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Picture Tilt Circuit
This circuit produces a signal that is applied to the black N/S coil sus-
pended around the plastic yoke frame by the picture tube bell. This N/S
coil serves two purposes:
1. Left or right picture tilt (rotation); and
2. Horizontal trapezoid correction.
The N/S in N/S coil stands for north/south because it compensates for the
north-south terrestrial magnetism.
Picture Tilt
The picture tilt circuit has been added to straighten the picture. The pic-
ture could have been rotated by earth's magnetic field and is no longer
parallel to the front panel.
Applying a current to a coil of wire creates a magnetic field. As an electron
beam is passed through this field, the electron beam producing the picture
will twist. The greater the current, the greater the twist. Reversing the
polarity causes the beam to turn in the opposite direction.
The picture tilt feature in this HDTV can be controlled from the user menu
and service mode. The tilt command path from the user menu to the N/S
coil is shown in the chart below:
D e v ic e
P u rp o s e
M a in
S e le c ts tilt d a ta
M ic ro
p re v io u s ly sto re d
IC 3 2 5 1
in e x te rn a l
m e m o ry .
D /A
In te rp re ts d a ta to
C o n v e rte r
m a k e a D C
IC 1 7 0 1
v o lta g e .
A m p lifie r
E x p a n d s th e 5 V
Q 1 9 0 6
in p u t ra n g e to a
+ 1 5 V ra n g e .
O u tp u t
C u rre n t d riv e
IC 1 9 0 1
N /S C o il
C h a n g e s c u rre n t
flo w in to a
m a g n e tic fie ld .
P ic tu re T ilt P a th
In
R e m o te c o n tro l
S e ria l b u s d a ta a n d
S IR C S d a ta
c lo c k IC 3 2 5 1 /p in s
IC 3 2 5 1 /p in 7
2 8 a n d 3 1 .
(n o t s h o w n )
D a ta – p in 2 1
D C v o lta g e – p in 4 .
C lo c k – p in 2 0
Q 1 9 0 6 /B a s e
Q 1 9 0 6 /C o lle c to r
D C in p u t
D C d iffe re n tia l
IC 1 9 0 1 /p in s 3
o u tp u t @ p in s 2
a n d 6 .
a n d 8 .
C N 1 9 0 1 / p in s 1
M a g n e tic fie ld
a n d 3 .
109
User Tilt Adjustment
The user has an on screen display (OSD) menu number that displays the
tilt amount from –10 to +10. The number zero should correspond to no
DC voltage entering the N/S coils if the coarse tilt adjustment in the ser-
vice mode is set correctly.
This chart shows DC circuit voltages at the three settings of the user tilt
control.
OSD
D/A Conv IC1701/pin
Tilt #
+10
2.4V
0
2.4V
-10
2.4V
Note that the D/A Converter IC1701/pin 3 voltage does not change with the
tilt settings. This is because IC1701/pin 3's voltage is used for trapezoid
correction, not tilt correction.
Service Mode Tilt Adjustment
The coarse tilt adjustment is set in the service mode. The data that corre-
sponds to the tilt voltage output at D/A Converter IC1701/pin 4 is found in:
Category DM; register #6, name = NSCO.
O u t
This information is shown this way on the TV screen in the service mode:
DM
NSCO Normal
In register #6 there are seven pieces of data, one for each of the 7 seven
picture geometry modes. The Normal 4:3 ratio picture data is shown above.
Pressing the Full, Zoom, Caption, and Wide Zoom permits you to access
the data for the four other geometry modes. The remaining two modes
apply when a HDTV picture is received in the 1080I and 480I line resolu-
tion.
In this typical set, the coarse tilt data level for a normal (4:3 ratio) width
picture is 31. This is corresponded to NO DC voltage applied to the N/S
coil when the user tilt setting is zero.
Picture Tilt Voltages
N/S Output IC1901/pin
3
4
3
4.8V
-9.48
2.4V
-9.44
0.1V
-9.41
6
31
Service
TV
6
7
Bet 2-8
-10.1V
-10.3
-7.5V
-9.3V
-9.47
0.326
-8.5V
-8.63
+7.9
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