Weird horizontal white bands/streaks scrolling up the screen (Ground Loop) - AVS Forum
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post #1 of 8 Old 04-03-2008, 10:18 AM - Thread Starter
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I have a new LG 32 inch plasma EDTV, and I'm getting whiteish grey horizontal bars scrolling up the screen from the bottom to the top, repeatedly. I have searched this forum and this appears to be the standard "ground loop" issue described elsewhere. There are a couple of odd inconsistencies though, and I'm looking for some advice.

My TV is plugged into a 3-prong outlet and thus grounded there. My digital Cable Box and my DVR are also plugged into the same outlet, but they are 2-prong connectors. They also each have RF/coaxial cable coming into them from the cable company, and so those two devices are grounded by the RF cable instead.

If I connect the cable box to the TV via standard Composite/RCA/AV video cable, I get the grey scrolling horizontal bar hum, the usual symptom of a ground loop. BUT..

Inconsitency #1: If I instead connect the cable box to the TV using an RF cable, there is no problem! The scrolling streaks only occur when using an composite/AV video cable to connect the two devices. If the problem is a ground loop, shouldn't it occur either way, regardless of what type of connection cable I use *between* the two? And...

Inconsistency #2: Connecting my DVR to an RF modulator via AV video cable, and then from there to my old CRT television (only has RF input) causes no problem whatsoever. But if I use my new plasma TV in the *exact* same configuration, I get the scrolling ground loop hum bars. If it's a ground loop, shouldn't it occur regardles of which TV set I'm using? Or, is that because my old TV is 2-prong and so it's not grounded at the electrical socket?

As for solutions, what's the simplestway I can solve it? Can I buy a power bar/surge protector with at coaxial/RF connection, run my cable through that, and cause it therefore to be grounded at the same place as my plasma TV, assuming I also connect that to the same power bar?

Any help is greatly appreciated, thanks!
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post #2 of 8 Old 04-03-2008, 10:29 AM
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For the composite vs. RF scenario, the RF paths into most televisions include something called a "balun", a balanced to unbalanced transformer that technically breaks the ground connection ---> no ground loop.
The composite input will not have such a transformer.

This is likely true for your other "test" as well in some fashion.

This topic was just recently covered in another thread about a week ago. the solution is there. Check post #3908 of this thread:

http://www.avsforum.com/avs-vb/showt...0#post13449490

TW

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post #3 of 8 Old 04-04-2008, 02:28 PM - Thread Starter
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For anyone's future reference, using a power bar with coaxial cable input successfully solved the problem. The scrolling grey bars disappeared completely. I used a Monster 1110 joule power bar/surge protector.
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post #4 of 8 Old 05-21-2008, 01:36 PM
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LOL!!! From post #3908 of the above-mentioned thread:
Quote:
I have the same situation and just ended up rolling a small blanket and tucking it along the right edge between the tv and the wall (most of my buzzing comes from the right side)...it doesn't block the fan or anything like that...I've forgotten it buzzes anymore...a conditioner for me did nothing...

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post #5 of 8 Old 05-22-2008, 09:37 AM
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If you have any cable splitters in your house it would also be prudent to properly ground those. Also consider any light dimmers you have and try switching them off to see if it makes a difference. If it does, considering replacing the dimmer with a switch.
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post #6 of 8 Old 05-22-2008, 12:51 PM
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The reason the "Monster 1110 joule power bar/surge protector" worked is that it connected the coax ground and the TV ground together putting them at the same level.

The issue is more than likely outside of your house. Check the grounding where your cable enters your home and make sure its good.

It can also be that your entire electrical system is not properly grounded (if this is the case its probably due to the age of your home/electrical system).

One of my friends had this same issue (white scrolling lines) and it turned out to be that his entire electrical system was not properly grounded due to corrosion.

Also, as an FYI, you will probably want to stay away from "ground breakers" due to their high frequency cutoff. They can make it so you can't tune in some channels (which in my friends case was about 5-6 HD channels).
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post #7 of 8 Old 05-22-2008, 04:44 PM
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Quote:
Originally Posted by JS23 View Post

Also, as an FYI, you will probably want to stay away from "ground breakers" due to their high frequency cutoff. They can make it so you can't tune in some channels (which in my friends case was about 5-6 HD channels).

This is why I specify the VRD-1FF from www.Jensentransformers.com
It is not cheap, around $60, but has a very low insertion loss and response out to 1 GHz, plenty of headroom for Hi Def CATV

TW

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post #8 of 8 Old 09-22-2008, 09:45 AM
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The VRD-1FF from Full Compass eliminated all of my horizontal hum bars in my TV system. The hum bars being generated from time to time by Cox Cable.
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