Service manualCHASSIS 2112-Series EC7-A
The IF of AM sound is basically formed by IC1400, integrated circuit TDA9830T, and by the surface acoustic wave
SF1400. Its input is the output of tuner intermediate frequency. Its output is the AM demodulated monaural audio
signal.
The operation is the following: the surface acoustic wave SF1400, it has an only one resonance at the carrier
frequency of the AM modulated sound signal; therefore, it only allows the pass of this signal, which is regenerated
and self-multiplied, giving as result the demodulated signal. This circuit does not require adjustments.
4.8.3 L? system.
The L? transmission system, used in France, differs mainly from L system in the signal spectrum, which is in
frequency inverted and it is only used in channels of band I. This is why in the tuning menu of TV sets with L?
system, when the system is France, there is an additional band, VL?. It covers the same channels as band VL but in
band VL reception is made in system L?.
In order to carry out the signal reception with inverted spectrum, what must be done in this chassis is to change the
intermediate frequency of the picture carrier of 38,9 MHz from the rest of systems to 33,9 MHz. Therefore, the
surface acoustic wave of picture, SF200, is intended to work both frequencies of picture carrier in TV sets that have
this system.
As far as the sound, the intermediate frequency of its carrier changes from 32,4 MHz with system L to 40,4 MHz
with system L'. Therefore, in TV sets with system L', the surface acoustic wave, SF1400, can be switched between
both frequencies by the microprocessor, by means of the circuit associated to D1200 and D1201. The control signal
is - LP/L
4.8.4 Audio switching.
The audio switchings are carried out by means of: IC400, IC1401, IC1400 and by -RADIO (pin 10 de IC100), -AM;
SCART (pin 11 de IC100) and -AM; FM (pin 13 de IC100) signals.
IC400 allows selecting between a FM sound coming from the tuner signal and an external audio signal. The audio
supplies are three, SCART audio (S900) in parallel with the frontal RCA (S902), AM audio for TV sets with SECAM
L standard and audio of FM radio for models with radio. The audio output through the SCART can be sound from
the tuner, radio sound or AM sound. The table and the diagram of switchings, that allow all these possible
combinations, are the following ones:
-RADIO-AM;-AM; FMExternal AudioSpeakers outputSCART output
SCARTselected
111Frontal SCART/RCATuner or AV (depends onTuner
the user)
100AMAMAM
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ACEC
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