Philips 20PT643F Service Manual page 81

Figure: Mono Carrier solder side
The 'L01.1U AC' 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 Mono Carrier.
The microcomputer communicates with the memory IC, the customer keyboard, remote
receiver, tuner, signal processor IC and the audio output IC via the I C bus. The
2
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.