Max said:
So let me see if I get this right, broadcasters are sending signals to
my television to disrupt programming I am paying for?? I don't follow.
Well, since I opened the door, here's a much better explanation and it
doesn't put you any further ahead but, at least you'll understand
what's happening:
THOMSON AUDIO DROP-OUT
There has been a situation when in some RCA/GE televisions a low-level,
scratchy-sounding noise comes out of the speakers instead of normal
audio, or when video is muted. These problems can occur when invalid
XDS data is broadcast by television stations and received by certain
Thomson television receivers. XDS data is digital information placed
within the video signal's vertical interval of an analog (NTSC)
television transmission. This data is used by the microprocessor in the
television receiver. It may be transmitted from any analog television
channel.
_________
Explanation of XDS data:
In each frame of video, line 21 contains a single stream of data,
containing different types of data packets. Field 1 of line 21 contains
two captioning channels (CC1 and CC2) and two "text" channels (TEXT1
and TEXT2). All four of these data channels share that 600 cps data
stream, and the information is sorted out using packet headers. Field 2
contains a matching set of data channels (CC3, CC4, TEXT3, and TEXT4),
and can also contain extended data services (XDS) packets.
The XDS (extended data services) provide information about the current
program, TV station, and network. Unlike the caption and text data,
they are packets rather than continuous streams of data.
XDS packets include:
Name, length, and start time of current show
Type of show, based on a set of category codes
Program content advisory (see "V-chip data" below)
Network name
Station name and number
Time of day
National weather service warning codes
________
The "Thomson audio drop-out problem" occurs when a broadcaster sends
invalid XDS data - that is, data that does not contain truncation
packets. There are certain XDS encoders on the market that broadcasters
may use that will do this. Thomson television receivers using 16-bit
microprocessors (i.e. CTC197/PTK195 chassis) are programmed to decode
XDS data by counting data packets. When the microprocessor encounters
corrupt data with no truncation packets, the data overflows into memory
registers where it does not belong, the first of which relate to the
audio processing. When the microprocessor encounters this corrupt data
in the audio (or even video) registers, it interprets it as the start
of a shut-down, and mutes the audio (and/or video).
When the unit is unplugged and replugged, it empties these registers of
the corrupt data.
It is good to know that this problem was resolved in newer chassis
designs that use 32-bit microprocessors (i.e. MM101/102 and
DTV306/307).
But the vulnerable Thomson televisions will do this as they are
receiving invalid data from a station to which the MAIN TUNER is tuned.
This is why it is so important to find out what channel, and more
specifically, what program the viewer was watching at the time of the
anomaly.
The real solution:
Broadcasters can upgrade their equipment so that the data they send is
valid (includes the necessary truncation packets), so that their signal
is always 100% valid, and does not mess up these Thomson receivers.
Some retailers have someone assigned to contact suspected broadcasters.
Once the customer identifies the program (or commercial) was being
watched (including the time of day) when the incident occurred, they
should report it to the home service specialist.
A final note:
XDS data may be inserted live, or played back on video tape by a
broadcaster. It can also show up on a VHS tape that the customer
recorded from a previously-aired television program.
www.techdata-kicksass.net
