PURPOSE: A projection television convergence control system and a method for compensating the angle of a reference pattern are provided to compensate distortion of an image displayed on a screen due to influence of earth magnetism. CONSTITUTION: A projection television convergence control system includes a pattern generator(150), a plurality of optical sensors(S1,S2,S3,S4), and a convergence controller(140). The pattern generator generates a predetermined reference pattern. The optical sensors are set at opposite sides of a screen on which the reference pattern is displayed, to sense a variation in the luminance of the reference pattern moving on the screen. The convergence controller detects an angular error generated when the reference pattern is distorted by earth magnetism on the basis of a difference between a reference position of the reference pattern and the position of the pattern where the maximum luminance is measured by the optical sensors, and controls a deflection circuit to compensate the angular error.
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