Projector Issue - with horizontal lines

[mshill]

Hi

 

We have a projector in the school hall that when connected to a PC or Laptop with a powered source gives horizontal lines scrolling up the screen. If we connect a non powered laptop this pretty much vanishes.

 

We have had electricians and AV specialists in and none of them have been able to solve this problem. I have read lots about Ground loops, would a ground loop isolator solve this problem? might it be another device on the same power circuit causing the issue? or does anybody have any other ideas for tests and fixes?

 

We also have a composite connection running from the same projector to a freeview box, this works fine without any issues on horizonal lines.

 

Thanks

[steveg]

IT can be caused by an earthing issue on the circuit. Have you tried running an extension cable from the other side of the building and powering the laptop off this? Does it then go away?

 

We had this with a bunch of Acer laptops, cheapest way to solve it in the end was to put desktop pc's into the few classrooms that were affected - cheaper than a rewire, just used the laptops elsewhere.

 

Steve

[Oaktech]

see here... http://www.edugeek.net/forums/av-multimedia-related/84017-crackling-sound-system.html

 

chances are what you are seeing is a visual representation of the sounds in this post.

 

Ultimately the solution is to either wire the VGA shielding to earth, or to unwire it if it is already.

 

You may find the groundloop is occuring because the psu and projector are not on the same supply. when i specify an install i always spec a double socket on the same supply as the projector to deal with this issue.

[mshill]

Unfortunately I have no idea how to do that lol. How can you tell if the shielding is wired in or not? and is this to be done where the vga cable comes into the box connected at the wall?

 

It might be worth saying the cable looks like it could be over 25m could this be an issue?

[mshill]

Would this solve the problem?

 

Atlona Technologies connectivity solutions, cables, splitters, extenders, distribution amplifiers, converters, switchers for commercial, professional and industrial applications

[Marc-Engineer]

If you have a lead i recomend you try a different VGA lead from a laptop to the back of the projector it sounds like a broken lead if the Sync wire is broken or damaged screen (no there is no way of checking without stripping the insulation off) it can upset the imageyou will get rolling lines taking about 2 seconds to cover top to bottom and usually scrolling down.

Try different lead let me know.

 

Marc

Projector Engineer

[StaffordCabling]

One more thing to try is to run the VGA through a splitter, as the built in amp sometimes helps with this and I'm sure you have one around to try as a test. We have some sites where this is an issue even when both are plugged into the same socket. Usually a different lead can sort it but if it's 25m long that could be a pain. Try the laptop plugged in via a small 2m lead and see if it does the same thing. One last suggestion if all else fails is to see if you can swap the projector for one in another room, as some models are worse than others for this.

[Hulbert99]

Could try a ferite ring on the power lead?

 

We had it in a few of our schools with a batch of Acers that obviously had cheaply made power adaptors. In the end the cheapest (free) way to get round it was to have your laptop unplugged when presenting on the board! Not much use if its happened when connected to a PC but a workaround for laptops!

[Marc-Engineer]

On the acers its the earth lead that causes the problem, if you use a 2 wire PSU it doesnt have that problem (normaly its the other way around).

 

Marc

projector Engineer