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Thread: Terrible feedback, can't even hear audio...please help.

  1. #1
    Low Bitrate vwgtipowr's Avatar
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    Terrible feedback, can't even hear audio...please help.

    I'm not sure which forum to post this in, so hopefully someone here can help.

    Today was the first time I actually tried to run the pc in the car.
    here are the basic specs.
    Power supply - m2-atx
    Proc - P3 500mhz
    mem - 256MB
    HD - 40 gig 2.5"
    CD - slim CDROM

    I have a TM-868 touch screen monitor, that is also being driven from the 12v rail. My USB hub is NOT connected yet to the PC.

    The problem I have is everything seems to work great, except for the fact that the audio is so quiet it is barely audible, and on top of it, there is a hissing/gurgling that is so lound on top of it, that it makes it useless.

    I ran all the power wires down the left hand side of the car, and ran the signal wires down the center of the car to the center console. Power wire comes directly from battery, and the ground is ground to an existing ground in the trunk. I used to the dremel to make sure the ground was VERY clean, and ground away at it for a while!

    The weird part is that the feedback I am getting seems to go with the changes in the display, or how hard the processor is working. The display also gets a flicker once in a while also.

    THe TM-868 gets all signal, power and USB input through the single VGA connector. I had to use a 10' VGA extention from best buy to reach the front of the car from the trunk.

    The Audio, is a headphone jack, that is split into left/right RCA cables. The RCA cables are also 10' extension that runs from the headphone jack on the PC (audio out) to the back of my head unit in the dash.

    I have tried to be as descriptive as possible, hopefully someone has some helpfull suggestions, that can point me in the correct direction. I want to avoid having to rip the whole car appart again and rewire if possible.

    I did make the mistake of not testing the audio in the house with the adapter and 10' rca wires. However I did use a 25' headphone extension wire when it was on AC power and it was fine. PC was tested with all other long wires.

    Should the M2-Atx be ground to the battery? Does it matter? Should I ground the metal PC case to the vehicle?

    TIA.
    Car-PC progress meter (researching and collecting hardware)
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  2. #2
    Low Bitrate vwgtipowr's Avatar
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    Unhappy

    Anyone have any ideas?

    Do people usually ground the pc case to the chassis?
    Car-PC progress meter (researching and collecting hardware)
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  3. #3
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    yes ground the PC case to the chassis ground.

  4. #4
    Low Bitrate vwgtipowr's Avatar
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    Quote Originally Posted by junglisitc View Post
    yes ground the PC case to the chassis ground.
    Thanks I will try that first. I might try re-routing the audio signal wire away from the monitor wire too.

    Is it bad practice to ground the PC-case to the power supply ground?

    THanks
    Car-PC progress meter (researching and collecting hardware)
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  5. #5
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    You can never have to many grounds. PC case to PS is good as well. In a conventional PC case, everything grounds through the case to the powersupply.

  6. #6
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    and dont attach a ground to an existing grounding point. that also creates ground loops. reground that and ground your pc case and youll be set
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  7. #7
    Low Bitrate vwgtipowr's Avatar
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    Quote Originally Posted by junglisitc View Post
    You can never have to many grounds. PC case to PS is good as well. In a conventional PC case, everything grounds through the case to the powersupply.
    I am using a conventional case (mounted in the trunk).
    I must just not have enough grounds? Or that is where I will start at least.
    I will create a couple more grounds tonight and ground the case to the otherside of the trunk, and then also ground the case to the same ground as the power supply.

    I get the same feedback whether I just touch the headphone plug to the case, or plug it into the case. Only difference is when it is plugged in there is faint audio in the background of all the feedback noise.

    After all the planning and working on this thing, what a kick in the ***, when the big day came. I was playing an episode of entourage, and I could hear was crackling and hissing, no good.
    Especially when the main reason is to play MP3s.
    Car-PC progress meter (researching and collecting hardware)
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  8. #8
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    junglisitc: yes, you can have too many grounds. For the same reason that sciontC is not correct in his statement.

    You always want to try and attach to an existing grounding point when possible.

    It makes things much easier.

    Grounding to multiple points leaves you open to ground loops.

    I think you have it backwards sciontC

    to the OP - perhaps I just missed it, but can you describe your audio set-up? Your equipment and your method of getting sound to the speakers from the computer?

    also, I'd read here for some good information: Induced noise/Ground loop trouble shooting guide.
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  9. #9
    Low Bitrate vwgtipowr's Avatar
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    Quote Originally Posted by sciontC View Post
    and dont attach a ground to an existing grounding point. that also creates ground loops. reground that and ground your pc case and youll be set
    Ground loops?
    Maybe that is part of my issue too then.

    I have the power supply grounded to a ground point in the trunk, and there is a little ground already attached to it. It is a ground for the trunk light (which is blown btw).

    So you suggest that I drill new holes, clean to bare metal, and ground to that?

    Thanks guys I really appreaciate this.
    I was so ****ed, nice to have people to help me work through this, and keep me sane!
    Car-PC progress meter (researching and collecting hardware)
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  10. #10
    Low Bitrate vwgtipowr's Avatar
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    Quote Originally Posted by RedGTiVR6 View Post
    junglisitc: yes, you can have too many grounds. For the same reason that sciontC is not correct in his statement.

    You always want to try and attach to an existing grounding point when possible.

    It makes things much easier.

    Grounding to multiple points leaves you open to ground loops.

    I think you have it backwards sciontC

    to the OP - perhaps I just missed it, but can you describe your audio set-up? Your equipment and your method of getting sound to the speakers from the computer?

    also, I'd read here for some good information: Induced noise/Ground loop trouble shooting guide.
    I have a headunit that feeds the speakers in the car.
    The headunit has AUX in (left/right RCA plugs).
    The PC has audio out which is just the stereo type headphone jack plug.
    I have a adapter from radio shack that plugs into the stereo headphone type jack and converts the signal to 2 RCA plug. I then have a 10' RCA wire that runs to the headunit and plugs into AUX input.

    Currently I have one ground, and that is just the - PS wire. Case is not grounded.
    Car-PC progress meter (researching and collecting hardware)
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