The final stage view-and-release circuit plays a crucial role in amplifying the three primary colors—red (R), green (G), and blue (B)—to excite the picture tube and reproduce the color image. As illustrated in the diagram, transistors V901, V902, and V903, along with their respective bias circuits, serve as the amplifiers for the red, green, and blue primary colors. Additionally, V904, V905, diodes D904-D906, capacitors C905 and C906, and other components make up the shutdown and brightening point circuit. In particular, V905 functions as the shutdown component, while also acting as the e-pole dynamic biasing element for the discharge tubes of the R, G, and B channels.
1. The primary color amplification circuit sends the R, G, and B primary color signals from pins 50, 51, and 52 of N201 to the b poles of V901, V902, and V903 via RW01, RW02, and RW03. After amplification, these signals are then transmitted through resistors R917 and R918, R919, and sent to the CRT cathodes, stimulating the CRT to recreate the color TV image. Resistors R914, R915, and R916 act as the c-pole power supply resistors for V901, V902, and V903, respectively.
2. When the shutdown and brightening point circuit is operating normally, a 9V voltage is applied to the V905 e and b poles via R909, R910, R912, D904, and D905, turning V905 on and making it the emitter dynamic bias resistor for V901, V902, and V903. Simultaneously, the 9V voltage is added to the positive end of C906 through R913, causing C906 to charge. The charging circuit follows the path: 9V → C906 positive → C906 negative → D906 → ground, resulting in a voltage of approximately 0.3V at the e pole of V904. At this point, V904 is cut off and has no effect on the view channel. Meanwhile, another path charges C905, with its charging circuit being: 9V → C905 positive → C905 negative → R911 → ground.
At the moment of shutdown, the 9V voltage drops. Since the voltage across C905 cannot change abruptly, the negative terminal of C905 experiences a further reduction in voltage to keep V905 conducting. Similarly, because the voltage across C906 cannot change abruptly, a voltage of approximately 9V is generated at the negative terminal of C906, directly applied to the e pole of V904, thus cutting off D906 and saturating V904. The negative voltage simultaneously turns on the ec pole of V904 and R902, activating D901, D902, and D903, which in turn deeply saturates the three viewing tubes V901, V902, and V903. This causes the CRT cathode voltages to drop rapidly, leading to a quick discharge of the CRT high voltage, achieving the goal of shutting down the bright spot.
3. Other circuit descriptions include the CRT filament (HEAT) voltage input from XS902 and the accelerating pole (SCREEN) and focus voltage (FOCUS) sent from the upstream output transformer on the main board. These voltages are directly applied to the CRT header GZ01 and then sent to the CRT gun through GZ01.
In conclusion, this system ensures that the final stage view-and-release circuit efficiently manages the CRT's primary color amplification and shutdown mechanisms, allowing for seamless operation and optimal performance. The integration of various components, such as the STM32 microcontroller, industrial router crystals, and specialized capacitors, underscores the complexity and precision required in modern electronic systems. Understanding these circuits not only aids in troubleshooting but also highlights the importance of careful design and implementation in electronics engineering.
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