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Discussion Starter · #1 ·
My Dish TV signal is connected via S-cable directly to a Panasonic 711XU projector’s S-cable input (not using HTPC yet).


The image contains a faint horizontal line that starts at the bottom of the screen and floats to the top. A new line is produced every few seconds.


Yet it does not occur when watching DVD’s. The DVD player is also connected directly to the projector via component breakout cable to the projector’s VGA port.


Normally, I would guess the S-video cable is picking up interference from somewhere. But I don’t believe the cable crosses any other cable.


Any guesses what causes a projector to produce a floating line from only a certain source?
 

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Sounds to me like you have a bad connection somewhere. I think that it sounds like a loss of signal strength rather than interference but I could be wrong. Anyway, the most likely culprit is the coaxial cable running from your dish to your satellite receiver. It's usually a very long run and they tend to use cheap cable when installing it.


If satellite is your only source giving you problems start by replacing the ends on your coaxial cable. If that doesn’t work you might have to replace the entire run. I’ve seen cases where part of the sleeve has been ripped off of the cable by a nail or other sharp object.
 

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The symptom you are describing is most often associated with a problem called "ground loop". It could be caused by powering the satellite receiver from a different AC wall circuit than the projector (or powering the LNB on the dish from a seperate circuit via a "wall wart" type power supply). It could also be caused by the telephone line connected to your receiver. The moving line is most likely the result of another device like a computer or electric motor injecting electrical noise into your AC power - I had a similar problem due to a large attic fan near my antenna distribution amps.


Try momentarily disconnecting the phone cord from your receiver, if the problem goes away, get a telephone circuit ground isolator. If the problem persists, plug the telephone back in and try a cable ground isolator on the coax connection to the receiver. (This assumes you DO have a seperate "wall wart" supply for the LNB, and isolating the cable will not block the DC power coming from the receiver to the LNB, another possibility.) You will need a ground isolator rated for a 2Ghz bandwidth for the frequencies involved (somewhat harder to find than the more common types used for VHF/UHF/cable frequencies).


Gary
 

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Discussion Starter · #4 ·
Thanks for the suggestions. I’ll check the coax cable for damage. But since I didn’t have the floating problem when it was connected to a regular TV, I doubt that would be the cause. BTW, the run from the dish to the receiver is fairly short, maybe 15’.


On Gary’s ground loop theory…if I understand you correctly, you want the receiver and the projector to be connected to the same wall circuit? OK, I’ll try it later.


I believe the sub-woofer is connected to the same outlet as the receiver. Wonder if that could be the cause?


I hope that is the problem because your other theory…that it’s related to a phone line connected to the receiver…doesn’t apply. I do not have the phone line connected to the receiver.


Thanks again for the suggestions. I’ll try ‘em later tonight.
 

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Gary is almost certainly correct - this is a classic case of a ground loop. One thing to try is to put a ground defeater (commonly referred to as a cheater plug or 3 prong - 2 prong adapter) on the offending pieces and see if it goes away. But that is a diagnostic tool, NOT A SOLUTION. You never want to leave the ground defeated for safety purposes. Try it and report back if you need more help.
 

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Discussion Starter · #6 ·
Here are last night’s results in trying to cure the floating line problem.


First, examined my expensive s-Video cables. Observed a sloppy soldering job in both connectors, with one wire in each end barely making a connection (would anyone recommend I re-solder those wires, exchange the cable, or just leave it alone)?. But when I tried the same S-Video cable on my DVD player, the horizontal line did not appear. So it’s not the cable.


Next, tried using a 3-to-2-cheater plug. Tried it on each of my system pieces. Problem did not go away.


Next, tried powering each of my system parts in different outlets. No improvement.


Last idea..this one from Gary McCoy I powered up the projector and the satellite receiver from the same outlet. Voila! Thanks Gary! I never would have thought of that on my own.


It is not intuitive to a layman like myself that powering system parts from the same outlet is necessary to prevent ground loop. I was thinking the opposite…that using the same outlet for different components could create some type of interference (wondering why it is that no one in projector-land has strongly urged everyone to use the same outlet?).


I would appreciate if anyone could explain in simple terms why using the same outlet prevents a type of banding.


Thanks to all you experts on AVS. You saved me from an unnecessary service call!
 

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Quote:
Originally posted by wolfgang armbru
Next, tried using a 3-to-2-cheater plug. Tried it on each of my system pieces. Problem did not go away.


Last idea..this one from Gary McCoy I powered up the projector and the satellite receiver from the same outlet. Voila! Thanks Gary! I never would have thought of that on my own.


I would appreciate if anyone could explain in simple terms why using the same outlet prevents a type of banding.
Did you put cheater plugs on all the equipment at the SAME time?


It is usually not a matter of plugging into different outlets, it is a matter of plugging into different outlets that are on different circuits in your electrical panel.


There is always a certain amount of resistance to current between grounding points. "Absolute ground" does not exist, but nevertheless, that is what A/V components are "looking for". When you have two audio/video components connected to different circuits (grounding points), the difference (voltage differential) between the circuits can be enough to cause things like video hum bars or audible hum through your loudspeakers. It is also sometimes referred to as the grounding differential.


Do not take this to mean that you should never connect your components to different circuits. This is often done and is sometimes desirable when you need multiple circuits due to multiple power amplifiers etc. There are ways to wire a house to reduce the likelihood for ground loops and there are also measures (other than plugging everything into the same circuit) that can be taken after the fact to eliminate them and in many instances there are no problems, even if no special precautions have been taken.


Speaking generally, ground loops are a fairly common problem.
 
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