Tv Guide On Screen - Mitsubishi Electric LT-37131 Service Manual

MODELS: LT-37131 / LT-37132 / LT-46131 / LT-46231
Air
Cable
in
Matrix SW
Main Tuner (TU-100)
(Cable/ATSC/NTSC)
18
61
IC2K01
43
VIDEO SWITCH
(SUB-Y)
When the TV is powered off it begins a process
called 'harvesting'. There are 2 types of harvesting; one
of which is TVGuide harvesting. During this harvesting
process the TV scans through every channel and searches
for TVGOS data. This data is located in the VBI (Vertical
Blanking Interval). The TVGOS data will be located
somewhere between line 10 and line 25 of the VBI (except
line 21).
The data is provided by Gemstar and is inserted
into the VBI by the broadcaster onto a 'host channel'. A
host channel can be any analog channel agreed upon by
Gemstar and the broadcaster. The data packets are
transmitted several times per day for several hours (This
will vary based on location). The TV must be in the OFF
state for the full duration of the transmission to receive the
data packets in their entirety.
(Example of VBI period - Pin 43 of IC2K01)
1/2 Frame
Line 10
starts
possible data
1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1
Total VBI Period
(Figure 1)
TVGuide On-Screen (TVGOS)
V-SYNC
IC7R05
6 7
SYNC
8
H-SYNC
SEPARATOR
SYNC-PLL
9
SWITCH
1
CONTROL
10
IC7R04
3
MULTIPLEXER
4 15
G+VID
VBI
1/2 Frame
Example
data
If there is no data in the VBI
then either you are not tuned
to a host channel that
broadcasts the data, there is
currently no data being
broadcast, or there is an
upstream problem with the
tuner circuit.
Page 15
SIGNAL-PWB
17
8
GOS-TXD
2
IC7R01
9 24
PIC
7
TS
MICRO
10 25
6
GOS-RXD
1
VBI-DATA-IN
7
3
IC7R02
COMPARATOR
2
When the harvesting begins the TV-Micro
enables the output from pin 43 of the Video Switch (see
figure1). The SUB-Y output of the video switch (IC2K01)
is tapped off and sent to a sync separator where H and V
sync are isolated and sent to the PIC Micro. The sync
signals are used for timing of the control signals sent to
IC7R04. This IC directs charge to a hold capacitor which
establishes the slicing threshold for the comparator based
on the level of the incoming SUB-Y signal. Pin 2 of the PIC
Micro provides a hold function to stabilize the H-Sync
during the vertical blank time. The SUB-Y signal is sent to
IC7R02 where the slicing is preformed. The output of
IC7R02 is serial data and is sent to Pin 1 of PIC Micro (See
figure2). This data is assembled by the PIC Micro and is
then transfered by serial communication lines to the DM
PWB via the TS connector and then to the Xilleon
microprocessor.
(Example of VBI data - Pin 1 of IC7R01)
TIP: A test tape can be created by
recording the channel with the
TVGuide VBI data onto a VHS tape.
The recording must be during the
time that the data is transmitted. It
can be used for the VBI slicing test
on the next page.
DM-PWB
27 51
IC8307
QUAD
UART
26 41
XILLEON
(Figure 2)