Help with video interference -> s-video cable

[Dustin Mustangs]

I am getting some video interference with my setup that has been driving me crazy.  My rig is a dell dimension with the dell supplied tv out graphics card hooked up to a standard 27inch tv with a svid cable.  I had this all setup before the cab was built and the picture looked great (imo).  When I loaded everything into the cab I started getting this horizontal band (most visible on black backgrounds) that slowly moves vertically across the screen. 

I double checked that all my power cables and video cables were no closer to each other then needed, no help there.  Tried a new svid cable, even worse.  I started unplugging things like the marquee light to see if they were causing it, no luck.  Finally, I brought another tv over, set it next to the cab, plugged it into the same power strip and used the same svid cable.  Picture looked great.

Does this mean it's my tv that's causing this?  Or is this more likely interference from something else around it??  How would I go about trouble shooting this further???  It just seems weird that I had no problems until it went (smoothly) into the cab.

Out of ideas and looking for some help....

 

[grantspain]

could be down to the earth,perhaps the s-vid is picking up rf interference
maybe a shielded cable would help

[Dustin Mustangs]

Care to expand?  Aren't most svid cables shielded nowadays or is that something special??  And what do you mean by down to earth???  I'm a lil slow...

[grantspain]

its down to some kind of earthing problem,either the tv is not earthed or your cab has no earth.
seen this problem from time to time and its always  earth related

i don't think all svid cables are shielded

[Dustin Mustangs]

Well, I ran the circut my cab is pluged into and it is grounded (earthed) correctly.  The power strip everything's plugged into has the grounded 3 tong plugs, but the tv's plug only has two meaning it isn't grounded.  Is there a way I can ground the tv or what else would you suggest I try grounding?

Thanks for the input...

[Todd H]

What brand of s-video cable is it? Have you installed any new appliances recently?

[Dustin Mustangs]

The cable I am currently using is an Acoustic Research brand.  Not the best, but I have tried other, more expensive ones, and gotten worse results. 

No new appliances.  Like I said, the problem started when I loaded all the electrics into my cab and fired it up for the first time.  I had it set up on a counter before that and it worked fine.  The only thing that was really added at that time was the marque light and the extension cord that powers it off the power strip. 

[TOK]

If the bar is moving bottom to top then starting over, it sounds like a 60 cycle hum and Greatspain is on the right track. In very basic terms it means that there is some trace AC getting into your video circuit. As a test, you could try running a ground lead between the computer power supply and the regular antenna in (ANT) of your television... Just touch it to the outside of the barrel.
Linking all your grounds to a common point is usually the solution to a problem like this, though the source can be maddening to find.

[richms]

If its a solid looking bar its often getting noise from a light dimmer.

Post pics if you can.

[Dustin Mustangs]

If the bar is moving bottom to top then starting over, it sounds like a 60 cycle hum and Greatspain is on the right track. In very basic terms it means that there is some trace AC getting into your video circuit. As a test, you could try running a ground lead between the computer power supply and the regular antenna in (ANT) of your television... Just touch it to the outside of the barrel.
Linking all your grounds to a common point is usually the solution to a problem like this, though the source can be maddening to find.

This did clear up about 95% of what I was seeing so I am a happy camper now.  All I did was link a ground from the power supply to the coax barrel as you suggested.  I set it up so I can leave it like this but you make it sound like there is a better way and that this was a test just to see if that was the problem.  Now that I know this is my issue, is there indeed a better way to handle it?  Maybe related, how would I link all my grounds to a common point and what all would need to be linked in a typical mame cab??

Thanks for the help!

 

[TOK]

If you're happy with that as a solution, it won't hurt anything to leave it. I put a ground lug in all my cabinets and try to get each component back to it. If you have the power supply, TV, encoder and some part of the the physical panel (via joystick/trackball mounting bolts) on a common ground, you probably wouldn't see hum unless a component in the power supply or TV is failing and it also prevents static shocks from the panel in the winter.

The lug I use is just a metal block with a 7/16" bolt in it that clamps onto all the grounds. The leads to it don't need to be anything fancy, standard control panel wire is fine.