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Weird Sound Problem. Help!

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  • Weird Sound Problem. Help!


    I've got a problem with the sound on my motherboard. I'm using a Biostar M7VIZ MB with AMD 2300 and onboard sound > amplifiers > speakers. I've also got a 400 watt inverter powering the computer.

    I installed everything, hardware/software, inside the house and everything works fine. Sound was working using a standard miniplug to RCA cable. This was connected to a Panasonic Home Amp that I use for everyday movie/tv watching. I am running Roadrunner btw. When I put everything inside the car the sound would not work. No opening windows sound or anything. Checked all settings even though I didnt change anything. Took it back into the house and everything was working fine again. Back to the car again and no sound.

    Now, this is the weird part. I dissconnected the miniplug from the green/headphone jack of the onboard sound and connected the cable to my portable MP3 player. It works! Disconnected the cable and plugged it back into the onboard sound and it stopped working.

    Anybody got any ideas? I haven't changed any wiring whatsoever from my last configuration. All I've done is switch MB and my last MB did not have this problem which also used the onboard sound. Please help, I'm stumped.

  • #2
    it just dosnt like you lol naw jp hmmmm thas kinda weird :-P are u using the same cable inside the house as in the car?? try to swap em maybe it will work


    • #3
      I tried using the house cable in the car but it made no difference. I didnt expect it to since the cable worked fine when I used my portable mp3player.
      Thamks for the suggestion.

      I messed around with it again and discovered that it seems to be a grounding issue. I can hear music when I don't use the shield of the RCA cable going into the amp. It cuts out as soon as I plug the RCA in all the way. I didnt play around with it too much since it's not good for any of the components.

      Does anyone know how to fix this grounding problem? The amps are drawing power directly from the battery and are grounded to the battery. Remote wire is powered by ignition. MB is mounted on a piece of MDF with the Power Supply and hard drive next to it. None of those 3 pieces are touching each other. I thought the ground from the ATX MB power connector was sufficient. Should I ground the MB/Harddrive case/Powersupply Case together?

      What really ****es me off is I'll take this piece of wood with all components inside the house and it works everytime!!! Arghhhhhh!


      • #4
        If I understand this right, you've got an issue where the RCA's work in the house, but not in the car, right? Do this: measure the voltage difference between the ground of the amp's RCA terminals and the ground of the soundcard output on the mobo. My guess is that there's a "floating" ground somewhere, and it's not "true" ground - that would cause the differential between the center conductor of the RCA's to be basically equal to the shield - basically putting you at 0volts, or no sound. When you connect *just* the center terminal on the RCA's (either at the amp or at the source end - doesn't matter), you end up with a situation where the signal isn't pulled to 0v. Am I making any sense? It's not necessarily a "short" per se, but more of a difference in the reference to the car's ground - my guess is that the amp is fine, but the PSU has created its own reference to ground, and that doesn't match what the car is.

        Oh, how to fix it? Hmm. I'm inclined to tell you NOT to ground it to the car - at least not yet. I'd start by measuring a bunch of stuff - mobo to hdd, mobo to psu, mobo to car ground, etc... and see what you come up with. I'm convinced that this is where the problem is, but I'm not about to tell you to ground it and risk frying yer hard-earned $$$ - I'd do it to mine, but I don't have to answer to anyone.
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        • #5

          Did a few measurements and this is what I came up with...

          From +12V on Powersupply to Onboard Sound Ground = 11.85V
          From +12V on Powersupply to Ground of MB = 11.85V
          From +12V on Powersupply to Case of Power Supply = 11.85V
          From +12V on Powersupply to HDD casing = 11.85V

          So it's safe to say that MB, HD, And powersupply are grounded well and there should be no problems between them.

          From +12V on Amp to RCA Shield on Amp = 11.06V (Car was on, not running)
          From +12V on Amp to Onboard Sound Ground = 23.64V (That's weird. Crap, can't remember if I was getting -23.64V)

          So, I switched out a different amp with the same results and then tried a different powersupply and it also made no difference. Once again, took it back inside the house and it works fine!


          • #6
            First, sorry for the delayed response. Second, that 23V is very odd (obviously). What about going from soundcard ground to RCA ground? Or what about from soundcard ground to mobo (or even PSU) ground? I'm thinking that's where the problem lies - the one ground isn't the same as the other ground, and that's where you're getting the signal cancellation. We know the equipment is all good, because it all works when hooked up to other stuff. What we haven't figured out yet is where the ground loop is - that's the challenge that lies ahead.
            To find your favorite restaurants in Houston, check out

            If it's not fun, you're not doing it right!


            • #7
              Thanks alot for all your help! I don't know what I did but everything is working fine. I just got sick and tired troubleshooting and ripped everything out and rewired it again from scratch. Everything checks out. I changed a few things to make wiring a little simpler. It might have been something as simple as changing one ground to a different location. Who knows, I'm just happy it's working. Once again, thanks alot for all your help.