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EN 150
9.
With normal Scavem (as used in the MG3.1E), the RGB signals
are added together and differentiated before they drive the
Scavem coil. The coring block prevents that Scavem
processing is done on low signal levels.
9.5.3
Auto Scavem (Diagram SC)
Block diagram
R
Differen-
G
Matrix
tiator
B
2
I
C
TDA8444
Scavem
action
Clipper
(fixed)
Differentiator
slope
Coring
Figure 9-10
This new Auto Scavem circuit include some extra blocks:
•
Clipper
•
Parabola modulation
Auto Scavem is fully software controlled, by means of I
speed, at which Auto Scavem is adapted, is controlled by the
Auto TV algorithm. This adaptation takes place together with
the FBX initialisation, and takes about 1 second. The different
circuit stages are controlled via a DAC (item 7500, TDA8444).
The new Auto Scavem circuitry also produces higher Scavem
currents, which results in sharper pictures. For the circuit
description, we splitted the circuit in eight stages.
Matrix and Differentiator
Stage 1 and 2
MATRIX
3006
+12S
+12S
2K2
3012
3V7
3000
5K6
BC857B
R-VC
3V
7000
2000
100R
0V
RES
5p6
SC4
3008
+12S
7V9
2K2
3V7
3014
7006
3002
2K7
BC857B
BFS20
G-VC
7002
3V
2002
2V6
100R
1V 9
0V
RES
15p
3010
+12S
2K2
3016
3V5
3004
15K
BC857B
B-VC
7004
2V9
100R
2004
0V
RE S
2p7
Figure 9-11
The RGB signals are added via transistors 7000, 7002 and
7004, on the emitter of transistor 7006. This is done via
resistors 3012, 3014, and 3016, which have a different 'weight'
factor. This, to regain the luminance signal.
The next circuit is the differentiator. The combined signal
enters this circuit at the base of transistor 7008. The DC-level
of this transistor is controlled by the DAC7 line, which is
dependent of the 'sharpness meter' reading in the Auto TV
algorithm. By means of this control signal, the voltage and
capacity of varicap diode 6000 is altered, which will adapt the
differentiator.
MG3.2E
Circuit Descriptions, Abbreviation List and Data Sheets
Coring
Clipper
Gain
Parabola
Output
modulation
stage
Parabola
Reserved for
future use
Deflection
pulses
Transition
CL 16532149_089.eps
DIFFERENTIATOR
SC5
7V7
9V4
2008
8V 7
BF824
7008
22n
7010
0V
BFS20
3 6000
1
BBY40
6002 1
3
BBY40
DAC7
CL 16532149_090.eps
The slope of the differentiator is controlled by this DC-level.
The differentiation itself is done by varicap diode 6000. Output
signal goes from the collector of transistor 7010 via emitter
follower (= buffer) 7012, to the next stage.
Coring/Clipping and Gain
Stage 3 and 4
CORING / CLIPPING
To
SVM coil
2012
22n
SC6
2014
22n
DAC7 DAC5
The coring circuit (items 7014 and 7016) prevent Auto Scavem
on the lowest signal levels (= noise), while the clipper circuit
131201
(items 7018 and 7020) always give the same amount of
Scavem above a certain level.
The levels at which this must happen, are controlled by the
DAC4 and DAC5 lines, and are dependent of the 'noise meter'
reading in the Auto TV program.
The input signal enters this circuit at emitter follower 7022, and
2
C. The
is strongly attenuated via voltage divider R3062 and R3064.
This, because the gain of transistor 7024 is set with the
adjustable voltage divider of R3066, R3068 and R3070. The
level at which this happen, is controlled by the DAC6 line, and
is dependent of the 'sharpness meter' reading in the Auto TV
program, the picture tube size, and the sharpness setting by
the customer.
Parabola Generation
Stage 5
+12S
11V9
7200
9V6
2
11V8
BC847B
7012
7206
BFS20
9V0
BFS20
6V9
SC13
1
201201
In addition, the Scavem signal is modulated with a parabola.
This is necessary, because the picture tube is less sensitive for
Scavem in the centre as on both sides.
On the CRT-panel, the 'heater' pulses are used to create a
parabola on line frequency. This parabola is made with
transistors 7204 and 7206. The DC-level of these transistors is
controlled via the DAC3 line. In this way, you can control the
parabola via software. The level is dependent of the 'sharpness
meter' reading in the Auto TV program, the picture tube size,
and the sharpness setting by the customer.
GAIN
11V8
11V8
7018
BFS20
11V
BF824
7014
7022
BFS20
SC7
3062
2020
2K2
22n
2018
7016
0V8
RE S
10p
BFS20
0V
BF824
7020
0V
Figure 9-12
DAC3
PARABOLA GENERATION
11V9
3204
5V
7212
BC847B
47K
7204
BC857B
SC12
11V5
7210
BC857B
2204
3220
BFS20
7202
2206
15K
1u
0V7
1u
0V
Figure 9-13
11V8
7026
DAC6
BFS20
6V9
SC8
6V2
7024
0V
BFS20
0V3
CL 16532149_091.eps
201201
SC11
3222
HEAT
7208
BC847B
6K8
CL 16532149_092.eps
201201
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