| 摘要 |
PURPOSE:To obtain pictures of high contrasts by supplying the focus voltage of an optimum level to a focus voltage controller when it is used when a general broadcast screen is received and also used as a terminal display device of a computer, etc. CONSTITUTION:When a general broadcast screen is received, the focus voltage is controlled by a variable resistor VR3. Then the base voltage of a transistor TRTr1 which is applied in a reception mode of general broadcast screen is eliminated when a signal is supplied to a picture receiver from a computer. Thus the TRTr1 is turned off. Therefore a variable resistor VR4 is inserted in series to the resistor VR3. Then a CRT current raises up the focus voltage at a point C by a prescribed degree by means of the VR4. Thus the focus level is set at a point approximate to its best level. This secures pictures of high contrasts.
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