Could this be gound loop? (1 Viewer)

[adrian.M]

I posted this on the 4805 but since it is more a technical electronic thing i think of posting this here... i don`t know if this is the correct forum though...

I think i`m having ground loop but i`m not sure, i searched and readed everything i found on the internet but i didn`t find anyone on this situation...

From what i read ground loop should happen all the time, if u have the problem of course... on my case it happen only on HD modes... 720P and 1080I to be exact.

Sometimes it does sometimes it don`t...on 480P/I never ever happen, on 720p it does often... and on 1080 it happen almost everytime.

My only source to tried the HD mode is the xbox, i know this isn`t the best way but i don`t have any other source to check Higher modes. The xbox could be defective also or even the MS HD pack could... another posibilty.

The weird thing is that it doesn`t do it always... i`ll try to explain...

When i get this "ground loop" (to give the problem a name) I make it go away by switching back and forth from one to another signal until the lines disapear.
I turn on the projector... i turn on the xbox... it start on 480P... (i have a mod xbox so i have XBMC as Dash) when i switch to 720P it could do the scrolling lines or not... if it does, then i switch back and then go up again to 720p, same thing with 1080. Another "weird" thing is..if the image start up with this lines they never go away as the same as if it starts clean they never show until of course i switch signals.

this "ground loop" only start/disapear when i switch signals...

The descripition are "black/transparent scrolling lines from bottom to top (sometimes from top to bottom).

Now my "technial information".

I read this could be cause by having more than 1 ground... on my case i have none (yeah i know it`s really unsafe, i`m working on fixing this) but... could this ground loop could be caused by having none Ground at all?

Right now on my room i have, the projector 4805, 5.1 Audio Z-680, DVD player, Xbox, TV and PC with, of course, monitor and Wireless Mouse/Keyboard.

I tried disconnecting all this decive and leaving the xbox and Projector and still have this "ground loop" problem.

Could this be ground loop? what is the easier way to check if it is? i don`t want to buy expensive isolators, or something if i`m not suire if is Ground loop.

Also i want to be sure my projector is not defective...

Thanks and sorry for the long post, i`m really scared about this.

 

[John Whittle]

A ground loop usually shows as a rolling line normally of AC (60 hz) frequency rolling thru the picture.

What's your input to the projector?

If you only get it on certain modes, it could be an upscaling problem in either the source or the projector or a problem in the methods used between the two.

Similar problem occur with equipment when you try progressive scan from a DVD player and often the projector does a better job of creating a progressive scan display than the dvd player.

It doesn't sound like you have a ground loop problem although that might be it. Cables that are poor shielding can also be a cause of ground loops along with faulty connectors, soldering, etc.

Find another source with a known good output at the rate you want to test and see what that produces. I would suspect the X box since it's producing all it's own video signals and timing is critical as you go up in resolution. Also is the X box starting with the high resolution and down converting to give you 480i or other formats that are not displaying the problem.

A classic example of why you need to check with good test signals, unfortunately equipment that produces these signals still costs in the thousands of dollars.

John

 

[adrian.M]

Find another source with a known good output at the rate you want to test and see what that produces. I would suspect the X box since it's producing all it's own video signals and timing is critical as you go up in resolution.

I think you are correct about this statement, it seems like an xbox problem

unfortunly i don´t have any other source to produce 720P.. and i don´t have DVI -> DVI Cable... only VGA to DVI.

i tried anyways and it work perfectly on 1024x768 and 800x600.. but still not 720P.