Philips EM5E Service Manual Download Page 122

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Circuit Descriptions and Abbreviation List

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EM5E

9.15.3 Auto Scavem (Diagram SC)

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

C. The

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

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.

Coring/Clipping and Gain

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
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
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)

Figure 9-28 Auto Scavem: Stage 5

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
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.

CL 16532149_089.eps

131201

Differen-

tiator

Coring

Clipper

To
SVM coil

Matrix

Coring

Differentiator
slope

Transition

R
G
B