Caple C702G Manual de servicio descargar pdf (Pagina 145)

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5. DYNAMIC FOCUS CIRCUIT

The dynamic focus circuit section is made up of following three blocks:

1) The horizontal parabolic wave generation and gain control circuit

2) The vertical parabolic wave generation and gain control circuit

3) The output amplifier circuit and the coupling circuit

1) The horizontal parabolic wave generation and gain control circuit

IC501 generates horizontal dynamic focus signal controlled by MPU data based on horizontal frequency

and horizontal screen size. The horizontal dynamic focus signal which is generated by internal logic circuit

is multiplied with vertical period signal which is created by DSP. The multiplier inside IC501 outputs the

horizontal dynamic focus signal modulated with the vertical signal. This signal is output from 8bit D/A

converter at pin 10 after it is converted to analog signal. The output signal at pin 10 is smoothed by noise

filter composed of R501 and C501. After this signal is inverted and amplified approximately 14 times by

IC513, it is sent to the horizontal dynamic focus output circuit.

R501

R50L

R50K

R50H

R50G

Noise filter

IC513

C501

3.3V

H.DF. Output

(8bit DAC)

prox. 0.5Vp-p

prox. 7Vp-p

Inverting amplifier

(Aprox.14times )

(Fig. 5.1) The horizontal parabolic wave generation and gain control circuit

2) The vertical parabolic wave generation and gain control circuit

The vertical parabolic wave is generated by DSP. IC501 generates vertical parabolic wave by calculation

based on MPU data and outputs vertical dynamic focus correction signal at IC501 pin 58. This signal is

integrated by integration circuit composed of R527 and C520. After this signal is inverted and amplified

approximately 3 times by IC510, it is sent to the vertical dynamic focus output circuit.

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Caple C702G Manual de servicio Pagina 145