Circuit - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
Horizontal
deflector
C541
C543
E/W
charging
coil
C590
2.5.1

Circuit

The components of the east/west output
stage, as well as the diode modulator are lo-
cated on the basic board.
W511
Q534
Pin1
Hor.
Q597
R598
C581
C596
R581
R596
R582
Q582
Q589
Q596
C582
R583
Document Q 2500
D539a
Splitting-
transformer
T531
Q534
D539b
UB
E/W correction
L543
L539 L541
C531
C541
D539a
C543
D539b
L536
R587 L588
U12
R588 C588
R589
C589
Q593
Q593
R593
R584
R592
R585
R591
Q586
R586
C590
The video/deflection processor TDA 9332 ap-
plies a d.c. underlying parabola type voltage
to pin 3. This Information contains all correc-
tions for picture width and east/west. The fol-
lowing amplifier stage, consisting of transis-
tors Q 582 to Q 589, could therefore be im-
plemented simply as a conventionally based
differential amplifier.
Control is via low-pass filter R 581, C 581 and
R 582 on the base of transistor Q 582. The
low-pass filter suppresses any noise compo-
nents from the pulse width generator in
I 2521.
The base of transistor Q 589 is determined by
the voltage divider R 588/R 589 in d.c. and
thereby determines the operational point of
the differential amplifier.
The amplification of the differential amplifier is
determined essentially by the relationship of
the negative feedback resistance R 583 and
the output resistances R 581/582. The parab-
ola type voltage, amplified to 12 V by output
stages Q 585 and Q 586, is fed via the E/W
charge coil to the diode modulator. Dual diode
D 539 superimposes the deflection current on
it and the E/W correction is implemented.
Transistor Q 593 was incorporated to protect
the output stage transistor Q 586 in the event
of the deflection connector being withdrawn.
Normally Q 593 acts as positive feedback to
Q 586. If the deflection connector is withdrawn
the current increases through Q 586 and
L590
therefore also through resistors R 591 /R 592.
This causes Q 593 to conduct and the power
loss in Q 586 to be returned to a normal level.
In the event of a fault the two transistors
Q 596 and Q 597 ensure that the unit
switches to protective operation. Q 596 is
conductively controlled by a reduced base
voltage. Q 597 conducts and controls VPROT
at low level. The CCU protective circuit re-
sponds and switches the unit off.
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