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Thread: alternator whine though video composite cable on xenarc 700idt?

  1. #1
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    alternator whine though video composite cable on xenarc 700idt?

    hello there.
    ive just been putting in my car pc today. using a xenarc 700idt as a monitor and an asus eee pc in the glove box. the monitor is in a double din slot, so ive left in my sony head unit.
    but the head unit only has one aux in, so i built an input selector out of an old amp to select between the ipod adapter, tv tuner, pc and the nokia n95 video cable. i have the xenarc showing the tv tuner and nokia n95, but it seems to add alternator whine over the shared ground on the composite cables.
    the whole lot is running of the same loom behind the stereo.
    so what can i do to get rid of the alternator whine?
    any help greatly appreciated.

  2. #2
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    I dont have a answer to your question. But if you could post some pictures of your setup maybe that would give me better idea of the setup.

    Thanks

  3. #3
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    Video signals are more sensitive to noise than audio signals. You said you built and switcher out of an old amp? What amp is this do you have a pic or schematic.

  4. #4
    Variable Bitrate brucedog's Avatar
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    I always got the whine when I powered the monitor using 12 volts dc. No matter where I hooked the 12v+ to, whine was there...

    So, I used an inverter to power the monitor ac/dc adapter, and whine just wasn't there anymore.
    Happy CarPC'ing!

  5. #5
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    You can also use a power filter that gets wired inline with the power wires that would also kill the video noise. on cheap headrest monitors with built in ir emitters for wireless headphones benifeted from that type of filter.

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    I have a similar problem, although I may have a different cause. I have an 8" lcd and touchscreen stripped from a monitor acquired through ebay.

    The screen has always had video whine (horizontal waves travelling down the screen).
    In the past I have had it powered via the acc line, and through a regulator, and filtered with a choke, and now powered direct from my m2atx which i relocated to the front of the car.

    The whine is still there even when powered from the m2atx.

    One possible cause is the cheap vga board that runs the lcd.
    It ties all the 'grounds' in the vga line together to save wiring. ie. shield, red ground, blue ground, green ground etc etc.
    This is not as per the vesa standard i believe.
    Does anyone truly have some expertise with the vga standard?

    The monitor is in the console, and the carpc under the passenger seat with power and vga from the carputer running straight under the center console and forward to the monitor.
    Is there still enough of a ground loop to cause the horizontal lines?
    Is there a cheap way to eliminate video ground loops?

    i personally believe that the wiring of the vga cable/plug on the lcd controller board is the likely culprit as the artefacts on screen sometimes appear to associate themselves with boundaries of high contrast (eg the transition from a bright white album art to the black background of my RR skin)

  7. #7
    Variable Bitrate numbers's Avatar
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    Quote Originally Posted by barbarianbeast View Post
    hello there.
    ive just been putting in my car pc today. using a xenarc 700idt as a monitor and an asus eee pc in the glove box. the monitor is in a double din slot, so ive left in my sony head unit.
    but the head unit only has one aux in, so i built an input selector out of an old amp to select between the ipod adapter, tv tuner, pc and the nokia n95 video cable. i have the xenarc showing the tv tuner and nokia n95, but it seems to add alternator whine over the shared ground on the composite cables.
    the whole lot is running of the same loom behind the stereo.
    so what can i do to get rid of the alternator whine?
    any help greatly appreciated.
    It would be helpful if you could begin unplugging things one by one and determine when the whine stops, then try to plug everything else back in to isolate the one component which causes it.

  8. #8
    Variable Bitrate numbers's Avatar
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    Quote Originally Posted by MunkyWrench View Post
    I have a similar problem, although I may have a different cause. I have an 8" lcd and touchscreen stripped from a monitor acquired through ebay.

    The screen has always had video whine (horizontal waves travelling down the screen).
    In the past I have had it powered via the acc line, and through a regulator, and filtered with a choke, and now powered direct from my m2atx which i relocated to the front of the car.

    The whine is still there even when powered from the m2atx.

    One possible cause is the cheap vga board that runs the lcd.
    It ties all the 'grounds' in the vga line together to save wiring. ie. shield, red ground, blue ground, green ground etc etc.
    This is not as per the vesa standard i believe.
    Does anyone truly have some expertise with the vga standard?

    The monitor is in the console, and the carpc under the passenger seat with power and vga from the carputer running straight under the center console and forward to the monitor.
    Is there still enough of a ground loop to cause the horizontal lines?
    Is there a cheap way to eliminate video ground loops?

    i personally believe that the wiring of the vga cable/plug on the lcd controller board is the likely culprit as the artefacts on screen sometimes appear to associate themselves with boundaries of high contrast (eg the transition from a bright white album art to the black background of my RR skin)
    You are correct - these grounds are all supposed to be separate. However, this does not normally cause problems at lower resolutions and refresh rates. While it certainly isn't helping matters, you should be able to solve your issue by other means. I would recommend that you start by adding grounds to the monitor and pc. Not both at once - just one at a time. First find a good ground connection close to the monitor (a GOOD connection or else don't even bother) and add it to the monitor's power connector. If that does nothing, do the same for the carpc. After that, try adding a ground on one end or the other of the vga cable. Fixing noise issues can either be a complicated science or a free-for-all of trying countless things. Both will lead to the solution, but frequently the latter does so more quickly.

  9. #9
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    Quote Originally Posted by brucedog View Post
    I always got the whine when I powered the monitor using 12 volts dc. No matter where I hooked the 12v+ to, whine was there...

    So, I used an inverter to power the monitor ac/dc adapter, and whine just wasn't there anymore.
    I've been having the same issue with my Xenarc 700tsv. I found this post and gave brucedog's resolution a shot.. I hooked up my Xenarc to my inverter using the ac plug and bam.. Lines gone.

    I plugged it back in to the 12 volt cigarette adapter and the lines were back.

    A good power inverter will provide a true-sine wave which is basically going to provide clean power to a device while anything less supposedly will cause the noise, ie horizontal lines.

    The link below doesn't actually pertain to monitors in particular, but the concepts behind the wave:
    [URL="http://http://autospeed.com/cms/A_109871/article.html"[/URL]

    Basically I'll bet if you hook up an oscilloscope to the output of a power inverter, you'll see a nice, true sine wave coming from it and probably a not-as-nice wave coming from the cigarette lighter.

    But I may be wrong, I really don't know for sure, it just sounds logical to me in theory.

    So for me, I'm going to chop up my ac adapter, splice in some length in there, and run that mug from my inverter up to the Xenarc and it better just be the best.

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