct characteristics or the monitor may fail again with some problem such as a blown Horizontal Output Transistor or damaged flyback transformer.

Return To Index Copyright 1994-2008 by Donald Kenney.