Dynamic Focus Circuit - Tatung OMNISCAN SERIES Service Manual

N1 24 Vpp
3.48 DYNAMIC FOCUS CIRCUIT
FOR DYNAMIC FOCUS MODEL ONLY
(SUCH AS PB8520SV jMD6AjMD7 Aj
CM-17MBDj20MBD)
In order to get the optimum focus, the focus voltage
must be changed for each beam landing position.
This is called dynamic focus. The· optimum focus
voltage waveform is parabolic both horizontally as
well as vertically. Dynamic focus is normally achieved
by shaping, processing and amplifying the waveform
of both deflection currents.
FOCUS
Focus 1 should be adjusted so that the vertical lines
become narrowest in all over the screen.
Focus 2 should be adjusted so that the horizontal
lines become narrowest in all over the screen.
Network 0705-0706 is cascade amplifier, C709-R733
is used to apply an AC voltage to the focus electrode.
TEST TEST TEST POINT NAME
CONDITION POINT
Fh=31KHz
T1
T1 V SAWTOOTH SIGNAL INPUT
T2 V PARABOLA SIGNAL INPUT
T3 BASE SIGNAL
T4 V PARABOLA SIGNAL OUTPUT
2.5 Vpp
,
----'-~--..;--)
T2 8.2 Vpp
T3 5.2 Vpp
T4 200 Vpp
3.49 VERTICAL PARABOLA SIGNAL GENERATOR
(Refer to circuit diagram Fig-49)
The ramp voltage produced across R312 is integrated
by 0707a via pin 2 of P703 and the resulting parabola
is amplified by 0707b, the resulting parabola is used
to provide vertical focusing. A single transistor
amplifier 0708 performs the basic function. The level
of vertical . parabola signal is controlled by R722-
R724-R727-R728 of the amplifiers.
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