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micky micky is offline
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Default Good sound; intermittent picture.

On Thu, 03 Nov 2011 10:53:34 -0700, wrote:

On Tue, 01 Nov 2011 02:54:51 -0400, micky
wrote:

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.


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

Thanks!

PlainBill