The study and implementation of a microprocessor-controlled demagnetizer

A display monitor is constructed by a cathode ray tube (CRT), a deflection yoke (DY), and a control circuit. It is known that the shadow mask inside a color CRT could be magnetized by the earth magnetic field or other causes so as to bias the electron beam path, deviate its landing spot, and degrade the screen color purity. This paper presents an electronic demagnetizer to degauss the shadow mask and therefore improve the screen color purity. This electronic demagnetizer includes an over-current protector, a degaussing-time adjuster, and a degaussing detector to determine whether the degaussing operation is normal or not. After experiments and trials in the factory, the degaussing method presented in this paper is proved to be more effective and stable than the commercialized products off the shelf.