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Godfather
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495 Posts
Discussion Starter · #1 ·
I have computer with an ATI All-In-Wonder connected to a 27 inch TV. I basically use this computer to watch AVIs using the ATI software. Recently, I got back into Starcraft, and the small VGA resolution of the game is perfect for the TV! I did notice that I started getting these diagonal lines on the TV. They may have been there before, but the dark screens of the game got my attention.

I've searched here and it seems it may be a ground loop problem. How would I go about getting rid of it?

My current config:

From wall, I have a 6 socket Power Strip with:
- TV
- DVD/VCR Combo
- CPU

From computer to TV, these are the connections:
AV from CPU >>> Line 2 Input of DVD/VCR Combo >>> Line 2 Input of TV (All Composite)

==========================

Other info:

I have my 622 TV2 from the living room (25 ft composite) connected to the Line 1 of the DVD/VCR Combo, but I don't get the diagonal lines. I also have a DirecTV Input on the Line 1 of the TV (another 25 ft composite), and I also do not get the diagonal lines.

Hope you guys can help me with this. Thanks.
 

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Old Guys Rule!
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5,053 Posts
If the problem were a ground loopp, I'd expect to see "sound bars" on the TV or a wavy picture. The diagonal lines sound like retrace lines to me. Do you see them on your monitor as well? Is the distance from your computer to the TV also 25 feet? Is it necessary to adjust brightness and/or contrast when viewing thc omputer output on the TV? You didn't say if you'd tried hooking the AIW output directly to the TV, eliminating the DVD/VCR. Your problem could be inadequate signal strength
I have a computer with an AIW card installed, but haven't tried the composite outputs on it.
 

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Godfather
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495 Posts
Discussion Starter · #3 ·
The diagonal lines do not manifest if I connect the CPU to an actual monitor (17 inch LCD). The CPU is below the TV, so that cables I am using is no more than 6 feet.

I don't normally touch the brightness/contrast controls on the TV when switching video sources.

I'll try putting the AIW directly to the TV tonight to see if that solves it. Thanks, cholly.
 

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Godfather
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495 Posts
Discussion Starter · #4 ·
I connected the PC directly, and although the lines are not as bad, they are still present. I'll probably see if a good UPS can get rid of it.
 

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Hall Of Fame
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3,363 Posts
TV sets in close proximity to each other can cause RFI (radio frequency interferrence) from the sweep oscillator circuits and the high voltage power supply. These sets radiate a bit of RF that will beat with another TV set. A computer CPU will also generate this type of interferrence depending on the frequency it works at. Solution is to use shielding on the TV set which is usually impractical to do or move the set farther away from the other oscillator in the system.

Years ago, I used to get called in as a consultant in different low end Video production edit suites to fix this problem. Back then many of these were using consumer grade (not well shielded) TV monitors. Adding Aluminum flat sheets over the cases helped but relocating them farther apart was the answer. Today with more digital monitors in use this is not so much a problem.
 

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Charter Gold Club Member
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22,056 Posts
Cholly said:
...The diagonal lines sound like retrace lines to me.
I haven't seen those in a long time, Cholly, but as you suggest, on a CRT-based tv, it could be visible
retrace lines caused by a low blanking pulse voltage, typically from a failing flyback xfmr, the lines of
which are usually more visible on a dark or blank screen. If the diagonal lines are thin, smooth and
spaced about 1"-2" apart, that could be it. The visible manifestation of the problem can usually
be reduced by adjusting the brightness control.

Otherwise, as Don suggests, it's more likely spurious RFI from a nearby source, particularly if the
lines are uneven or jagged. Make sure your a/c ground is good and all your a/v connections are in
good repair with no breaks in insulation, dielectric or shielding. If that's not it, if practical, reposition
or separate your devices one or two at a time until you can identify the likely source.

Good luck, and be sure to let us know what works for you.
 

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Hall Of Fame
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Retrace lines are visible with brightness all the way up and have a distinctive look. They are well defined and thin. higher on the right than the left. Very stable.

RFI beat freq lines are more shadowey broad diagonal black to gray thick fuzzy lines that also move a bit as the set is moved in position.

Determine which it is and proceed to resolve the defect.
 

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Old Guys Rule!
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I defer to Don and Nick on this one. Retrace lines were the first thing that came to my mind. It's been a loong time since I was professionaly involved with TV, and RFI never entered my mind when I made my post.:slowgrin:
 

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Godfather
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495 Posts
Discussion Starter · #9 ·
The lines are definitely not an inch apart. They are more about 3-4 millimeters in thickness, and about the same spacing. Based on the info above, I'm thinking it might be RFI, so I'll move the CPU away from the TV to test. Good thing I have an extra 25' RCA cable. Thanks. I'll keep you guys posted.
 
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