PV152
2-14
PRO1200 CIRCUIT DESCRIPTION
CIRCUIT DESCRIPTION
the end of the horizontal scan in order to obtain suffi-
cient energy at the start of the horizontal scanning. The
trigger pulse is generated in two steps by the two
monoflops of IC401. Integration ( = averaging) of the
pulse train at the output pin 13 results in an automatic
tracking of the trigger moment with the line frequency.
C302 then charges, and its rate of charge is determined
by the condition of the current generator Q300. Q300 is
supplied with the
+ FOC
us voltage from the SMPS, which
is proportional to the line frequency. A vertical parabola
is added to this charging current via C422.
Because of this, a tracking of the amplitude sawtooth
signal with the line and vertical frequencies is devel-
oped.
The sawtooth signal is now applied to:
-
a multiplier IC301 in order to generate a symmetrical
parabolic waveform, regardless of the line frequency.
-
a level detector in IC307 pins 3, 2 and 1 to produce a
left-right squarewave which is buffered by Q307 and feeds
the switchers-clampers Q309 and Q310 with a correct DC
level (note that Q307 is supplied with + / - 12 volts).
-
the inverting input of another level detector of IC307,
pin 6, to produce a left-right squarewave (DRIVER) op-
posite in phase to the one on pin 1 of IC307. This
squarewave is used on the main board to boost the sup-
ply voltage of the line power amplifiers during the sec-
ond half of the horizontal scan.
The parabolic signal from the multiplier, IC301 is buff-
ered with Q302, clamped and buffered. The signal then
goes to the non-inverting inputs of two voltage-follow-
ers in IC309 (MC34084).
Clamper Q310 shorts to ground the parabolic waveform,
during the first half of the horizontal scan, and Q309
shorts the signal during the second half of scan.
The buffered signals are now adjusted in amplitude with
IC311, IC312 and IC313 for the three colors. The out-
puts are summed and sent to the power amplifiers at a
suitable level.
b) At vertical frequency
(Page 6-18 Sect. B-6)
The vertical sawtooth
“VDL”
is DC coupled to a buffer
IC308 pin 3 and then applied to:
- the multiplier IC302 to generate a vertical parabola.
The parabola is inverted with Q304, clamped, buffered,
and feeds two buffers in IC309.
- a level detector IC308 input, pin 5, to produce a top-
bottom squarewave. The output is buffered and feeds
the clampers Q311 / Q312 with a correct DC level for
grounding the input at either the top or bottom half of
the raster.
The two remaining potentiometers of IC311, IC312,
IC313 are used to adjust the top / bottom waveforms
which are again summed and leave the subunit to be
amplified by the power amplifiers on the main board.
c) Static or average focus (center focus)
Three voltages
R STATIC, G STATIC and B STATIC
, adjust-
able b / - 1.5 volts with potentiometers in IC303
are added to the feedback of the vertical focus power
amplifiers.
d) Power amplifiers:
1. CORNER - H
(Page 6-18 Sect. G&F-9)
The left / right adjusted waveforms, summed on the sub-
unit IC309 output, are amplified to generate the re-
quired magnetic field for focusing of the beam during
the horizontal scan. Because of the high scanning range,
a good slew rate of these amplifiers is necessary. This is
especially critical during the second part of the hori-
zontal scan. This can be realized by boosting the supply
voltage during this time.
Boosting the +FOC voltage is done in the circuit around
Q190 - 193. The squarewave drives the push-pull stage
Q190 / Q191, which in turn drives the MOSFETs Q192 -
Q193 . The +FOC voltage is boosted during the second
part of the horizontal scan and is now referred to as
+V[DYN].
Three identical amplifier stages with feedback to the
inverting input of the OPAMPs in IC100 deliver current
to the horizontal focus coils.
2. CORNER - V / STATIC.
Since the vertical scanning frequencies are much lower
than the horizontal frequencies, a TDA2030 may be used.
For stability, a similar feedback voltage is applied on
the inverting input, together with a DC-voltage (=static,
for the center).
B. Horizontal SHIFT
(Page 6-15 Sect. C-5)
The + / - SHIFT voltages are not returned to chassis
ground, but to the
HDL
(Horizontal Deflection Low, which
is basically HTHD). Therefore, the adjusted shift volt-
ages may not be referenced to chassis ground, but to
the same HDL.
The digital potentiometer IC (IC52) has to be supplied
with the + / - SHIFT voltages from the SMPS.
The I2C-bus lines
SDA
and
SCL
must drive the above-
