Rolling shadows on my TV

[Kristian]

Hi folks

I recently moved, reformatted, installed all over and so on. Now when I port out image through the g400 to my TV (DVD, clone etc.) I get some rolling artifacts on the TV. It looks as thick lines of shadows that slowly drifts to the top of the screen and then starting all over again.
I cant figure out why, also Im not sure if this is right but my TV runs at 100Hz and the monitor at 85Hz - could I port out a 100 Hz signal to the TV?

Otherwise, what do you think migt be the problem? I use S-video out to the tv...

Kindest regards

Kristian

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Striving for perfection

[Brian Ellis]

Kristian

My guess, with a 90% certainty, is that you have a 50 Hz power frequency causing this and your video is not synched to the power frequency. There are two possible causes: the most likely is that you either have a ground loop in your cabling or the screening (shielding) in a cable is defective and running not too far from a power cable; the other is that your TV has a 50 Hz component added to either the video signal due to defective smoothing of a power supply or even to the EHT accelerating voltage on the tube or toob, as our US friends are wont to say.

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Brian (the terrible)

[Kristian]

Ok!

So what should I do then? Try to isolate the s-video cable as much as possible (will it help) or should I put down some money on a more expensive shielded cable?

Any tips welcome....

Kristian

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Striving for perfection

[Brian Ellis]

Kristian

As a general rule, it is rare for an expensive cable to work any better than a cheap one. This is a myth perpetrated by those cable makers who wish to see buyers waste their money. (There are exceptions).

To check for ground loops: disconnect every cable in your system except the video. If it improves it, it must be that your audio shielding is causing the problem: disconnect it from the connector at the far end from the source. Keep all power cables as far as poss from the video. Put the BOB as far as poss from the computer and certainly nowhere near the computer PSU. Etc.

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Brian (the terrible)

[Kristian]

I found the cause...it is my antenna-cable. When I disconnect it from the TV the shadows die away. But what can I do now? Disconnect the antenna when watching DVD's some might say - but that isn't really a solution....

regards

Kristian

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Striving for perfection

[Brian Ellis]

Kristian

OK, I see a little clearer now. It sounds like your antenna system may be grounded somewhere, causing a loop. If you are on a cable or shared (e.g. apartment block) system, there is little you can do directly (see below). If you have a simple passive antenna, make sure your cable and active antenna elements (the dipoles) are nowhere grounded. If you have an active antenna (e.g. with a booster amplifier or going through a VCR), try reversing the polarity of the power plug feeding it and/or remove any grounding in the system: it may work.

If all else fails, try a wideband isolating transformer as close to the TV as possible. I don't know whether these are commercially available, but they are easily made by an electronics engineer (they consist of a two windings of a few turns of wire on a ferrite core - simplified description). This will introduce a few dB of loss, so you may see a slight increase of noise on weak signals. If all your signals are strong and you cannot obtain a ready-made isolating transfo, then you could put two 600-75 ohm transformers for balanced to coax feeders back-to-back: these should be obtainable in any TV shop for a buck apiece. Just join the balanced side of them together, plug your antenna cable into one coax plug and the other into your TV set (you may need to change the gender of a coax sug or plocket).

Hope this helps.

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Brian (the terrible)

[IvanP]

I have had exactly the same problem that started one year before. I've found the same source: Antene cable. (We have shared cable system.)
There should be something with ground because if you disconnect ground on the antene connector the picture is OK. If your signal is strong enough it can be the solution for you. (Unfortunatelly not for me.)

Ivan