Circuit Descriptions, Abbreviation List, and IC Data Sheets
9.
ENABLE signal is grounded via R3403. This will switch 'off' the
main supply (see diagram A1).
Frame Output Protection
The frame output stage is guarded by the circuit built around
TS7641. If the frame output stage is working properly, TS7641
and TS7652 will both conduct, and thereby discharge C2642.
TS7443 is blocked, so the SUP-ENABLE signal is 'high.'
If there are frame pulses missing, TS7641 will block and
capacitor C2642 is charged. Transistor TS7443 starts
conducting and the SUP-ENABLE signal is grounded via
R3403. This will switch 'off' the main supply (see diagram A1).
ARC Protection
If there are 'open' connections (for example, bad solder joints)
in the high-energy deflection circuitry, this can lead to
damaging effects (fire). For that reason, the E/W current is
sensed (via 3479//3480). If this current becomes too high, the
'thyristor' circuit (TS7653 and TS7654) is triggered. TS7442 is
switched 'on' and TS7443 is forced into conduction. The 'SUP-
ENABLE' signal is now shorted to ground level, which will force
the Main Power Supply into Standby mode.
9.13
Audio (Diagram B6, B10, and A6)
The EM1.1A chassis contains ITT's Multi-standard Sound
Processing (MSP IC, type MSP34xx) for sound decoding.
This IC takes care of the main FM sound decoding. All MSP
versions contain digital audio processing used for the basic left/
right stereo sound, such as bass, treble, balance, incredible
sound, and spatial. In addition to that, the MSP3451 is also able
to perform 'Virtual Dolby;' a Dolby approved sound mode for
surround sound reproduction with left/right speakers only.
The MSP3451 is capable of supporting four stereo inputs.
Therefore, an extra input selector (HEF4052) is not needed. It
has a separate headphone output, so sound control can be
performed separately from the speakers.
9.13.1
Inputs / Outputs
Inputs: The MSP can cover four stereo inputs and one mono
input.
Outputs: CVBS/decoder out, record select/WYSIWYR (What
You See Is What You Record), and headphone.
9.13.2
Audio Decoding
The incoming signal is fed to the AGC. After this, an ADC
converts the IF-signal to a digital signal.
Two demodulation channels process this digital signal. The first
one is able to handle FM.
This channel contains a mixer to shift the incoming signal in the
frequency domain. This shift is determined by the value of a
DCO (Digital Controlled Oscillator).
After the down-mix, the signal is fed, via a filter, to a
discriminator. From here the FM demodulation can be
performed.
Both channels contain an 'automatic carrier mute' function,
which automatically mutes the output of the analog section
when no carrier is detected.
After demodulation, the FM-signals are subjected to a
deemphasis operation. After that, the matrix of the stereo
system is applied.
Figure 9-15 Audio decoder block diagram
In the figure above, a simplified block diagram of a stereo
sound system in a TV set shows the 'L+R' audio signal
combined with the detected 'L-R' audio signal to develop stereo
'L' and 'R' audio.
The 'pilot' signal is doubled in frequency (to 2fH) and re-
inserted into the detection of the 'L-R'. This completes the
detection.
The pilot signal also tells the control circuit when a pilot
frequency is present. The 'L-R' and 'L+R' audio are supplied to
the stereo matrix. There, by addition and subtraction, the single
'R' and 'L' audio signals are output. The SAP audio is detected
and made available. In addition, the indication of a SAP signal
is given to the control circuit.
9.13.3
Audio Processing
The sound processing is performed completely by the MSP:
•
Volume control is performed by the user via the "SOUND"
menu.
•
Tone control in 'Stereo' sets is performed via the "BASS/
TREBLE" control.
•
Headphone control: the MSP has a separate Headphone
output so separate sound control is possible.
Automatic Volume Leveling (AVL)
One of the features of the MSP-family is Automatic Volume
Leveling (AVL). If used, AVL limits large volume differences in
the broadcast between television programs and commercials,
or within a movie.
To be able to get a Dolby approval (for the Virtual Dolby sets),
the AVL feature must be switchable. Therefore, the AVL
feature is customer switchable via the menu.
9.13.4
Audio Amplifier (Diagram A6)
The audio amplifier part is very straightforward. It uses an
integrated class B power amplifiers (TDA7497). It delivers an
output of 2 x 10WRMS to two full range speakers and/or
subwoofer.
The supply voltage is +35 V, generated by the main supply via
L5506.
Muting is done via the 'SOUND-ENABLE' line connected to pin
9 of the amplifier IC and coming from the Painter. This signal is
inverted by TS7730, as a result of which at a high level of the
'SOUND-ENABLE' signal, current is sinked from pin 9, and the
IC mutes.
9.13.5
Headphone Amplifier (Diagram B10)
The headphone amplifier is a straightforward OpAmp amplifier
(IC7681, NJM4556). It is supplied with +8 V.
CL 16532043_021.eps
080501
BASEBAND AUDIO
L+R
DEMODULATOR
STEREO
DECODER
PILOT
DET
2X
LEFT AUDIO
RIGHT AUDIO
PILOT DET
SAP DETECT
SAP
DECODER
Содержание Chassis EM1.1A AA
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