Video Circuit - NEC MultiSync 3D JC-1404HME Service Manual

(2-4) Video Circuit
85V
VIDEO
SUB
UNIT VIDEO PRE-AMP,__ _ _ _ ..,
(PWE-
250I
_ _ _ _ IC901 (M51387)
CLAMP
PULSE
GAIN
CONTROL
BIAS
CONTROL
SUB BRIGHT--~
CONTROL
CONTRAST
CONTROL
I
BLANKING~
(Fig. 2-4-1) BLOCK DIAGRAM of the Video Module
G1
BRIGHTNESS
CONTROL
The video pre-amplifier consists of the pre-amp IC901 (M51387), the gain control, the bias control
circuit. the sub-brightness control circuit, and the contrast control circuit.
This pre-amplifier has two function. The first is to control the video signal output level by the gain,
the contrast. and sub-brightness controls. After the gain and the contrast controls have been adjust-
ed, the video signals output levels at the CRT cathodes are 38 Vp-p for the contrast control at the
maximum position and 10 Vp-p for the contrast control at the minimum position.
For the TTL video signal mode, the contrast control and the video pre-amp gain are fixed and can
not be adjusted.
The second function is the alignment of the cut-off for the CRT by the adjustment of the Bais
and Sub-Brightness controls. By adjusting these controls properly. the raster color will be white
for any position of the Brightness control (the Sub-Brightness control is controlled by the Bright-
ness control).
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