Tuning; Over Current Protection; Teletext Display - Daewoo DDT-21H9ZDF(21") Service Manual

5-4-4 Tuning

The AFC information is supplied by the demodulator IC, and becomes available on VCT pin 7 for controlling software.
The controlling software uses this information for tuner frequency tracking ( automatic following ). The AFC window
is typically between 50 KHz and 100 KHz.
The minimum frequency step of the tuner is 50 Khz.
This AFC function is disabled when a program is tuned using the direct frequency entry or after fine tuning adjustment.
Therefore it is recommended to tune channel with the TV search function ( manual or ATSS ) or using the direct
channel entry to enable the Automatic Frequency Control.

5-4-5 Over Current Protection

In case of overload, the collector voltage of TR Q801 will be rise. The voltage on pin 7 of microcontroller rises over
reference voltag e (about 1.5 V )The controlling software which continuously monitors this voltag e will switch the set to
stand by mode. To power on the set again the user must switch it off using the main power switch. Appropriate hyster-
esis guarantees a reliable operation.

5-5 Teletext Display

National character option bits C12, C13, C14 are transmitted in the page header of a given teletext pag e. The national
option bits are intended to change (or exchange) 13 characters within the G0 character set, according to the needs of
each national language. However, for Cyrillic and Greek languages, a major character set change (a change of character
mapping) needs to effected for correct display
These codes represent, for a given broadcaster, the intended language that the teletext page should be displayed in. As
there are only 3 bits, there are only 8 codes available to cover all the possible language combinations. This means that
for a received code there are several possibilities meanings, and therefore several possibilities for display.
This is not as bad as it first seems, as we use the user-selected OSD language to identify the intention of the broadcaster.
For example, a user wishing to see Russian teletext should select Russian OSD language, otherwise he would not have
correct teletext display on the TV.
The table below allows the reader to understand the relationship between selected OSD language (which is under user
control), the teletext language display (selected by national option bits in transmission page header) and the language
mapping (either Latin or Greek/Cyrillic)
An example: For Greek teletext display, (if national option code 1 1 1 is received from the broadcaster), the user should
select the Greek OSD language. Even if English, French, German, Italian, Spanish, Dutch, Danish, Finnish, Norwegian
or Swedish OSD languages are selected, the teletext will be correctly displayed.
However, if Polish, Hungarian, Czech, Slovakian, Rumanian or Russian OSD are selected, Latin font mapping is
selected. The consequence will be incorrect teletext display, with NO GREEK CHARACTERS DISPLAYED. Roma-
nian national font options will be selected.
-48-
Service Manual CP-099/FS