GB1506749A - Apparatus for compensating misregistration of the electron beams in a colour cathode ray tube - Google Patents

Abstract

1506749 Cathode-ray-tube circuits SONY CORP 18 June 1975 [20 June 1974] 25967/75 Heading H4T Apparatus for correcting misregistration of electron beams on the colour phosphors of a colour C.R.T. due to thermal expansion and distortion of a selecting structure (e.g. shadow mask) through which the beams pass, the apparatus comprising coils 8a-8d adjacent the neck 3 of C.R.T. 1 for producing magnetic fields, a first circuit for supplying a correcting current to said coils the current varying according to the temperature of the beam selecting structure, and a second circuit for supplying a current to the coils which varies in a predetermined manner during the initial period of operation of the tube. As described, the temperature sensitive element of the first circuit comprises a thermistor 12 mounted on a printed circuit board to measure the ambient temperature of the C.R.T. and a thermistor 13 mounted on a deflection yoke 5 which is in thermal contact with the beam selecting structure. It is said that the yoke 5 does not change temperature until approximately 5 minutes after the C.R.T. is switched on, that is the change in temperature of the yoke lags behind the beam selecting structure. It is said that the electron drift D 1 after 5 minutes is half the maximum, steady value drift (Fig. 3, not shown) and the compensation due to the current in the first correcting circuit maintains the drift at D 1 . The second circuit 29 provides a current varying in a predetermined way for the first 5 minutes of operation to maintain the drift equal to D 1 , the current being passed through the coils in the opposite direction, and being reduced to 0 during the 5 minute period. The second circuit may alternatively comprise two thermistors in series (Fig. 6, not shown) whose resistance increases with time when a current flows.