Good sound; intermittent picture.

[micky]

Can a tv input signal connection at the input coax connector affect
only the picture and not the sound??


I have a 25" Sharp TV, CRT, that often loses its picture, but never
the sound. (Other than that, the picture and sound are very good.
It's analog and I only use channel 3 and a separate tuner.)

The picture can be restored by bending the co-ax TV input cable one
way or the other. Sometimes this lasts for days at a couple hours
each day. Other times it lasts for 10 seconds. I have a string
attached to the cable. Usually pulling the string, pulling it
tighter, or letting the string go makes the picture come back. I wrap
the string around a drawer knob on my workbench (beyond which is the
tv)., sort of like roping a calf and tying the lasso to the saddle
pommel. This is the closest I've gotten to being a cowboy.

Is it possible that the problem is the co-ax input cable connector or
some part or connection near to that???? I don't see how a bad
connection that early on can interrupt the picture and have no effect
on the sound.

Or is it just a locational coincidence, and the problem has to be
somewhere in the main circuity, after the sound and picture are
separate????

Or in the high voltage? although I would think if it were the high
voltage, I would see the picture start out small, maybe as a pinpoint,
and enlarge when I pulled on the string and restored the picture.
Instead it just appears on the entire screen at once.

Thanks for any help you can give.

 

[Geoffrey S. Mendelson]

The picture can be restored by bending the co-ax TV input cable one
way or the other. Sometimes this lasts for days at a couple hours
each day. Other times it lasts for 10 seconds.

Have you tried replacing the coax? It seems to me for a couple of bucks,
you can avoid a lot of effort if it works.

The antenna connector could be loose, or corroded. If you have any DeOxit,
put a drop on the end of a toothpick and clean the center contact of
the antenna socket. If it's an F connector, which is designed for bare
wire as the center contact use something thinner, like a bent paperclip.

Geoff.

 

[Sylvia Else]

Can a tv input signal connection at the input coax connector affect
only the picture and not the sound??


I have a 25" Sharp TV, CRT, that often loses its picture, but never
the sound. (Other than that, the picture and sound are very good.
It's analog and I only use channel 3 and a separate tuner.)

If by "loses its picture" you mean that the picture abruptly and
completely dissappears, with no effect at all on the sound, I'd say "no".

If that's the effect you're seeing, then I'd suspect an intermittent
fault in the set, either a defective connector, or a dry joint, which
gets nudged so as to form a connection for a while when you tug at the
cable.

Sylvia.

 

[micky]

Have you tried replacing the coax? It seems to me for a couple of bucks,
you can avoid a lot of effort if it works.

I've replaced it in that the guy who gave me the tv had the very same
problem with his coax and his location.

The antenna connector could be loose, or corroded. If you have any DeOxit,

I can get it or something like it.

put a drop on the end of a toothpick and clean the center contact of
the antenna socket. If it's an F connector, which is designed for bare
wire as the center contact use something thinner, like a bent paperclip.

Yes, an F-connector. Okay, I'll do that, but is it really conceivalbe
that a bad connection there will affect the blank out the picture but
leave the sound undamaged? I hope so.

 

[micky]

If by "loses its picture" you mean that the picture abruptly and
completely dissappears, with no effect at all on the sound,

Yes, exactly.

I'd say "no".

If that's the effect you're seeing, then I'd suspect an intermittent
fault in the set, either a defective connector, or a dry joint, which
gets nudged so as to form a connection for a while when you tug at the
cable.

I'll look for that. The TV is so big (25") I need to make a lot of
room on the work bench, and before I do t hat it will work fine for 2
days.

But the clues fropm the two of you should speed things up when I do
try to fix it. Being a basement cowboy is not so great after all.

Thanks, and iI think I forgot to thank Geoffrey. Thanks, G.

 

[micky]

I've replaced it in that the guy who gave me the tv had the very same
problem with his coax and his location.

The very same problem and the very same remedy. He got the picture
back by jiggling or moving the coax.

 

[Sylvia Else]

I've replaced it in that the guy who gave me the tv had the very same
problem with his coax and his location.

I can get it or something like it.


Yes, an F-connector. Okay, I'll do that, but is it really conceivalbe
that a bad connection there will affect the blank out the picture but
leave the sound undamaged? I hope so.

In my experience, as the signal level is reduced on an analogue CRT
television, first the picture becomes grainy, and then, as the signal
gets worse, the picture becomes unstable as well. There is no particular
level at which the picture is gone, it just merges gradually with the noise.

Sylvia.

 

[micky]

If by "loses its picture" you mean that the picture abruptly and
completely dissappears, with no effect at all on the sound, I'd say "no".

Boy, am I stupid. Ifnore my first answer. I thought you described
the problem here. I thought that was the problem when I first posted.

But in reality, maybe the picture is still there. It's just so dark
often nothing can be seen but little blue and red hyphen-shapped
lights blinking on for an est. 20th of a second, and then bliniking
on somewhere else around the screen. Hundreds of them at any one time.

At the same time, when closed captioning is on, it looks perfect,
white and bright and the letters fully formed.

Not tonight, but I recall that sometimes the picture can almost be
seen, like it is night time, with most of it black and maybe part,
maybe the background, very very dark blue or very very dark red,
barely one shade lighter than black. I guess when the real color
isn't blue or red, it just looks like black.

I guess my memory is going. Sorrry.

 

[micky]

TV tuner?

DVDR with tuner and hard drive. In the bedroom.

So is that tuner putting out TV signal on channel 3?

Yes, that's it. .

Or is it putting
out separate audio and video (more likely)?

No. I think it has audio and video outputs on the back of it, but
when I put in the wiring for the other rooms, I didn't think to put in
more than one co-ax line. But it's working fine in the kitchen.
Only this tv in the basement is intermittent. .

Is there more than one
connection between the two?
Audio tuner and separate audio sound system?

No. Everything is on that one co-ax line.

Thanks.

 

[[email protected]]

Can a tv input signal connection at the input coax connector affect
only the picture and not the sound??


I have a 25" Sharp TV, CRT, that often loses its picture, but never
the sound. (Other than that, the picture and sound are very good.
It's analog and I only use channel 3 and a separate tuner.)

The picture can be restored by bending the co-ax TV input cable one
way or the other. Sometimes this lasts for days at a couple hours
each day. Other times it lasts for 10 seconds. I have a string
attached to the cable. Usually pulling the string, pulling it
tighter, or letting the string go makes the picture come back. I wrap
the string around a drawer knob on my workbench (beyond which is the
tv)., sort of like roping a calf and tying the lasso to the saddle
pommel. This is the closest I've gotten to being a cowboy.

Is it possible that the problem is the co-ax input cable connector or
some part or connection near to that???? I don't see how a bad
connection that early on can interrupt the picture and have no effect
on the sound.

Or is it just a locational coincidence, and the problem has to be
somewhere in the main circuity, after the sound and picture are
separate????

Or in the high voltage? although I would think if it were the high
voltage, I would see the picture start out small, maybe as a pinpoint,
and enlarge when I pulled on the string and restored the picture.
Instead it just appears on the entire screen at once.

Thanks for any help you can give.

If I recall correctly, as the modulation gets stronger, the picture
gets darker. Of course the tuner/IF system had AGC, which will try to
maintain an adequate signal output as the strength of the input signal
changes. And some sets were designed to blank the screen (or put up a
blue screen) if the input signal was below adequate levels. However,
I can't see any reason to believe that that is happening in this case.

By far, the most likely situation is that there is a bad solder joint
in the video processing area AFTER the audio subcarrier is extracted.
Given the level of integration in modern TVs, the tuner and IF strip
could be integrated into a single mackage. As such, it is unlikely
that replacing the RF input would fix anything.

By the deacription, it's unlikely it's the high voltage.

There are a number of sources for schematics and even complete service
manuals online. One of the better ones is Elektrotanya.com.

PlainBill

 

[Sylvia Else]

Boy, am I stupid. Ifnore my first answer. I thought you described
the problem here. I thought that was the problem when I first posted.

But in reality, maybe the picture is still there. It's just so dark
often nothing can be seen but little blue and red hyphen-shapped
lights blinking on for an est. 20th of a second, and then bliniking
on somewhere else around the screen. Hundreds of them at any one time.

At the same time, when closed captioning is on, it looks perfect,
white and bright and the letters fully formed.

You said the previous owner of the television was seeing the same
behaviour. Did he also have what is now your DVDR unit connected?

It's not clear what role the DVDR unit is playing here. If it's tuning
an analogue channel, and just frequency shifting it, then the closed
captioning would have to be generated by the TV. In that case, there is
clearly a fault somewhere in the between the TV's own tuner, and where
the closed captioning gets superimposed on the picture.

On the other hand, if the DVDR unit is tuning a digital channel, and
providing an analogue output, complete with closed captioning, then it's
hard to see that there can be anything wrong with the TV at all, with
the problem lying in the DVDR unit, which is, after all, connected to
the other end of the coax that you waggle.

Not tonight, but I recall that sometimes the picture can almost be
seen, like it is night time, with most of it black and maybe part,
maybe the background, very very dark blue or very very dark red,
barely one shade lighter than black. I guess when the real color
isn't blue or red, it just looks like black.

That really sounds to me as if the DVDR unit is just frequency shifting
an analogue channel, and that there's a faulty connection or dry joint
in the video signal path in the TV - a small amount of the signal gets
through by the capacitance of the failed connection.

Sylvia.

 

[micky]

You said the previous owner of the television was seeing the same
behaviour. Did he also have what is now your DVDR unit connected?

My own exact DVDR? No. He was a stranger who gave the TV to me via
Freecycle. He just said the picture went out peroiodically and he
got it back by moving the cable that went into the TV.

It's not clear what role the DVDR unit is playing here. If it's tuning
an analogue channel,

I have no analogue channels, just over the air channels.

and just frequency shifting it, then the closed
captioning would have to be generated by the TV. In that case, there is
clearly a fault somewhere in the between the TV's own tuner, and where
the closed captioning gets superimposed on the picture.

On the other hand, if the DVDR unit is tuning a digital channel, and
providing an analogue output, complete with closed captioning, then it's
hard to see that there can be anything wrong with the TV at all, with
the problem lying in the DVDR unit, which is, after all, connected to
the other end of the coax that you waggle.

Yeah, but I have 3 other TVs I watch daily that never have problems

The bad one is in the basement, the good ones in the bedroom, the
bathroom, and the kitchen. The DVDR is in the bedroom.and the
bedroom tv gets the signal first. Then the basement TV with the
problem, after after that the signal goes to the kitchen TV which has
no problems.

(There's an amplified splitter that sends the signal to the bathroom
and the bedroom/office, but the computer is broken so I spend a lot of
time in the basement trying to fix it and using a basement computer)

That really sounds to me as if the DVDR unit is just frequency shifting
an analogue channel, and that there's a faulty connection or dry joint
in the video signal path in the TV - a small amount of the signal gets
through by the capacitance of the failed connection.

What I can do to test this is try to watch a movie on the VCR, which
sits next to the DVDR and is connected in parallel by an A-B switch.

I also have a digital conversion set-top box feeding the VCR, so maybe
I'll just watch television via the box/VCR. I'll do that tonight.

Sylvia.

Thanks a lot.

 

[micky]

If I recall correctly, as the modulation gets stronger, the picture
gets darker. Of course the tuner/IF system had AGC, which will try to
maintain an adequate signal output as the strength of the input signal
changes. And some sets were designed to blank the screen (or put up a
blue screen) if the input signal was below adequate levels. However,
I can't see any reason to believe that that is happening in this case.

By far, the most likely situation is that there is a bad solder joint
in the video processing area AFTER the audio subcarrier is extracted.
Given the level of integration in modern TVs, the tuner and IF strip
could be integrated into a single mackage. As such, it is unlikely
that replacing the RF input would fix anything.

By the deacription, it's unlikely it's the high voltage.

There are a number of sources for schematics and even complete service
manuals online. One of the better ones is Elektrotanya.com.

I noted each point you made, both exclusions and leads. . I didn't
knjw about Elektrotanya.

Thanks!