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Horizontal Trapezoid Correction
In addition to tilt correction, the N/S coil also performs a mild trapezoid
(keystone) picture correction. This is controlled in the service mode as
register HTPZ #5 in the DM category. The data in the sample set is 32
during the normal, full, zoom and CC geometry modes. It is 31 in the two
DTV modes.
Correction data 32 causes D/A Converter IC1701 to output 2.4Vdc from
pin 3. This voltage is applied to the anode of zener diode D1903. As long
as the zener is forward biased, the cathode will be at 2Vdc (the zener
voltage) higher that the anode voltage. This results in a 2V addition to the
original D/A Converter voltage. The final voltage in this sample set is about
4.3Vdc and is applied to Multiplier IC1902/pin 10 for trapezoid correction
control.
Multiplier IC1902 also has a vertical sawtooth signal input at pin 11 for
trapezoid correction. The polarity and amount of sawtooth signal output is
set by a single DC voltage input IC1902/pin 10.
M u lt ip lie r I C 1 9 0 2 O u t p u t s
" D M "
C a t e g o r y
I n p u t
H T P Z
r e g is t e r
I C 1 9 0 2
# 5 D a t a
p in 1 0
3 2 ( N o r m a l)
4 . 4 4 V
0 ( M in im u m )
2 . 1 8 V
6 3 ( M a x im u m )
6 . 5 8 V
3 4 ( n o o u t p u t )
4 . 5 8 V
The signal from IC1902/pin 9 is coupled by C1905 to the N/S Output Driver
IC1901/pin 6 and 3 and added to the DC picture rotation voltage for trap-
ezoid correction.
O u t p u t – I C 1 9 0 2 / p in 9
V o lt a g e
W a v e f o r m
0 . 2 V p - p , 4 . 6 V
3 V p - p , 4 . 5 1 V
2 . 5 V p - p , 4 . 6 8 V
0 . 2 V p - p , 4 . 6 V
- - - - - - - - - - - - - - - - - - - - - - - - - -
111
Additional Components
A d d it io n a l C o m p o n e n t s
D e v ic e
Q 1 9 0 2 N o r m s w it c h
R e d u c e s t h e v e r t ic a l s ig n a l t o t h e m u lt ip lie r
I C 1 9 0 2 / p in 1 1 d u r in g n o r m a l p ic t u r e w id t h t o
in c r e a s e t h e e f f e c t iv e m u lt ip lie r I C o p e r a t in g
r a n g e .
P r e v e n t s t h e m u lt ip lie r I C 1 9 0 2 s ig n a l fr o m
D 1 9 0 5 1 6 V Z e n e r
e x c e e d in g t h e + 5 t o – 1 1 V o lt r a n g e .
D 1 9 0 1 D io d e
T e m p e r a t u r e s t a b iliz e s I C 1 9 0 1 .
P u r p o s e
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