4-6. VIDEO circuit
(1) Pre-amp
<VIDEO>
The video signal from D-SUB connector is input to IC201 pre-amplifier and then clamped by clamp signal
input to pin 19. The blanking signal input to pin 27 is synthesized with the clamped signal and then output
from pins 35 (RED), 32 (GREEN) and 29 (BLUE) respectively.
V-BLK signal:Remove the raster retrace line.
H-BLK signal:Remove the side raster rolling.
<ABL>
DC voltage input to pin 15 of IC201 controls the amplitude of the video output signal. Therefore, it controls the
FBT beam current.
ABL is activated (entire white raster): Approx. 3.5VDC at pin 15
ABL is not activated (window):Approx. 4.1VDC at pin 15
The parabolic waveform is added to video output signal by synthesizing the H-DBF parabolic waveform from
Q517 and it corrects a luminance difference between the left and right side of the picture.
I2C-BUS controls D/A converter in IC201 as follows:
Contrast
Sub-brightness
R/G/B drive
OSD contrast
D/A output for the CUT-OFF circuit
(2) VIDEO-OUT and CUT-OFF circuits
The video signal input to pin 9 (RED), 8 (GREEN) and 11 (BLUE) of IC203 is amplified by 13 times and then
output from pin 3 (RED), 5 (GREEN) and 1 (BLUE) respectively.
The cut-off and brightness control voltages output from pins 23-26 of IC201 are amplified by 17 times by
IC204 and the transistor. The DC voltage output from IC203 is added to the video signal and then supplied to the
CRT cathode grid.
CRT cathode waveform
IC201 output waveform
IC201 pin 15 ABL input waveform
IC201 pin 19 clamp waveform
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ACEC
OTHERS
