PV152
2-18
PRO1200 CIRCUIT DESCRIPTION
CIRCUIT DESCRIPTION
to the ASIC where it is divided down to
HFB
and re-
turned to the phase comparator of the PLL.
When an internal pattern is selected, required by the
user or automatically at start up, the ASIC generates
sync signals HSO and VSO.
The R, G and B together with the INSERT are buffered
with IC31 and further proceed to the RGB INPUT + SW
module.
PLL
(Page 6-34 Sect. G-6)
The PLL consists of the digitally edge controlled phase
comparator IC15, the low pass filter around IC14, the
VCO (Q1 - Q12) and the internal divider in the ASIC. The
VCO is a sawtooth generator. C36 is charged up via Q5,
driven in the base with the low pass filter output. Note
that 0 volts on the base means the maximum frequency.
The VCO_0/1/2 lines can turn transistors on and then
additional current is available for the generator.
Via the emitter/follower Q1 and the buffer in IC39, the
pixel clock is applied to the CPP input of the ASIC. The
PLL phase comparator has a double task. Tune the fre-
quency of the VCO to a multiple of the line frequency
and lock the position of the text to the deflection.
The active line period is divided into 256 pixels to po-
sition 32 characters on a line in the low frequency range
and into 512 pixels (64 characters) in the high freq.
range (see Hor defl module) .
The
HFM
line informs the processor and thus the PLL on
the flyback time, this information is needed to deter-
mine the pixel frequency of the PLL.
Coincidence
The coincidence of the line oscillator is important in-
formation for the controller. At start up, the controller
always generates first internal sync, which must lead to
a coincidence situation.
If an external source is selected, the controller waits for
coincidence and the timings of the selected source. These
timings are needed to choose the memory block corre-
sponding with the source. If the coincidence is not ac-
tive, the projector reMain blanked (black screen).
809-10452
Technical description “Convergence OUTPUT”
(Page 6-31)
The purpose of the power amplifiers is to bring the ad-
justed signals to a sufficiently high level that the con-
vergence coils can be fully driven. It is Important that
the drift be kept as low as possible and that the signals
be carried to the coils without using coupling capaci-
tors.
The coils react differently on signals at a high (line)
frequency than on low frequency signals. Much more
power is required for the high scanning than for the low
scanning range. The power / - CONV for these
power amplifiers is a variable line frequency tracked volt-
age delivered by the “G2 + Diagnostic” board.
Six identical amplifiers feed the six convergence coils,
two for each picture tube. We present only the amplifier
served with
“RHin” (Red Horizontal).
Note that “Horizontal” here relates to the moving direc-
tion (of lines of a crosshatch pattern) and not to the
“horizontal” frequency. The “RHin” signal contains wave-
forms at line and vertical frequency.
That is also the reason the amplifier stages are identical.
The signal RHin is passed on to the power amplifier IC1,
pin 6. These power amplifiers are fully integrated hybrid
amplifiers supplied with +CON and -CON.
The output current flows in a 150 Ohm damping resistor
across the convergence coils and a series feedback resis-
tor of 4.7 Ohm. The voltage developed across this resis-
tor is sent back to the inverting input of the amplifier
for stability.
Note that the jumpers J12 and J13 can be removed in
order to isolate the power stages of the convergence
and thus to investigate whether an excessive load on
the supply voltages of the whole convergence board is
caused by one of these amplifiers (or caused by another
power amplifier of this convergence module).
The current of the +CON and -CON is permanently moni-
tored by Q50 and Q51. The current from the + CON devel-
ops a voltage across SR1 that is applied to the base of
Q50. The current taken from the - CON does the same for
Q51. As soon as Q51 is switched on, the (I) Limiter turns
on Q22 on the Convergence Driver PCB and the sawtooth
generator is inhibited.
809-10463
Technical Description
“ DYNAMIC ASTIGMATISM “
(Page 6-20 to 6-23)
The waveforms for the dynamic astigmatism are para-
bolic and resemble the waveforms for the convergence
corrections. The adjusted waveforms in the Bella’s are
delivered by, and come from, the convergence driver
board.
