Philips 26FW5220, Service Manual

Page: 98 / 150

The audio decoding is done entirely via the Hercules. The IF output from the Tuner is
fed directly to either the Video-IF or the Sound-IF input, depending on the type of
concept chosen.
There are mainly two types of decoder in the Hercules, an analogue decoder that
decodes only Mono, regardless of any standards, and a digital decoder (or DEMDEC)
that can decode both Mono as well as Stereo, again regardless of any standards.
In this chassis, the analogue decoder is used in two cases:
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It is used for AM Sound demodulation in the Europe SECAM LL' transmission.
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It is used for all FM demodulation in AV-Stereo sets.
Diversity
The diversity for the Audio decoding can be broken up into two main concepts:
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The Quasi Split Sound concept used in Europe and some AP sets.
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The Inter Carrier concept, used in NAFTA and LATAM.
The UOC-III family makes no difference anymore between QSS- and Intercarrier IF,
nearly all types are software-switchable between the two SAW-filter constructions.
Simple data settings are required for the set to determine whether it is using the Inter
Carrier or the QSS concept. These settings are done via the “QSS” and “FMI” bit found
in SAM mode.
Due to the diversity involved, the data for the 2 bits are being placed in the NVM
location and it is required to write once during startup.
On top of that, it can be further broken down into various systems depending on the
region. The systems or region chosen, will in turn affect the type of sound standard that
is/are allowed to be decoded.
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For the case of Europe, the standard consists of BG/DK/I/LL' for a Multi-System set.
There are also versions of Eastern Europe and Western Europe set and the
standard for decoding will be BG/DK and I/DK respectively. FM Radio is a feature
diversity for the Europe sets. The same version can have either FM Radio or not,
independent of the system (e.g. sets with BG/DK/I/LL' can have or not have FM
radio).
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For the case of NAFTA and LATAM, there is only one transmission standard, which
is the M standard. The diversity then will be based on whether it has a dBx noise
reduction or a Non-dBx (no dBx noise reduction).
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For the case of AP, the standard consists of BG/DK/I/M for a Multi-System set. The
diversity here will then depends on the region. AP China can have a Multi-System
and I/DK version. For India, it might only be BG standard.