Monday, June 20, 2011

How to check the color cathodes of a picture tube in television?

It is very easy to cehck the emission of the cathodes of a colour picture tube. Assuming all other circuit parts are working, 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 colour control to zero position.Take a wire of suitable length, say 50cms or so, tie its one end to TVs chasis [negative]. Take one resistor of value 100K 1W, tie its one end to the other end or the wire, thus one end of this resistor is now connected to negative chasis and the other end of it is free now. Hold this resistor with with some electrically noncunductive material [using hand gloves will be better]; switch on the Tv, wait a minute or so to get it warm up. Just make a touch at each cathode of the picture tube base card solderings. Just one touch will give you a colour of the respecive cathode on the screen. Never hold it for long time. This process can be used for checking cathode emission of any type of Cathode Ray Picture tubes.

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