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Could this be gound loop?

Discussion in 'Projectors, Screens & Video Processors' started by booker, Jul 21, 2005.

  1. booker

    booker
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    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).

    I`m posting a Custom screen (i made it on photoshop to give you an idea, it`s not real) to explainmyself.

    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.
     

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  2. cyberheater

    cyberheater
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    First thing.

    * RECONNECT YOUR GROUND LOOPS!!!!!
    For fudge sake. People die every year from this...

    * If it's not happening on lower resolutions then I guess it could be a faulty PJ.
    The 4805 isn't a hi-rez PJ anyway (only native 480P I think) so what is the problem with only displaying that format.

    Is it still under warranty. If so, get it back to them and explain the problem to 'em.

    If possible. Can you take it round a mates house and try it on his hi-def equipment to confirm it's not your stuff.
    Maybe take your DVD player round with your PJ. That will confirm if its a ground loop issue.

    Last thing. Does it do it on PC.
     
  3. terrysharp

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    It can't possibly be a ground loop problem because you say yourself, that you have no ground connected at all.

    Ground loop problems accure when you have two seperate devices both connected to ground.
     
  4. binbag

    binbag
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    Until you have tried another 720/1080 source you can't discount the source as the problem. It may be the onboard scaler can't always resolve the signal it gets from the x-box. I had similar lines across the display when I had the vertical resolution out on my custom setup from my dvd - although they didn't scroll.

    I'd also look at swapping the signal cable or moving it if it's a long run (not DVI is it?) alongside a power source. In any case if the x-box puts out a 480 signal then I'd run that anyway as thats 2 less conversions between disc and screen.
     
  5. ZippyCat

    ZippyCat
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    If you are experiencing ground loops problems you must have one big house! Ground loops will occur when two devices are connected to grounds of different potentials. It is highly unlikely to be the case in a domestic dwelling due to the small scale of the electrical distribution system. All earth connections will radiate from a central earth bar, not multiple bars located in different parts of a large building. Ground loops are very common in CCTV systems where cameras can be located large distances from control equipment and monitors.
     
  6. booker

    booker
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    ok, i was doing some search and testing.. this is what i did..
    i don´t think is a ground loop , since like you guys mention i don´t have ground :)
    I´m working on it to reconnect the ground... :)

    After doing some research i´m almost certain the problem is on the xbox who is not "proccesing the singal" correctly on HD format.

    I did try my PC by M1 (DVI) and it worked on 1024x768 and 800x600 perfectly.
    I also have the DVD player wich have no issues at all on lower resolution.

    Since the signal is comming fro the xbox, and it´s already on progresive i believe the xbox is not proccesing the singal well, it seems like a sync issue.

    Also if it were the projector it should happen everytime, and remember if i switch back and forth, the problen can go away.. once the signal is displayed, then it won´t change at all.

    Sounds like a defective xbox, doesn´t it, it seems the xbox is not processign (deinterlacing the signal correctly, this is why i need to re "refresh" (by chaning from signal to signal) the signal.
    what do you think?

    What i can do to make sure the PJ is working ok?... there are any other way?
    I can connect my PC but only by VGA ->DVI
    don´g have DVI to DVI.
     
  7. booker

    booker
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    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. (from other member of other forum)

    This is what i tried to explain on my last post, sound reasonable...ideas?
     
  8. biglyle

    biglyle
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    A gound loop is usually a single (whitish) line that will scroll from the bottom to the top of the screen over and over, hence the term loop.
     
  9. booker

    booker
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    well even i do know ground loop is not what i have, my lines are like that.. scrolling from bottom to top...

    from what i read the lines could change from display to display.
     

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