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20
The picture width, and E-W correction adjustments (pa-
rabola, corner and trapezium) are carried out by modulat-
ing the current across coil Lk1.
The circuit Ck38, Dk9, Rk49 and Rk52 in parallel with S-
correction capacitor Ck27 eliminates the so-called "mouse
tooth" phenomena.
Dynamic focus, FO600
A dynamic focus adjustment is used in addition to the nor-
mal focus adjustment. The dynamic focus improves the
focus on both sides of the screen. In order to have a higher
focus voltage at the beginning and end of the scan period,
an auxiliary voltage is needed. This voltage is taken from a
transformer, which is connected in series with the horizon-
tal deflection coil. The parabolic voltage across the trans-
former is fed via a capacitor to the dynamic focus
potentiometer and onwards to a discrete focus grid. The
dynamic focus is used only in larger picture tubes.
Horizontal scan shift and dynamic focus, FO7xx
Receivers with a VGA connection (Feature box DB700) are
equipped with a special FO7xx module which includes a
horizontal scan shift adjustment, and also, when needed,
dynamic focus.
The horizontal shift control voltage (0...+5 V) is taken from
microcontroller pin 5 to the module connector Xfo3-1. The
connector Xfo3-2 is connected to +12 Vp.
When the control voltage is low, transistor tfo5 conducts.
Due to resistors rfo4, rfo5 and rfo6 the base voltage on
transistors tfo3 and tfo4 is low, causing tfo3 and Tfo1 to
conduct. Diode Dfo2 conducts and capacitor Cfo7 is charged
to the positive voltage, which is fed onward to the deflec-
tion path via resistor Rfo2 and transformer pins 2 and 4.
When the control voltage is high, transistor tfo5 is switched
off and resistors rfo4 and rfo5 are not in parallel connec-
tion with rfo6. This means that the voltage level on the
bases of tfo3 and tfo4 is high, causing tfo4 and Tfo2 to
conduct. Diode Dfo1 conducts and capacitor Cfo6 is charged
to the negative voltage, which is fed to the deflection path.
By varying the control voltage between 0 and 5V, the de-
flection path can be made more negative or more positive,
and thus the horizontal scanning can be shifted sideways.
Capacitors Cfo2 and Cfo3 operate as S-correction capaci-
tors. This means that in VGA sets, the original S-correc-
tion capacitors (Ck27 and Ck33) on the main board are short
circuited.
+30 V
U1
+12 Vp
+17 V
Hor
drive
ZDk1
+53 V
+16 V
Rk11-14
Tsw1
Mk2
Tk1
Tk2
E-W
drive
Capacitor Cfo4 and coils Lfo1 and Lfo2 apply an additional
correction to the linearity.
Diode split transformer Mk1
The primary winding (pin 6) of the diode split transformer
(DST) is connected to the +130 V supply voltage via FET
switch Tsw1. In order to protect the switching transistor in
the power supply, power consumption will be reduced
during the switch off phase by the FET. During normal op-
eration, the FET conducts due to a high level on the gate.
When the TV set is switched off, the +12 Vp drops and tran-
sistor Tsw2 conducts. Capacitor Csw1 discharges through
transistor Tsw3, which conducts and grounds the gate caus-
ing the FET to switch off.
The DST produces the flyback pulses from the primary
winding (pins 6-3) to the secondary windings and gener-
ates the following voltages:
- High voltage (30kV) for the picture tube anode
- Focus and screen grid (Ug2) for picture tube
- Filament voltages for the picture tube cathode from pins
10-11
- +200 V for the video output amplifiers from pins 12-4.
This voltage is rectified by diode Dk1
- +50 V from pins 1-5 or +46 V from pins 2-5 for the vertical
IC. This voltage is rectified by diode Dk2
- +16 V for the vertical IC from pins 7-5. This voltage is rec-
tified by diode Dk3
- EHT information from pin 8 (and Ck21)
Dk2
Rk9
Mk1
Dk3
Rk19
Tk3
Rk2
Dk1
Ck24
Dk7
Dk8
Ck26
Ck28
Tk4
Lk1
Mk3
EHT 30 kV
Focus
Ug2
EHT compensation
Filament 6.3 V
+200 V
Defl
Ck27/33
coil
Lk2
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