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(Serial Clock) and SDA (Serial Data) lines which are con-
nected to the microprocessor of the controller board.
The address info, arriving via the data SDA line, is iden-
tified by a hardware connection of the address pins of
the chip (the address pins are differently connected for
each chip ).
Obviously, as there are 4 potentiometers, the address of
the chip is followed by a ' s lave- address' to drive the
requested potentiometer in the chip itself.
d) Vertical Linearity control (Page 6-9 Sect. C-2)
The V PAR (Vertical Parabola) signal at the emitter of Q2
is divided by R23 / R100 and applied to the potentiom-
eter "1" of IC2 (pin 19). The adjusted parabola at out-
put VO1, pin 25, is now sent to the non-inverting input
of IC8 whereas the full amplitude of the parabola is ap-
plied to the inverting input of the OPAMP
(voltage difference amplifier). The output is then added
to the V ST (Vertical Sawtooth) at pin 17 of the same
IC2.
e) Generation of ABL pulses.
Two pulses are generated with the two monoflops in IC15.
The first monoflop is triggered with V_ST and the sec-
ond one with the inverted output pulse of the first one.
*ABL DEFL PULSE: this pulse causes an overshoot in the
vertical deflection at the end of the vertical retrace time
in order to make invisible the spot, as, during this time
the blanking is disabled.
*ABL PULSE: this pulse determines the exact time of
implementation of the black current and the measure-
ment of this implemented current.
f) Vertical output stages - Vertical shift - Vertical
amplitude.
Vertical amplitude - ABL Deflection Overshoot (Page
6-12 Sect. F-3&4)
The vertical sawtooth V_STat the buffer output pin 14 is
leaving the main board and reaches the subunit to be
applied to IC2 (VRN0 and VRP0). The output is VO0 (pin
24) and is coming back to the board at J4 (4) of the
edge connector.
It is now buffered twice with Q27 and Q28.
The switcher Q29 at the base of Q28 is driven with the
ABL DEFL PULSE in order to cause an overshoot in the
vertical deflection during the time the ABL circuit is
active.
It is now capacitively coupled to the inverting inputs
PV152
CIRCUIT DESCRIPTION
of the power amplifiers IC11 / IC12 / IC13 together with
a DC-voltage (Vertical Shift voltage).
The amplitudes for the red and blue can be adjusted by
P626 and P627 to allow a matching with the green and
to minimize the convergence corrections.
Vertical shifts (Page 6-12 Sect. D-4)
These DC voltages are adjusted in IC3 of the subunit
(outputs 25, 26, 27).
The big tolerances on the deflection units and the
stigmators require a coarse alignment of the shift for red
and blue in order to improve the resolution of the digi-
tal potentiometers.
This pre-alignment or coarse alignment is done by the
multiturn potentiometers P620 and P621. The voltages
applied to the extremities of these potentiometers are
inversed when moving the vertical scan inversion switch
(switching from ceiling to table or vice versa).
An " VS I " info is therefore sent to the switching tran-
sistors Q611 / Q612.
This "VS I " is at ground level or not at ground (= 'open').
It is a info coming from the contact of the vertical scan
inversion switch on the frame.
One of the two transistors is in conduction, depending
on the voltage at Q611's base.
When the green raster is moving on the screen, the red
and blue rasters move also allowing a quick adjustment
of the three colors.
Vertical output stages (Page 6-10)
The amplified sawtooth output currents flow in the re-
spective scan coils and find their way back to ground
through the feedback resistors R44 / R97 / R79.
The amplitude of the waveforms across these resistors is
proportional with the vertical amplitude and can obvi-
ously be utilized as feedback to stabilize the vertical
amplitude.
The TDA8172 has an internal boost up circuit which al-
lows a short vertical retrace time by boosting the supply
voltage during the retrace time.
At the end of the scan time, the voltage across the ca-
pacitors C35, C55 and C52 is switched in series with the
supply voltage of +8 volts by means of a transistor in
the chip .
2-9
PRO1200 CIRCUIT DESCRIPTION
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