HOW TO CHECK A CRT PICTURE TUBE.
It is very easy to
check the emission of the cathodes of a color picture tube. Assuming all
other circuit functions right, including LOT [Line output Transformer]
and video output section. There is proper screen voltage; focus voltage
and EHT [Extra High Tension].
Locate the three cathode points on the base card, usually marked as Gk, Bk and Rk. Keep the brightness, contrast and color control to zero position. Take a wire of suitable length, say 50cms or so tie or clip its one end to TVs chassis [negative]. Take one resistor of value 100K 1W, tie its one end to the wire, thus one end of this resistor is now connected to negative chassis with wire and the other end of it is free now.
Hold this resistor with some electrically nonconductive material [using hand gloves will be better]; switch on the TV, wait a minute or so to get it warm up. Just make an intermittent touch at each cathode of the picture tube base card soldering.
For each intermittent touch will give you a color flash at screen of the respective cathode. For example, when you touch on the Rk cathode, will give a red color flash on the screen. Similar effect will give for the other two cathodes. If any one does not get the respective color flash on the screen, check the CRT base-connecting socket for any fault with its contacts to the picture tube pin first. Replace the CRT base socket is recommended before confirming the fault.
Never hold it for long duration of time. Only intermittent touch should be done. This process can be used for checking cathode emission of any type of Cathode Ray Picture tubes
Locate the three cathode points on the base card, usually marked as Gk, Bk and Rk. Keep the brightness, contrast and color control to zero position. Take a wire of suitable length, say 50cms or so tie or clip its one end to TVs chassis [negative]. Take one resistor of value 100K 1W, tie its one end to the wire, thus one end of this resistor is now connected to negative chassis with wire and the other end of it is free now.
Hold this resistor with some electrically nonconductive material [using hand gloves will be better]; switch on the TV, wait a minute or so to get it warm up. Just make an intermittent touch at each cathode of the picture tube base card soldering.
For each intermittent touch will give you a color flash at screen of the respective cathode. For example, when you touch on the Rk cathode, will give a red color flash on the screen. Similar effect will give for the other two cathodes. If any one does not get the respective color flash on the screen, check the CRT base-connecting socket for any fault with its contacts to the picture tube pin first. Replace the CRT base socket is recommended before confirming the fault.
Never hold it for long duration of time. Only intermittent touch should be done. This process can be used for checking cathode emission of any type of Cathode Ray Picture tubes
