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will again decrease, followed by another start-up cycle
(Burst Mode ). The amount of power taken up from the
mains in burst mode is low.
Standby modes:
In the 'AV-Standby' operating mode of the set, the 'ION'
control line is primarily used to switch off all output
voltages for DVDR mechanism and Digital Board
(supplies 3V3, 5V, 12V, 5N and 4V6 at Connectors 1932
and 1933) of the power supply. This reduces the amount
of power taken from the mains. In Low Power Standby
mode additionally the 'STBY' control line is used to switch
off output voltages 5SW and 8SW. This reduces power
consumption to less than 3W, if additionally the display is
switched off. The power supply will continue operating in
Standby mode with a switching frequency of approx. 25
kHz.
3.3 Frontend
This unit is designed to support two basic versions, which
are distinguished by a different assembly variant only (one
for multistandard and the second for Pal-I only) and
comprises the following parts:
• Tuner UV1316K [1705]
• IFamplifier& video demodulator IC TDA 9818/9817
[7710]
• Sound processor MSP3415G [7600]
Tuner and IF selection
The Tuner [1705] converts the RF-signal coming from the
antenna input to an IF-signal. The tuner is fully controlled
via I 2 C-bus of the CC-P. [1705] is also equipped with a
"passive-loop-through" between antenna-in and -out to
save power in stand-by of the set, when the complete part
is not supplied.
The IF frequency of the video carrier is 38.9 MHz for all
systems except SECAM L' (34,0 MHz).
A quasi-split audio system is used. Separate surface-
wave filters (SAW) are required. [1701], [1703] for video,
[1702] for audio. [1701] is switched into the signal path for
DK/I-SECAM L/L' reception, if the signal "SFS_TS" is
"high". In this case the switches [7704], [7705] are open
and the diode [6703] is conducting. [1703] is switched into
the signal path for BG reception ("SFS_TS" is "low"). Then
the switch [7712] is open and the diode [6704] is
conducting. For DK/I-SECAM L/L' reception, an additional
circuit for suppressing the audio carrier of the adjacent
channel is used. This circuitry is adjusted by coil [5710] for
maximum suppression at 40.4MHz.
IF demodulator
The signal from the tuner and IF-selection circuit is
processed by the demodulator IC TDA 9818/9817 [7710].
The signal "PSS" to pin 3 switches between demodulation
of positive (SECAM only) or negative modulated video
carriers. A QSS-audio-IF signal SIF1 is generated for
demodulation in the sound processor [7600]. The audio-IF
carrier is selected in the audio SAW filter [1702]. This filter
is switched for SECAM L'. If the signal "SB1" is "high", the
switch [7714] is closed and the diode [6705] is not
conducting. For all other standards the diode [6705] is
conducting and the switch [7714] is open. The output
signal of this SAW filter is firstly processed in the TDA
9818. Audio carriers are converted from the tuner IF level
to the audio IF position and further processed in the audio
demodulator [7600]. The AFC coil [5711] on the TDA
9818/9817 is adjusted so that when a frequency of 38.90
MHz is supplied to the IF output of the tuner, the AFC
voltage on pin 17 of [7710] is 2.5V. The setting of the
picture carrier frequency for SECAM L in the TDA 9818 is
achieved by connecting pin 7 of the IC via a resistor [3710]
to ground. The switch [7701] and the signal "SB1" do this.
The HF-AGC is set using the potentiometer [3724] so that,
with a sufficiently large antenna input signal (74 dBV), the
voltage at the IF output of the tuner [1705] pin 11 is 500
mVpp. This setting must be carried out when the audio
carrier is switched off. The demodulated video signal
appears on pin 16 of [7710]. The AGC voltage at pin 4 is
used to determine the antenna signal strength after a
buffer [7717] with the signal "AGC" and an analog input
port of the CC-P. The trap [1704] reduces the sound
carrier remainders in the video for BG standards. The trap
[1706] works in the same way for the Pal-I standard only.
For all other standards the switch [7713] is closed via
[7706] and "SFS_TS"-line set "high" to bypass this trap. In
these cases the selectivity of the SAW filter [1701] is
sufficient. The coil [5713] for non-BG standards realizes a
frequency response correction. This correction is not
desired for SECAM L' and therefore short-circuited by
[7716] (signal SB1 is "high" and [7702] has on-status). The
demodulated video signal "VFV" is available after the
buffer and limiting stage for noise peaks [7711]. The FM-
PLL demodulator function of TDA 9818 is not necessary
and therefore deactivated by the resistor [3739].
Audio demodulator
The sound demodulation is done by the MSP3415 [7600],
which is also fully controlled via I 2 C-bus by the CC-P
(determination of bandwidth, amplitude, standard, ...).The
audio signals are available at pin 30 and pin 31 of [7600]
and fed as "AFER"- & "AFEL"-line to the audio-I/O for
further processing.
DRX-2
101
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