Panasonic BT-M1950Y Service Manual page 109

3. Side pincushion and size regulation control
Following is a somewhat more detailed description of side pincushion correction and size regulation.
The parabolic signal for correcting side pincushion distortion is produced by IC00l and goes it out from pin 11.
The parabolic signal is inverted and amplified by the IC403 opamp, amplified by IC301 and sent via 0510, 0511 and
0504 to the diode modulator. Size is regulated by controlling the center point DC of the diode modulator.
The overscan and underscan size is first selected by the overscan/-underscan signal from the MPU. This control signal
is used for the 0601 and 0603 switches. During overscan, 0601 is off and 0603 is on. Conversely, 0601 is off and
0603 is on during underscan. The DC voltage applied to IC403 pin 3 is thereby controlled (overscan: approx. 2.2 V,
underscan: approx. 3 V).
The DC voltage divided from the anode is applied as feedback to IC403 pin 3. The divided DC voltage is applied
through the IC 601 buffer (pins 5, 6 and 7) to the IC601 amplifier (pins 1, 2 and 3). The output DC voltage from IC601
pin 1 is applied through R431 to IC403 pin 3. The HVC control adjusts to prevent the IC601 offset voltage from
deviating from the specification.
IC403 amplifies the parabolic signal for side pincushion correction and controls the DC voltage for correcting size
regulation. In general, the size expands when the DC voltage decreases and compresses when the voltage increases.
OVER/UNDER
+12v
0603
FROM
1coo1@P1N
~
PARABORA
+12V
R431
Fig. 3-1 Side pincushion and size regulation control
-109-
PARABORA OUT
TO
FROM
FBT
DIODE MODULATOR
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