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EN 122
9.
9.15.3 Auto Scavem (Diagram SC)
R
Differen-
G
Matrix
Coring
tiator
B
2
I
C
TDA8444
Reserved for
future use
Scavem
action
Clipper
(fixed)
Differentiator
slope
Coring
Figure 9-25 Auto Scavem
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
MATRIX
+12S
SC4
2008
7V9
7006
BFS20
Y_SCAVEM
2V6
(FROM SSB)
1V 9
Figure 9-26 Auto Scavem: Stage 1 and 2
The 2fH RGB signals are added on the SSB (see diagram B4),
and presented to the emitter of transistor 7006.
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.
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.
EM5E
Circuit Descriptions and Abbreviation List
Clipper
Gain
Parabola
Output
modulation
stage
Parabola
Deflection
pulses
Transition
CL 16532149_089.eps
DIFFERENTIATOR
SC5
7V7
9V4
8V 7
BF824
7008
22n
7010
0V
BFS20
3 6000
1
BBY40
6002 1
3
BBY40
DAC7
CL 26532041_082.eps
Coring/Clipping and Gain
CORING / CLIPPING
2012
To
22n
SVM coil
SC6
2014
22n
DAC7 DAC5
Figure 9-27 Auto Scavem: Stage 3 and 4
The coring circuit (items 7014 and 7016) prevent Auto Scavem
on the lowest signal levels (= noise), while the clipper circuit
(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
131201
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
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
2
C. The
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(optional)
+12S
11V9
7200
9V6
2
BC847B
7206
9V0
BFS20
SC13
1
11V8
7012
BFS20
6V9
Optional (depending on the set execution), 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
230402
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
DAC3
PARABOLA GENERATION
11V9
3204
5V
7212
BC847B
47K
7204
BC857B
SC12
11V5
7210
BC857B
2204
3220
BFS20
7202
15K
2206
1u
0V 7
1u
0V
Figure 9-28 Auto Scavem: Stage 5
11V8
7026
DAC6
BFS20
6V9
SC8
6V2
7024
BFS20
0V
0V3
CL 16532149_091.eps
201201
SC11
3222
7208
HEAT
BC847B
6K8
CL 16532149_092.eps
201201
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