VGA cable filter

Posted on 2010-04-09
Medium Priority
Last Modified: 2013-12-11
I have a laptop (quite old) plugged into a new 19" lcd screen via a vga cable. There are scrolling lines on the lcd screen that are apparent when the laptops power supply is plugged in but not when its running on batteries so I am guessing that these lines are being caused by a 'dirty' power supply interfering with the screen. Is there some kind of filter I can put on the vga cable to reduce this problem or is there any other solution anyone has come across?
Thanks in advance...

Question by:activateahsd
LVL 12

Expert Comment

by:Craig Bowman
ID: 30200536
It sounds like a ground loop issue.  Do you have access to a plug adapter like this?

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Expert Comment

by:Craig Bowman
ID: 30202925
Another way you could try this would be to try to cover the ground point on your ac adapter (with thin electrical tape or something similar) and plug it in the wall.  Given that the electrical tape doesn't tear and keeps the plug from getting that ground connection... then you should get the same result if the plug above.  

Author Comment

ID: 30203155
Hi - thanks for the info - that plug adapter you show the picture for, can you tell me what its called so I can do a search for it?

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Expert Comment

by:Wes Miller
ID: 30203641
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Expert Comment

by:Wes Miller
ID: 30204797
As an additonal explanation of what you are experincing see:
It is called:  Electromagnetic interference, EMI, is any undesirable electromagnetic emission or any electrical or electronic disturbance, man-made or natural, which causes an undesirable response, malfunctioning or degradation in the performance of electrical equipment.
So although what has been suggested may work a better fix would be to add an EMI Filter.
See: X10 Pro Plug-in Filter Module XPPF , If above method doesn't work then this should,
Avalaible at Amazon for $19.90 : http://www.amazon.com/X10-Plug-Filter-Module-XPPF/dp/B0002M5OJI
LVL 70

Accepted Solution

Gary Case earned 2000 total points
ID: 30224309
Whoa !! The last thing you want to do is eliminate the ground connection!!

Do NOT "... cover the ground point on your ac adapter (with thin electrical tape ..."

... and a 3-prong adapter does NOT provide a ground => it's in fact designed to let you plug a grounded plug into an outlet that doesn't provide a ground.

Neither of the above are good ideas ... and neither is likely to make any difference.

What you most likely need is simply a better quality VGA cable. Are you using a cable with ferrites? [See this picture ... the round cylinders at each end of the cable are ferrites (electronic filters that eliminate "noise" on the signal lines): http://www.monoprice.com/products/product.asp?c_id=102&cp_id=10201&cs_id=1020102&p_id=85&seq=1&format=1#largeimage]  .

Chances are excellent that all you need is a good cable with ferrites and your problem will disappear. This would be a good choice: http://www.monoprice.com/products/product.asp?c_id=102&cp_id=10201&cs_id=1020102&p_id=85&seq=1&format=2

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