Strange TV

Page 1 of 2  
Not sure this is the right place to post this but perhaps someone here will have an answer. I have two TVs on both cable and satellite. I have a local Public TV Channel that occasionally has no sound on one TV. Picture is OK but no sound. The sound on the other TV is just fine. I can use the VCR as a tuner and the sound is OK. Another problem I've noticed is when watching the NBC nightly news on a local NBC station via cable, the sound is not sycronized with the speakers mouth. It's OK on the other TV or if I use the VCR as a tuner. This only occurs when on cable and not the satellite. Both TVs are on the same cable feed. Anyone got any ideas what's going on?
Don in Tracy, Calif.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The symptom of a cold solder joint. The sound circuitry is good. A good old slap on the TV cabinet should bring the sound back temporarily. The TV heats up and cools everytime you switch it on or off. That causes expansions and contractions and weak solder joints do lift from the PCB, or generate hairline cracks.
If you are handy with a solder iron and willing to poke around the innards open up the back cover, with the power disconnected of course. With the power on again, you should have video and perhaps audio. Use a wood dowel or some non conductive stick to wiggle the wire cabling. If you get lucky the audio cable (or component eg. volume control, speaker connection) cold solder should show up. Take a close look at the solder joints, especially where the plug pins are soldered onto the PCB.
Don't be too nervous about the high voltage. Normal precautions should suffice. If you do get zapped it is unpleasant but you don't see any TV techs with frazzled nerves or burnt hair walking around. In an earlier life servicing computer monitors and equipment I had been zapped only once.
This this how I fixed my TV's problem with intermittent video problems. The top few video scan lines would spread out every now and then particularly when the furnace fired up in winter. I opened up that hernia box quite a few times over the years to locate the fault without success. It was frustrating as I could not reproduce the problem at will, thus bringing that monster box to the repair shop would be pointless. Furthermore all the electronics was on one PCB and the wiring-packaging was too compact to allow meter probes to reach the test points. On the last try, I happened to brush against the cable and the video problem appeared. Jiggling that cable harness reproduced the problem consistently. The rest was easy.
Anything more than locating and resoldering the cold solder joint is probably a shop job. There are hardly any home repair replaceable electronics components nowadays. Ask for a repair estimate first. If your TV is more than five years old it has probably more than paid for itself and not worth repairing. Its cheaper and better to by a new TV.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The feeds are delayed by the process of sending it to the satellite and back, or in coding electronics. So, one is a few seconds (or a fraction) ahead.

There are many problems that could cause it. <snip>

It's mostly unpleasant. If you happen to be unlucky, it can be fatal.
People arn't born knowing the proper precautions.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 16 May 2004 11:03:28 GMT, Ian Stirling

If the video and sound both go to the satellite and back, they should be delayed the same amount. I never noticed this (even with satellites) in the days before digitizing video - only after digitization, so I think it is because of that.
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The television network has fragmented, and there are now many more ways of getting TV to the end user than there once were. Encoding or recoding the signal to do statistical multiplexing (if you can look ahead several seconds, you can fit n channels into a given bitrate at better quality than if you just encode them all with minimal delay.
This introduces a several second delay.
Sometimes this is counteracted by adding in delays to other signals, to make them happen more or less in time.
A hop to a GEO satellite and back takes only .2 seconds or so. Even 2 hops only adds .5 seconds.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 16 May 2004 21:02:06 GMT, Ian Stirling
It would be OK if they kept the signals in sync.
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

They do. Sound and vision is always in sync on every broadcast channel The problem is that how do you sync different channels.
If someone's listening to an FM broadcast of a sports event, and happens to turn on a satellite TV, there may be a delay of up to around 10 seconds.
Do you delay the FM signal by 10 seconds? And what if there is a digital cable station getting its feed digitally from that satellite, and reencoding. This may add another 5 seconds, so do you up the delay to 15 seconds?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 17 May 2004 11:58:10 GMT, Ian Stirling

Well, the sound and video are out of sync when they get to my house, and I'm not using SAP (just a single channel).
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If they are, then report it to your supplier, it is a fault.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 18 May 2004 11:36:28 GMT, Ian Stirling
At the house I lived at two years ago, I had the cable gut come out. He saw the problem but said that there was nothing he could do about it.
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Here is the device to get them back in sync http://www.tek.com/site/ps/0,,25-13988-INTRO_EN,00.html that was mentioned in http://www.tvtechnology.com/features/production-manager/f_cj_production_manager-03.19.03.shtml
but one of the devices has to be used before they get out of sync and another at the end to get them back in sync. So would CNN (say) have to use one before the audio and video get out of sync, and then the local cable company have to use one to get it back in sync?
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It turns out that is the reason:
"...However, the nature of the sync problems TV is having is just the opposite: The video lags the audio. That's because of digital processing.
"There's a long and a short reason for this; you'll be happy to know that I'm only able to recite the short one: The process of digitally encoding and decoding video is more complicated than for audio, and so it takes longer. Running through a number of encoding and decoding processes where it always takes video longer to make the trip than audio, and the problem gets worse.
... Lip sync on the TV station was correct; on the cable channel it was badly out of sync.
...the problem won't get solved unless you insist that it is. Declare war on lip sync problems and get them fixed. "
Quoted from:
http://www.tvtechnology.com/features/production-manager/f_cj_production_manager-03.19.03.shtml
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 17 May 2004 19:48:43 -0400, Jud McCranie

The technical discussion is getting confusing.
I had taken courses on TV servicing for interest (though never used that professionally as there is no money in consumer electronics servicing.) If you refer to any textbook, the front chapters with the basic concepts will do, there will be a block diagram on TV circuitry and on the TV broadcast signal.
On the analog TV sets. The audio and the video are embedded in the same signal - the composite video signal. The signal gets into the TV set via the antenna or the cable to the "Tuner" block where you select your channel. Then it enters the "IF Strip" block followed by the "Video Detector" block. From here the signal is split and output to the "Audio" block and the various "Video" blocks. The signals may be distorted, or missing audio or video only. But there is no way one signal will be out of synch with the other.
I haven't read up on digital TV circuitry but a quick search on the Internet turned up < http://www.sencore.com/custsup/pdf/TT171.pdf and there is a useful block diagram in page 2. It is still a single composite video signal which does not get separated into its audio and video components until the second PIF stage (cable ->Tuner -> PIF -> etc.) and therefore both the audio and video arrive in synch and cannot be out of synch whatever happens inside the TV set.
A few select descriptions from this URL will be useful:

From my understanding of the above Sencore explanation digital TV is not true HDTV as HDTV will be wholly digitized at the broadcast end.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Don wrote:

In a similar vein...
We use Comcast cable for TV, Telephone and Internet service.
I have noticed that about once a week, particularly when watching TV "Premium Channels" or "On Demand" programs there is a high pitched "chittering" background noise on the audio, characteristicly like an "automatic level control" system (It increases in level when the program audio is quiet and noticably decreases when, for example, an actor starts speaking.) It's reminiscent of "alternator whine" on an AM car radio twenty years ago.
The noise sometimes persists for as long as 15 to 30 minutes, then it goes away. If I switch the cable box around to to a few other channels when the noise is present, there isn't that background noise on any of them.
Unless I'm really engaged in the program (Like sometimes it's SWMBO who'se watching it, but I'm reading the newspaper in the same room.) that damn noise starts boring through my brain and is hard to "tune out".
Last night we were watching a pay "On Demand" movie and that annoying audio noise was present for about half the movie. I found myself getting irritated at having to put up with it, particularly as we were "paying extra" for the program.
I've called Comcast's customer service about it, but they act like they don't understand me. (Big suprise.)
Anyone else experienced this particular problem, and got it fixed?
Jeff
--

Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can smile when things are going wrong, you've thought of someone
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I have that on most channels, some are worse than others. My guess is that it is caused by the video signal being compressed for transmission and de-compressed. It takes time to do the compression/de-compression, and they don't bother to keep the sound and video in sync.
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jud McCranie wrote:

But why do I have one TV that is OK and another one that is off sync. They are both coming from the same cable feed.
Don in Tracy, Calif.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I don't know. For me it seems to vary by channel and may be better or worse at different times. I had the problem with my old house in a different city, and different cable provider too. And I've seen the same problem in motels I've stayed in.
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jud McCranie wrote:

Swap the TV's and see if the problem stays with the TV or stays at that location. 99.9999999% odds are that it stays with the TV. Are you SURE it's not set to SAP? From the way you answer, it sounds like you might not even know what it is.

Hmmmmm, I see.
You may want to seek professional help.
--
TP / Network Man __________________________________
If u want the races for free,
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

He should try watching TV with aluminum foil wrapped tightly around his head!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I think his sync problem is real, but I don't know why it would be in one TV and not the other. Some channels are worse than others, and here locally-inserted commercials are even farther out of sync.
--
Replace you know what by j to email

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.