Philips 7603 series, Руководство по обслуживанию

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The L8/M8 is divided into 2 basic systems, i.e. mono and stereo sound. While the audio processing for the mono sound is
done in the audio block of the UOC, an external audio processing IC is used for stereo sets. The tuning system features 181
channels with on-screen display. The main tuning system uses a tuner, a microcomputer, and a memory IC mounted on the
main panel.
The microcomputer communicates with the memory IC, the customer keyboard, remote receiver, tuner, signal processor IC
and the audio output IC via the I2C bus. The memory IC retains the settings for favorite stations, customer-preferred
settings, and service / factory data. The on-screen graphics and closed caption decoding are done within the
microprocessor, and then sent to the signal processor IC to be added to the main signal.
The chassis utilizes a Switching Mode Power Supply (SMPS) for the main voltage source. The chassis has a 'hot' ground
reference on the primary side and a cold ground reference on the secondary side of the power supply and the rest of the
chassis.
Audio Signal Processing
Stereo
In stereo sets, the signal goes via the SAW filter (position 1002), to the audio demodulator part of the UOC IC 7200. The
audio output on pin 48 goes to the stereo decoder 7831 or 7861. The switch inside this IC selects either the internal decoder
or an external source.
There are two stereo decoders used:
1. a BTSC DBX stereo/SAP decoder (MSP34X5 at position 7831) for the highest specified sets and
2. a BTSC non-DBX stereo decoder (TDA 9853 at position 7861) for BTSC Economic.
The output is fed to the to the audio amplifier (AN7522 at position 7901). The volume level is controlled at this IC (pin 9) by a
control line (VolumeMute) from the microprocessor. The audio signal from 7901 is then sent to the speaker / headphone
output panel.