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Colour television
1.
New audio stereo modules in L6.1 AA chassis
In the L6.1 AA chassis two new modules are introduced:
a NICAM-stereo module and a 2CS-stereo module
(2CS means two carrier sound).
The NICAM stereo module will be available in the following
executions: NICAM L, I, BG. This module will also be used for
2CS BG/DK sound demodulation.
Depending on the execution whether the module has to act
as a NICAM or as a 2CS module, IC7221 is a MSP3410
(Nicam) or a MSP3400(2CS).
The 2CS stereo module is only for the BG-only execution.
Circuit descriptions
2.
NICAM module
The input-signal for the NICAM-module is the IF-signal
directly from the tuner. This signal is fed to bandpass-filter
1201 and to bandpass-filter 1200. Bandpass-filter 1201 is
used to select the video-signal which is necessary to lock the
PLL inside IC7206. This PLL is used to modulate the
FM/NICAM signal on output pin 20 on the right carrier.
Filter 1200 is a switehable filter which can switch between 33.4
and 38.9 MHz. In this way the sound can be demodulated on
both carriers. If system L' is chosen, TS7203 is conducting due
to the fact that signal L/L' is high. In this way TS7202 is out of
conduction and input 1 of filter 1201 is chosen. In all other
systems input 2 of filter 1200 is chosen. L/L' is also used to
select the right centre frequency of the PLL inside IC7206.
AM-sound is completely demodulated in IC7206 and fed to
pin 55 of IC7221. At this 1C the AM sound is used as a
selectable input.
IC7221 is fully IIC controlled by the microcontroller of the set
and in this way the sound can be fully controlled (also the
volume).
The outputs of IC7221 are directly fed to the audio-amplifier
(IC7205). At the input of the audio-amplifier two transistors are
present to prevent that a plop can occur during switching off
of the set. These transistors are TS7209 and 7208. When the
set is switched off the base of these two transistors is
negative due to C2209 and 2210. In this way the two inputs
of the audio 1C are short-circuited.
3.
2CS stereo module
The input for the 2CS-stereo module is the baseband-CVBS
signal coming from pin 7 of connector 0020. The audio-signals
present on the carriers of 5.5 ((L+R))/2) and 5.74 MHz (R) are
separated by filter 1723 which is a bandpass-filter on 5.5 MHz
and filteri 724 which is a bandpass-filter on 5.74 MHz.
On the output-pin 8 of IC7720 the baseband-signal «L+R)/2)
is present and on pin7 the baseband signal (R) is present.
This information is fed to IC7721 to dematrix these signals
into the signals (L) and (R) or into language I and language II
depending on the information present. This depends on the
frequency on which the pilot-tone is modulated. This is detec-
ted by the circuit around L5722.
The dematrixed information is present on the output pins 1 1
a n d 12 of IC7721. This information is fed to a source-select
1C (1C 7724) in which a selection is made between internal
and external sound. This is done by the signal INT-EXT from
the microcontroller of the set. The output of IC7721 is also
fed to the scart-connector.
After the source select 1C (1C7724) the information is fed to the
audio-amplifier (IC7722). The volume of the sound is
controlled by the signals Vol-L and Vol-R which come directly
from the micro-controller of the set. The circuit around TS7731,
TS7732 and TS7730 is an anti-plop circuit. This circuit will pre-
vent plopping sounds during switching off the set. If the set is
on, the base of TS7730 is positive and in this way TS7731 and
TS7732 will not short circuit the inputs of the audio 1C.
However switching off the set will cause a negative voltage on
the base of TS7730; the two transistors TS7731 and TS7732
will then connect to ground the audio amplifier inputs via pin 2
and pin 8.
Option menues of the 2CS version using the TDA9840:
In sets with the 2CS stereo-module with the TDA9840 1C, an
additional selection is possible in the option menu. This
option is called STEREO-LEVEL. This menu offers the
possibility to adjust the stereo level of the TDA9840.
Error-codes
0
No error
Ram error
1
2
IIC bus error
EEPROM error
3
4
TDA9840 or MSP3410 error
4.
Correction of service-code numbers
In the L6.1 AA manual the codenumbers of the micro-
controller (1C 7600) are not published correctly.
The correct code-numbers are:
4822 209 13083 for L6NOTXT-1.0
4822 209 13085 for L6NOTXT-2.0
4822 209 14646 for L6TXTMEU-1.0 (Teletext version 1.0)
Alignments
5.
2CS module
In sets with the 2CS stereo-module (BG-only) the stereo level
can be tuned by software. This has to be done at the following
way:
Chassis
L6.1
AA
97.01
- -
(No Teletext version 1.0)
(No Teletext version 2.0)
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