Philips 29PT5445/85 Service Manual page 45

Circuit Descriptions, List of Abbreviations, and IC Data Sheets
The selected external audio source is then fed to the AN5829
AUX1 input (pins 2 and 3). The AV2 is fed directly to AN5829
via AUX2 (pins 23 and 24). Then via I2C, the AN5829 IC source
selection can be done.
9.2.2 Switching Function for Mono I/O
For the Mono configuration, only one input pin is available for
the UOC.
Video Source Selection
The video switching is similar to the section above.
Audio Source Selection
The audio input (L1_IN) is connected to pin 35 of the UOC.
9.3 Audio
This chassis is targeted for the NAFTA market with Mono,
Stereo, or SAP sound system.
For the "basic" Mono and Stereo sets, sound processing
includes Volume control and AVL.
For stereo sets, IC AN5829S is the BTSC audio signal decoder
and AN5891K is the audio processing IC.
9.3.1 Processing
This chassis uses the Intercarrier demodulation concept (one
SAW filter for both video and audio). The base band (full
bandwidth) BTSC audio signal from the UOC is fed to pin 14 of
the stereo decoder. The Pilot detection and SAP detection
registers indicate the type of transmitted audio signal such as
Mono, Stereo, and/or SAP. Based on this indication, the
software controls will help to output the appropriate audio
signal at pins 21 and 22. The controls are done by the I2C bus
connected to pins 18 and 19.
Internal or External audio (pins 2, 3, 23, and 24) can also be
selected by the source selection register. For the selected
audio source, the AGC function can be applied. The output is a
fixed level output. The volume control function is available via
the power amplifier (AN7522/23).
The selected audio output from IC7841 (AN5829) is fed to pins
3 and 22 of IC7821 (AN5891) for audio processing functions,
such as Treble, Bass, Volume, Balance, and Surround sound
functions. L_out and R_out are then available on pins 12 and
15.
IC7821 is also I2C controllable (pins 13 and 14). An AVL
function is also available in this IC, and can be used for sets
using this IC. In this case, the AVL function of the AN5829 is
disabled. Subwoofer output (optional) is available on pin 20.
9.3.2 Amplifier
The output is fed to the audio amplifier (IC7901 for stereo sets
or IC7902 for mono sets). This is a BTL amplifier (Bridge Tied
Load), which is actually a class AB amplifier with four
transistors for each channel. The advantage of BTL over the
standard Class AB amplifier is that it requires a lower supply
voltage to deliver a higher output.
The volume level is controlled at this IC (pin 9) by the
"VOLUME" control line coming from the microprocessor. After
amplification, the audio signal is send to the speaker /
headphone output connector.
9.3.3 AVL (Automatic Volume Limiting)
The "Mono AVL" function operates via the UOC. During
channel change and source selection, the AVL bit is to be
switched "off" and then can resume to the previous state ("on/
off") as shown in the timing diagram below.
L03.1U AA
The "Stereo AVL" function operates via the AGC control of IC
AN5829S. During channel change and source selection, the
AGC function is to be switched "off" and then can resume to the
previous state ("on/off") as shown in timing diagram below.
user press
Ch+ / Ch- or
change
source
Mu te/Volume
Mono: AVL_ On/Off
Stereo: AGC_On/Off
channel / source
change active
Figure 9-3 AVL timing diagram
9.3.4 Mute
The TV set must mute:
• Whenever a "User Mute" is activated.
• Whenever there is a channel change, RF to RF, RF to AV,
AV to RF, and AV to AV (if any). In channel change, MUTE
must be activated first before any other activity and un-
MUTE must be done after every other activity has been
completed.
• Whenever there is a loss in the signal.
• During cold or warm start, MUTE must be activated until all
initialization processes are finished.
• When the set is going to STANDBY, MUTE must be
activated first before any other activities.
Note:
1. MUTE mentioned above applies for the audio amplifier
mute (= PWM volume control mute).
2. The first condition does not apply for the UOC, IC
AN5891K, or IC AN5829S.
3. Above conditions refers to both mono and stereo sets.
9.4 Video
For a detailed circuit description of this part, we refer to the
L01.2L AA manual (see the beginning of this chapter for the
ordering codes). Please note that there can be minor
differences in the text (e.g. other item numbers), but the
described circuit principle is comparable.
This chassis uses the TDA937x family Ultimate One Chip TV
processor (UOC), which is mounted in an SDIP 64 envelope.
The various versions of the UOC series combine the function
of a video processor together with a microcontroller and US
Closed Caption/TXT decoder.
9.5 Synchronization
Inside IC7200 (part D) the vertical and horizontal sync pulses
are separated. These "H" and "V" signals are synchronized
with the incoming CVBS signal. They are then fed to the H- and
V-drive circuits and to the OSD/TXT circuit for synchronization
of the On Screen Display and Teletext (CC) information.
9.6 Deflection
For a detailed circuit description of this part, we refer to the
L01.2L AA manual (see the beginning of this chapter for the
ordering codes). Please note that there can be minor
differences in the text (e.g. other item numbers), but the
described circuit principle is comparable.
9. EN 45
200 msecs Volume Ctrl Voltage
50 msecs
150 msecs
50 msecs
CL 36532044_038.eps
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