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Author Topic: hum bar in picture  (Read 3267 times)

David Haulman

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hum bar in picture
« on: April 16, 2014, 06:44:05 pm »

I have had this dumped in my lap. Can anybody give me any ideas on this. Video has bar in it. I traced it to the cross they have on the pulpit. It"s rear lighted with bulbs on a Lutron dimmer. When the dimmer is off;picture looks good. as the levels change on the dimmer;the bar gets  stronger or weaker. The way the guy feeds video to projector is; he takes DVI output from computer and splits it. one feed to local monitor and the other thru a 150 foot VGA cable. I wondered if I could run cat5E/6 from the computer thru baluns and into projector composit video input. Any thoughts? Thanks
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Lee Douglas

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Re: hum bar in picture
« Reply #1 on: April 16, 2014, 07:22:16 pm »

The way the guy feeds video to projector is; he takes DVI output from computer and splits it. one feed to local monitor and the other thru a 150 foot VGA cable.

Is it split at the DVI, as in two video outputs from the DVI or is it split at the VGA coming from the DVI, as in 1xDVI into 2xVGA?  If it's the later is it an active or a passive split?
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Scott Hofmann

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Re: hum bar in picture
« Reply #2 on: April 17, 2014, 10:43:31 am »

Assuming incandescent bulbs, replacing the dimmer with a higher quality unit having more filtering will probably fix the problem.
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Scott Hofmann

David Haulman

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Re: hum bar in picture
« Reply #3 on: April 19, 2014, 01:34:28 pm »

I have had this dumped in my lap. Can anybody give me any ideas on this. Video has bar in it. I traced it to the cross they have on the pulpit. It"s rear lighted with bulbs on a Lutron dimmer. When the dimmer is off;picture looks good. as the levels change on the dimmer;the bar gets  stronger or weaker. The way the guy feeds video to projector is; he takes DVI output from computer and splits it. one feed to local monitor and the other thru a 150 foot VGA cable. I wondered if I could run cat5E/6 from the computer thru baluns and into projector composit video input. Any thoughts? Thanks

Dimmer looks new. Doubt they would replace it. The video split is at the computer itself. Looks like a passive Y-split. One to local monitor other to the projector. Power feed is probably differnt legs of power. But I haven"t got that deep into it. Still  wondering if the cat5/6 with baluns would help?
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Rob Duncan

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Re: hum bar in picture
« Reply #4 on: April 19, 2014, 02:45:21 pm »

Power feed is probably differnt legs of power. But I haven"t got that deep into it. Still  wondering if the cat5/6 with baluns would help?

When you are seeing hum, unplug the line running to the pulpit. Does the problem go away? If so, electrical isolation of that long run will likely eliminate the problem (on your main screen at least).
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Kevin Graf

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Re: hum bar in picture
« Reply #5 on: April 20, 2014, 09:41:01 am »

These two Bill Whitlock seminar papers have sections on troubleshooting and video:

2012
"An Overview of Audio System Grounding and Interfacing"
by
Bill Whitlock, President
Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society
Life Senior Member, Institute of Electrical & Electronic Engineers
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

2005
Generic Seminar Template
Instructor
Bill Whitlock
president
Jensen Transformers, Inc.
Chatsworth, CA
http://www.jensen-transformers.com/an/generic%20seminar.pdf
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Keith Broughton

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Re: hum bar in picture
« Reply #6 on: April 21, 2014, 08:36:06 am »

These two Bill Whitlock seminar papers have sections on troubleshooting and video:


Thanks for posting.
Just re-read the first one and it's a good refresher for even experienced trouble shooters  :)
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Miguel Angel Castro Rios

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Re: hum bar in picture
« Reply #7 on: June 19, 2014, 06:42:03 pm »

I have had this dumped in my lap. Can anybody give me any ideas on this. Video has bar in it. I traced it to the cross they have on the pulpit. It"s rear lighted with bulbs on a Lutron dimmer. When the dimmer is off;picture looks good. as the levels change on the dimmer;the bar gets  stronger or weaker. The way the guy feeds video to projector is; he takes DVI output from computer and splits it. one feed to local monitor and the other thru a 150 foot VGA cable. I wondered if I could run cat5E/6 from the computer thru baluns and into projector composit video input. Any thoughts? Thanks

Sounds like a ground loop.
Make sure your AV gear is well grounded, and have it come from the same power source (distro)
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Thomas Lamb

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Re: hum bar in picture
« Reply #8 on: July 01, 2014, 12:50:37 pm »

Dimmer looks new. Doubt they would replace it. The video split is at the computer itself. Looks like a passive Y-split. One to local monitor other to the projector. Power feed is probably differnt legs of power. But I haven"t got that deep into it. Still  wondering if the cat5/6 with baluns would help?

So they want to keep the bars in the picture.... The problem is the problem. What fixes it fixes it. Changing video equipment because you have a crappy dimmer is no beuno.
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bigTlamb

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Scott Hofmann

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Re: hum bar in picture
« Reply #9 on: July 02, 2014, 12:43:06 am »

Dimmer looks new. Doubt they would replace it. The video split is at the computer itself. Looks like a passive Y-split. One to local monitor other to the projector. Power feed is probably differnt legs of power. But I haven"t got that deep into it. Still  wondering if the cat5/6 with baluns would help?

I guess I should have stated my previous comment another way:
a cheap dimmer that looks new is still a cheap dimmer, which is the cause of your problem. Just trying to be helpful.
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Scott Hofmann

ProSoundWeb Community

Re: hum bar in picture
« Reply #9 on: July 02, 2014, 12:43:06 am »


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