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4. RASTER POSITION SWITCHING CIRCUIT
4-1. Outline
When the vertical screen position adjustment is carried out
on the projection TV, DC current is directly flown in the
vertical deflection yoke and the raster cannot be moved up
and down. (Because the raster is moved, the color distortion
may occur.) Accordingly, the vertical screen position
adjustment is carried out by the following method. (Only in
CINEMA and SUBTITLE mode)
V sync pulse output from Q501 sync. separation circuit is
once input to WAC, delayed and then output. The deflection
circuit operates with the delayed sync signal. The screen
upper side position moves up and down by varying the delay
time. When the vertical position adjustment is carried out
by WAC, the followings must be considered.
WAC becomes “through” except for CINEMA and
SUBTITLE mode.
The phase of the output V sync must not advance from that
of WAC input V sync. If it advances, Vertical jitter may occur
when performing the search operation and the vertical
position adjustment of a VTR.
Raster position
Nomal mode (4:3, Full, Dramatic Wide)
Mode in which the opposite current
flows into D
Y
(
Cinema
)
Screen
mask
position
Screen
mask
position
Fig. 8-13
So, adjust the center of the picture to the center of the screen
in advance under the output V sync delayed.
To do this, lower the raster position by flowing a DC current
to the deflection yoke in the CINEMA and SUBTITLE
mode.
The operation above is carried out by the vertical screen
position SW circuit.
4-2. Operation
When CINEMA and SUBTITLE are selected in the screen
mode, a zoom signal is input to the base of Q362 from the
autolive circuit and Q362 turns on. Then, Q363 turns off
and the base of Q364 develops H and Q364 turns on. The
inverted DC current flows into the vertical deflection yoke
from +35V power supply line.V power supply line and then
the raster moves down.
Q362
RN1204
R361
12K
Q363
2SC1815Y
Q364
2SC2023
R362
1R5.6K
R360
33K
R364
KETSU
R365
1R5.6K
R367
12K
Q365
2SC1815Y
Q367
2SC2023
R366
33K
D361
S5965G
R363
2R
220
Q366
RN1204
+35V
+12V
P360
Fig. 8-12