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•
Period t1-t2: When TS7421 is driven into conductivity, the
capacitor voltage of 141 V will be divided across bridge-coil
L5422 and the deflection coil (connector 1417). Due to the
chosen inductance values, there will be 100 V across the
deflection coil and 41 V across L5422. The linear
increasing current in the deflection coil will result in a spot
moving from the centre of the picture tube to the right. The
voltage across L5422 will also charge C2421 (41 V - 0.7 V).
•
Period t2-t3: At the moment the LINEDRIVE signal
becomes high, TS7421 will stop conducting. In the coils a
voltage will be induced, trying to maintain the current. The
current through the line deflection coils continues to flow
through C2425 and C2421 and the current through L5422
continues to flow through C2426 and C2421. The energy
stored in the line deflection coil is passed to C2425, and the
energy of L5422 to C2426. The resonance-frequencies of
these two LC-circuits define the flyback time of the spot
from the right side of the picture tube to the left. On
average, no current flows through C2421 and thus the
voltage across this capacitor remains constant.
5430
I Defl
141V
t3 t4
Line defl.
2425
6423
7421
2433
2421
2420
41V
2426
6422
5422
Figure 9-25 Line deflection part 2
•
Period t3-t4: As for the period t2-t3; but now the current
flows in the opposite direction, since the voltage across
C2425 and C2426 is higher than the voltage across C2433
and C2421.
•
Period t4-t5: The coils want to maintain the negative
current and will charge the capacitors negative. Because of
this, D6422 and D6423 will conduct. The voltage is 100 V
across the deflection coil and 41 V across L5422. As both
diodes conduct, we may consider the voltage constant. A
linear current flows with the same changing characteristics
as in period t1-t2. The spot now moves from the extreme
left of the picture tube to the centre. Before the current
becomes zero, and the spot is located in the centre of the
frame, TS7421 reverts into conductivity. First a short
negative current will flow. The cycle starts again.
9.12.3 Corrections
Several corrections are necessary to obtain a correct picture.
Linearity Correction
A constant voltage across the horizontal deflection coil should
result in a linear increasing saw-tooth current. This is not the
case however, as the resistance of the coil is not negligible. In
order to compensate for this, a re-magnetised coil L5421 in
series with the deflection coil is used. This coil ensures that
during time interval t1-t3 the circuit resistance will be higher
than during t4-t5.
L5421 is called the linearity coil. To avoid self-oscillation,
R3431 and C2431 are placed parallel to L5421.
S-correction
Since the sides of the picture are further away from the point of
deflection than the centre, a linear saw-tooth current would
result in a non-linear image (the centre would be scanned
slower than the sides).
To solve this, the deflection current for the right- and left side is
reduced.
C2433 is charged quadratic during time interval t1-t2. Left and
right the voltage across the deflection coil decreases, causing
Circuit Descriptions and Abbreviation List
5430
I Defl
141V
t4
Line defl.
2425
6423
+
7421
2433
2421
-
2420
41V
6422
2426
5422
CL 96532156_025.eps
the deflection to slow down. In the centre, the voltage increases
and the deflection will be faster.
An S-shaped current is superimposed on the saw-tooth
current. This correction is called "finger-length correction" or
"S-Correction".
C2433 is relatively small, as a result of which the saw-tooth
current will generate a parabolic voltage with negative voltage
peaks. The current also results in a parabolic voltage across
C2421, resulting in the finger-length correction, proportionally
increasing with the picture width.
The EW-DRIVE signal will ensure the largest picture width in
the centre of the frame. Here the largest correction is applied.
The larger the picture width, the higher the deflection current
through C2433.
E/W-correction
A line, written at the upper- or lower side of the screen, will be
larger at the screen centre when a fixed deflection current is
used. Therefore, the amplitude of the deflection current must
be increased when the spot approaches the screen centre.
This is called East/West correction.
The EW drive signal originates in the HOP and is supplied to
TS7480 via OpAmp 7450-B and optocoupler TS7482. The
shape of this signal determines the various geometric
t5
correction parameters:
100V
•
H amplitude
141V
•
EW-parabola
41V
•
EW-corner
•
EW-trapezium
231299
•
Horizontal parallelogram
•
Horizontal bow
TS7480 will charge capacitor C2421 more or less, increasing
the deflection current when reaching the centre of the screen.
The moment TS7480 is driven into saturation, C2421 will
discharge during the flyback. As a consequence of which
C2421 must be charged again during the scan via the
conduction diode D6422 (as long as C2421 is not charged to
the voltage across L5422, D6422 will conduct).
The current in the deflection coil is therefore larger than the
current flowing in L5422 (1-2). The voltage across the
deflection coil increases, so the picture width increases. When
TS7480 blocks, C2421 will not discharge anymore, and the
voltage across C2421 will remain constant.
The result is that the voltage across the deflection coil is
minimal. The voltage across coil L5422, however, is maximal.
This coil (L5422) consists of a transformer with the following
properties:
As the current through the coil 1-2 increases (smaller picture
width), the current through coil 3-4 decreases. Because of the
transformer characteristic a higher voltage will be subjected to
coil 3-4, which will counteract the current. The current will
diminish even further.
When the current through coil 1-2 diminishes (larger picture
width), the current through coil 3-4 increases.
Beam-current Correction
The 'EHT-info' signal at point 10 of the LOT depends on the
value of the beam-current and the voltage from divider R3450,
R3451, and C2450. This signal is fed to the HOP to trim the
contrast, and to compensate for the changes in picture-width
as a function of the EHT-info, when EHT is decreased.
The 'EHT-info' is also used to correct the EW-current.
The 'DYN-FASE-CORR' signal, derived from the 'EHT-info'
signal, is fed to the HOP via C2455 and drives a dynamic phase
correction necessary because of beam-current variations. This
is done by regulating T
9.12.4 Secondary Line Voltages
During the blocking time of TS7421, the magnetic energy of coil
1-5 of the LOT is transferred to electrical energy in the
EM5A P/M
9.
of the line transistor TS7421.
ON
EN 133
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