2-4. V Linearity Characteristic Correction

2-4-1. S-character Correction

(Up-and Down-ward Extension Correction)

A parabola component developed across C306 is integrated by R306 and C305, and the voltage is applied to pin 6 of Q302 to perform S-character correction.

2-4-2. Up-and Down-ward Linearity Balance

A voltage developed at pin 2 of Q301 is divided with resistors R307 and R303, and the voltage is applied to pin 6 of Q301 to improve the linearity balance characteristic.

3. PROTECTION CIRCUIT FOR V DEFLECTION STOP

Q301

2

L462+L463+L464

C306

Q350

 

R352

12V 9V

 

D350

 

 

 

 

 

R351

 

R354

 

 

Q351

 

BLANKING

C350

D354

CIRCUIT

 

 

 

R305

R350

Q353

D353

Fig. 8-9

When the deflection current is not supplied to the deflection coils, one horizontal line appears on the screen. If this condition is not continued for a long time, no trouble will occur in a conventional TV. But in the projection TV, all the electron beams are directly concentrated at the fluorescent screen because of no shadow mask used, and burns out the screen instantly.

To prevent this, the stop of the V deflection is detected when the horizontal one line occurs, and the video signals are blanked out so that the electron beams are not emitted.

When the V deflection circuit is operating normally, a sawtooth wave voltage is obtained across (R305), so Q350 repeats on-off operation in cycle of V sync. In this case, the collector voltage of Q35 is set to develop less than (12V- VBE (Q351)) with R352 and C350 as shown in Fig. 8-9. Accordingly, Q351 and Q353 are continuously turned on. As a result, diode D354 is turned off, giving no influence on the blanking operation.

Next, when the V deflection stops, the voltage across (R305) does not develop, so Q350 turns off, and both the Q351 and Q353 are turned off. Then, the picture blanking terminal pin 13 of ICA05 is set to high through R354 and D354 connected to 90V power line, BLANKING CIRCUIT ON thus cutting off the projection tubes.

Volttage Across

R305

Q350 BASE

Q340 VBE

12V-VBE(Q341)

Q351 Collector

Fig. 8-10

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Toshiba TW40F80 manual Protection Circuit for V Deflection Stop, Linearity Characteristic Correction