Changhong THPA88XX super single color TV shutdown shutdown bright point circuit working principle - Power Circuit - Circuit Diagram

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The final stage view and discharge circuit analyzes the role of the final stage view-and-release circuit to complete the amplification of the three primary colors of R, G, and B to excite the picture tube to reproduce the color image. As shown in the figure, V901, V902, V903 and their bias circuits form the R, G, B primary color amplifiers respectively, and V904, V905, D904~D906, C905, C906 and other components together constitute a shutdown and brightening point circuit, in which V905 is the shutdown The components of the highlight circuit are the e-pole dynamic biasing elements of the R, G, and B three-way discharge tubes.

1. The primary color amplification circuit outputs the R, G, and B primary color signals from N201 50, 51, and 52 pins to the b poles of V901, V902, and V903 via RW01, RW02, and RW03, and after amplification, respectively, through resistors R917 and R918. R919 is sent to the CRT three cathodes to stimulate the CRT to restore the color TV image. R914, R915, and R916 are c-pole power supply resistors of V901, V902, and V903, respectively.

2. When the shutdown and brightening point circuit is working normally, the 9V voltage is applied to the V905 e and b poles via R909 and R910, R912, D904 and D905 respectively, so that V905 is turned on and becomes the emitter dynamic bias resistor of V901, V902 and V903. . At the same time, the 9V voltage is added to the positive end of C906 through R913, and the C906 is charged. The charging circuit is 9V→C906 positive→C906 negative→D906→ground, so the positive end of D906 is V904 e pole voltage is about 0.3V. At this time, V904 is cut off, and does not have any influence on the view channel; the other way charges C905, and its charging circuit is 9V→C905 positive→C905 negative→R911→ground.

At the moment of shutdown, the voltage of 9V drops. Since the voltage across C905 cannot be abrupt, the voltage at the negative terminal of C905 is further reduced to maintain the conduction of V905. At the same time, because the voltage across C906 cannot be abrupt, a voltage of about 9V will be generated at the negative end of C906. , directly added to the V904 e pole, so that D906 is cut off, V904 is saturated. The negative pressure is simultaneously turned on by the ec pole and the R902 of the V904, and the D901, D902, and D903 are simultaneously turned on, and the three viewing tubes V901, V902, and V903 are simultaneously deeply saturated at the same time, the CRT three cathode voltages are rapidly lowered, and the CRT high voltage is quickly obtained. Discharge, so as to achieve the purpose of shutting down the bright spot.

3. Other circuit descriptions The CRT filament (HEAT) voltage input from the XS902 and the accelerating pole (SCREEN) and focus voltage (FOCUS) sent from the main board's upstream output transformer are directly applied to the CRT header GZ01 and sent to the CRT gun through the GZ01. .