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Author Topic: lines in video projection  (Read 2116 times)

Bill Beach

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lines in video projection
« on: October 02, 2014, 11:56:54 am »

we recently changed from 1 central projector to 2 projectors on left and right of stage.  using the same VGA signal and cable (about 110 feet from splitter/extender) and added a Kramer VP-200K 1:2 splitter then 25 feet to the new projector positions.
we now have a faint horizontal line on each projector that moves quite slowly across screen; sometimes from top to bottom and vice versa.
I know there will likely be questions about equipment that I will need to look at the equipment to know the right identity, but, for me, if I don't get this started now who knows when it might happen?
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Stephen Swaffer

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Re: lines in video projection
« Reply #1 on: October 02, 2014, 03:03:26 pm »

Almost certainly a ground loop somewhere.  Where are the new projectors powered from in relation to the old one?

Try one projector at a time leaving out the Kramer to see if the problem is still there.
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Steve Swaffer

Bill Beach

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Re: lines in video projection
« Reply #2 on: October 05, 2014, 10:07:48 pm »


Where are the new projectors powered from in relation to the old one?

different conduit to the front but powered from the same main on/off switch
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Stephen Swaffer

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Re: lines in video projection
« Reply #3 on: October 08, 2014, 01:38:29 pm »

So a different conduit implies a different ground and or neutral feeding the receptacles.  There have been several discussions on here-and on the AC Power and grounding board-might do a search on "ground loops" for ways to track down the issue.  Mike Sokol in particular has much more experience tracking these down than I do.
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Steve Swaffer

Bill Beach

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Re: lines in video projection
« Reply #4 on: October 11, 2014, 10:24:55 pm »

So a different conduit implies a different ground and or neutral feeding the receptacles. 
I hooked up one of the new projectors to the power that supplied the one central projector (I don't remember, but they tell me there wasn't a line with the old setup) -  still had the line.  interestingly, (at least to me) while powering one projector from the previous power source, also had the other one still running off the newer power source and the line still moved identically in the 2 different projectors.
bypassed the Kramer VP-200K and sent signal to one of the projectors - still had the line.
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Lee Buckalew

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Re: lines in video projection
« Reply #5 on: October 11, 2014, 10:41:39 pm »

I hooked up one of the new projectors to the power that supplied the one central projector (I don't remember, but they tell me there wasn't a line with the old setup) -  still had the line.  interestingly, (at least to me) while powering one projector from the previous power source, also had the other one still running off the newer power source and the line still moved identically in the 2 different projectors.
bypassed the Kramer VP-200K and sent signal to one of the projectors - still had the line.

For troubleshooting you can't move only one projector back to the original source.  They are still linked by the video cables.
You need to run only one projector at a time, eliminating even the Kramer from the run. 
If the two projectors run independently of each other and of the Kramer without the ground loop showing then connect only one through the Kramer (be sure you don't connect any runs to the other projector) and see if the Kramer introduces the hum bar.

You will only find the problem by accident or by a systematic process that begins at one end of the other of the system and works it's way through.
Since you did not have this problem before, go back to them configuration and be sure that there is still no ground loop.  Then add the Kramer into only the original run, powered from the original projector power.  If no problem then add the Kramer connection to the new projector but power the new projector from an extension cord coming from the original projector power.  Do not use cheap box store "surge suppressor" plugging strips to do this.  The MOV's in them fail over time and cause problems.  If you are using an older one now that could be the problem or a part of the problem.
If there is no problem then reconnect the new projector to its new power. 

Stepping through things in this manner should let you find the point at which the ground loop on the fault ground is allowed to pass and get into the signal ground.

Lee
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Lee Buckalew
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Bill Beach

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Re: lines in video projection
« Reply #6 on: October 20, 2014, 09:25:12 pm »

I moved the power source back to the original source for the 2 new projectors as well as the Kramer splitter.
Voila!!
no line!!!!!!!!!!!
thanks everyone!!
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ProSoundWeb Community

Re: lines in video projection
« Reply #6 on: October 20, 2014, 09:25:12 pm »


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