Lighting Power vs Video Hum - Isolation

[tohmit]

Hello,

Hopefully someone here might be able to help. I have gotten some conflicting answers from companies.

Our church has a theatrical lighting system run on all 3 phases, 100A ea. We have 3 Leprecon dimmers. Each dimmer uses all 3 phases of power.

We recently did a large lighting upgrade. We added the third dimmer (same model) and some Par 64's.

Now we are getting video feedback on our projectors in the form of scrolling lines going up the screen. This occurs when we run the Par 64's at less than 100%. When they are at 0% or 100% there is no problem. If they are on 50%, there's a problem. The problem is also gradually worst with the more lights that are on 50%.

Unfortunately, the system is hard patched with all of the Par64's on the new dimmer. My first question is, could this be a defect with the new dimmer? Or is this common with Par64's?

I called the lighting dealer that we worked with for the upgrade, and they think we need an isolation transformer to isolate the lighting system from the rest of the building.

I called a company that sells isolation transformers, and they told me that will not solve our problem.

Does anyone have any suggestions? I am not sure how to move forward in troubleshooting and solving this problem from here.

Thanks,

Tom

[CCCLights]

Hi Tom, we had this problem also with aour lighting and video being on the same transformer. This product from Extron http://www.extron.com/product/produc...000&subtype=45 fixed our ground loop. The one we used was for RGBHV, not sure what signal you are running. But I do know one thing, you will have to break out the big check book for this. IIRC approx $1200 ea. We had to buy two!
hope this helps,
--Chuck--

[tohmit]

Thanks Chuck. Looks like we may need one of those. I'm still trying to troubleshoot. Maybe I can figure something out and save some bucks.

I have figured out that the video hum only appears on the RGB sources (Mac or PC). It does not appear when I switch to DVD player, camera, etc. All of my inputs are run through an Extron scaler. Then, we run RGB 15-pin to the projectors. I found that interesting that it only appears on the RGB sources.

Any other ideas anyone? I don't mind some soldering work if it will save some money.

[Johnnycat]

Try putting just the computer on an iso transformer...

http://www.partsexpress.com/pe/showd...number=125-130

[prochlea]

Jensen transformers has an RGBHV transformer for $800ish... If you can talk someone into letting you return it if it doesn't work - that would be the way to go. Jensen might let you - they're a fairly small company that has really good stuff for ground loops.

I think this is what you're going to need, but if you had to pay a restocking fee, that would probably be cheaper than some of the other options. it's a place to start anyway...

Oooh - I just had an idea- hook up a laptop, but don't plug it into the power. See if you get hum bars then. If you don't get the hum bars - a video transformer should do the trick.

[tohmit]

Thanks for the product ideas everyone!

Pat, that is a good idea, thanks! If that works, I can plug the laptop straight into the projector first, then add things into the line gradually to see what piece of gear is actually causing the hum.

[tohmit]

Well, I tried a couple things. One was to run the laptop straight to the projector, run off of battery power. It looked much better, but there was still a hint of video hum. It was slightly different though. The lines kinda flickered as they scrolled.

You guys still think an iso transformer would do the trick?

I also tried going directly out of my Mac Pro to the projector, bypassing all of our extron scalers, DA's, etc... It still had video hum as well.

The odd thing I have found is that if I run a video source through my Extron scaler (such as a DVD player), I do not get the video hum. Even though I am still outputing RGB to all the projectors from the scaler.

[prochlea]

at this point it's seeming like the dimmer packs are putting out some electrical inference that is high frequency enough to affect the RGB signals but stay out of the way of a composite video source. You probably need some power isolation between the video system and the lighting. it would probably be cheaper to put power conditioners on the video stuff rather than the lighting - but you would need it on everything - computer, projectors, scaler, etc...

[Donald V]

We have all of our video & audio on two isolated electrical panels. All the audio is on a sequenced lyntec panel that turns on the audio in order. Then we have the rest on the other panel. It has solved all the problems from dirty electrical sources... ie. Lighting, A/C, microwaves, etc...

While it will be really expensive to run new electric panels you might be able to put isolated transformers on the video system to eliminate the problem.

Donald

[tohmit]

How I wish I had dedicated electrical panels to each AV system! That would be nice.

I have run some more tests. The only thing I can do to eliminate the video hum is to put a ground lift adapter on the projectors. I do not want to run my projectors without a ground...call me old fashioned....so I am looking at the iso transformers. Thanks for the help everyone!

[prochlea]

old fashioned - not at all... those ground lift adapters are dangerous... potentially deadly.

[D.R.HADDOCK]

I had a simular problem,I came to the conclusion that It was radiation from the lighting system, If you just had an upgrade and installed some par 64s,these are a heavy load and when a heavy load is rapidly switched (dimmed) these is bound to be some radiation, the larger the load the worse it gets, in my case it was the house lighting, which was a large load of 42a, we solved the problem by using better quality equipment, paying attention to grounding ( make sure everything in grounded, dont use unearthed double insulated equipment ). also if possable sheild as much of the lighting cables as possable, in our case we shifted the wiring looms so they run inside the metal roof beams and trusses, the metal beams are a good sheild. you could try sheilding the RGB cables better. DONT USE ANY METHOD OF GROUND LIFTING as this opens you up to potentail legal litigation.