Philips PTV800, Service Manual

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Guide Plus - Smart Clock
Guide Plus or Gemstar is a menu-driven broadcast information service broadcast on ABC
affiliate stations.
( Figure 4) TV guide company provides the service which contains information
similar to their weekly magazine. The free service provides two to three days of programming
per download. When the set is turned off, the set tunes to the ABC affiliate station,
downloading Channel Guide information when it is broadcast. The data is serially transmitted
during the vertical blanking interval. The complete data transfer takes about two hours.
Smart Clock downloads Time information from the local PBS affiliate when the set is turned
off. Both the Smart Clock and Guide Plus must be set up in the menu before they will work.
Sets with Guide Plus and Smart Clock are required to keep the power supply turned On, to
supply power to the Tuner and IF circuitry while downloading information. Guide Plus and
Smart Clock download information while the set is turned off. To accomplish this, the
Microprocessor, IC300, Pin 52, remains low, when the set is turned off to keep the Power
Supply turned on. The HS line on Pin 2 of IC300 outputs a Low, turning Transistor Q403 Off.
This removes the Low from the base of Q400, which keeps it turned off, during normal
operation. Q400 is now turned on by the 5 volt Standby Supply through resistors R433 and
R429. This turns Q400 On, switching resistor R482 to Cold ground putting it in parallel with
R454 and R455. This changes the biasing of the feedback circuit for the 130 volt source. This
biasing change causes the 130 volt source to increase to approximately 145 volts. Since the
load is removed from the 130 volt supply, it is necessary to increase the output voltage to 145
volts to maintain the secondary voltages, 15 volt, 9 volt, -32 volt, 32 volt and the Audio Power
Source at the correct voltage.
In addition, the Low on IC300, Pin 2, also turns off transistor Q635 in the Horizontal drive
circuit. This removes the pull up resistor, R624 from the Horizontal Drive Circuit. This allows
Pin 8 of IC600 to go high removing Horizontal Drive. With no Horizontal Drive, Q501
(Figure