NO PICTURE, SOUND OK. FULL BRIGHT WHITE SCREEN. NO-ON SCREEN DISPLAY
Check the video output supply voltage at Pin-1 of socket (701). It should be around 200VDC. If this voltage is absent, a white screen will be the result. This is because, all the cathodes [Rg, Rk and Rb] will get no voltage, and will get a full bright raster [Screen],which will have no effect with adjsuting Brighness or Contrast coltrols. On-screen display may be there, but the contrast to display will be very weak. Here the Screen voltage, EHT are present, but no voltages at the three cathodes of the picture tube. As emission of CRT is negatively biased, that is, as the cathod voltage go down with repect to screen voltage, the emission will increse. Here as there is no supply voltage, there will be no voltages at the three cathodes of the picture tube [Pin numbers 8, 9, & 10] of crt base socket. Measure the voltage at these pins. It should be around 155VDC. if there is no voltage, check the vidwo output supply voltage line as stated above, and find the reason, if it is absent.
Voltage to video output is derived from rectifying the voltage generated at pin number (4) of line output transformer. There is rectifier diode (D504) and a current limiting resistor (R509) [0.47Ohms/2W]. This rectifed voltage is smoothed by an electrolytic capacitor (C509), and this voltage is supplied to video output section as drive voltage to all video output transistors. If this voltage is found less than normal, or no voltage at all, the above mentioned three components should be checked. if the voltage is found very low, say 130VDC or so, the rectifier diode should be suspected. In these sections, a special types of diodes are used to rectify the voltage generated by LOT. All of them will be Fast Recovery type diodes, and the same type should be replaced. It is best to repalce the supply smoothng capacitor [33MFD 250V] along with the diode.
Contd:-
