PURPOSE: To prevent the formation of black dot defects on the fluorescent surface due to a foreign material simply and securely by radiating the laser beam from the outside of the cathode ray tube and thus removing the foreign material deposited on the aluminium film on the back side of the fluorescent surface.
CONSTITUTION: A cathode ray tube 1 whose Al film on the back side of the fluorescent surface is deposited with a foreign material is arranged on an XYZ table 2 and then the power and a deflection signal are delivered to the cathode ray tube via a circuit 3. By observing the screen of a picture tube 17 connected to a TV camera 16, the table 2 is adjusted so that the position of the foreign material will be set at the central part of the cross marked on a glass plate 14. Thereafter, the power source of the cathode ray tube 1 is disconnected and a laser beam 6 generated from a laser unit 5 containing the Nd-YAG laser 5a is radiated from the front of the cathode ray tube 1 to the centre of the foreign material. According to this method, the foreign material can be separated and removed by a part of the evaporation energy of the Al film. Thus the foreign material can be removed and the formation of the black dot defects of a cathode ray tube can be prevented in a simple manner.
KAJI TAKEO
HASEGAWA SHIYOUHEI
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