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Maybe grounding issue? Scratching my head.

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  • Maybe grounding issue? Scratching my head.

    Beyond this current issue, I have no issues with grounding or power.

    My setup has always had a power run with 4g to a distribution block feeding a bunch of audio stuff and dcdc to the computer. Then ground back to distribution block with 4g to chassis.

    I have never noticed any issue with my lilliput in my setup. However, recently I tied my navigation screen into the setup for a dual screen setup and I notice some wavy lines almost as if the refresh rate is wrong. It gets worse when I turn up the bass. I only notice this issue with the nav screen when it's receiving the feed from the computer, everything is fine when the nav screen is in its standard mode. And I never notice any issues from the lilliput screen at all. So what could be the issue?
    I would say its the cars grounding to the chassis, but no problem with the screen in regular mode.
    Then I would say its the grounding of the computer, but no problems on the lilliput.

    The way the computer is specifically grounded is through the dcdc USB, from that with the wire it came with, soldered to a 6g, and that to the distribution block, then a 4g to the chassis.

  • #2
    do you have any inverters on your system? i also found the same problem when i installed my second screen, and i pin-pointed that the noise is being induced through the VGA cable. if that is the case, then maybe a vga to HD and then HD to vga converter would help (although its way too complicated for something that might be simpler) are the lines static, or do they change Frequency?


    • #3
      I presume the nav screen does not have the same ground as the computer - ie. dc-dc USB output/computer GND else (maybe) the DB GND?

      If not, try those solutions (USB output preferably?).

      If it's a big audio system, move the computer GND to whatever the nav is using - ie, you want the computer & nav to have a common GND which is unaffected by the audio/amp GND (and hope that doesn't create other ground loop issues if signal interconnections exist).


      • #4
        How much power does your audio system use? And how far is the positive wire traveling to the block? 4 Gauge seems small to me for any sizable system especially if you are splitting off from it and especially if you are going all the way to the trunk with it.

        Take a voltage measurement if you can from the positive block to the ground block and from the positive block to your navigation ground.

        It may be a wiring issue, corrosion on one of your blocks, or a shielding issue.

        You don't really mention how you are connected to your Nav screen or exactly what that screen is. Is it a factory screen and you are using the backup camera input or did you hack it with an aftermarket unit to allow you to use it as a computer screen? Is it an aftermarket NAV unit that allows you to have external video?


        • #5
          Settra, I dont have any inverters. also, I don't understand your question of if the lines are static or not.

          Oldspark, no, the nav screen has all factory wiring and grounding. Besides that, I don't understand what you are saying in the first two paragraphs. Finding the nav screens ground is kind of out of the question. I wouldn't know where to begin, and the amount of pulling up of the dash I would have to do to find it, It's not really worth it unless this issue would actually damage the screen. With the notion of just separating the audio and computer ground, would moving it to a different grounding point in the same area help? Ex. The backrest of the back seat has a grounding point on the left and right. If I keep the audio on the left and the computer on the right, would that be ok? Or is the backrest as a whole considers THE grounding point? Also, won't that cause a ground loop since I play my music through the computer?

          Redheadedrod, I believe I'm running 900wrms. The power is traveling about 16ft. If you mean take the voltage by putting the positive lead on the positive D block and the negative lead on the ground D block I'm getting 12.5V-13V. It's not a corrosion issue. Shielding issue I doubt, but how would I narrow it down. If it is a shielding issue, it's not a problem with the RCA or VGA wires, I already eliminated those potential causes.
          It's the factory nav, hacked with a naviks system with a custom harness to allow the feed with a switch.


          • #6
            Given it's an OEM nav then I'd suggest trying with the computer running from the battery +12V and GND (-ve terminal) else its nearby chassis/body GND. That might decrease the problem if not eliminate it.

            It's probably a case of "ground loop" problems which can be from different GND voltages due to currents in the GND conductors or circular loops (eg, due to amp to PC or HU signal grounds), or radiated noise (from GND cabling or other sources).
            redheadedrod is covering the same causes but to more detail (ie, taking measurements).
            settra is also covering the same, but specifically the problem cased by inverters and their current pulsations (hence ground loops or radiated EMI). And amps are no different to inverters wrt to their power/PSU inputs.

            I'll leave it to the others to solve your problem.


            • #7
              You can take a measurement of the voltage and use the Positive D block in both cases. For the ground use the negative D block for one and a point under the dash for the other unless you can identify the ground in your hookup. They should read the same otherwise you definitely have a ground loop problem.

              In your case a ground loop problem may be hard to fix because you are trying to use an OEM integrated piece and an aftermarket unit.

              However another issue might be related to your VGA cable. I am assuming you are using a standard VGA cable. In a noisy environment like a car you may need to use a better VGA cable to shield the Rf from inside the car. You may need to ground the shielding to your car body. You may also have an issue of the cable being too long. Some video cards can't drive a VGA screen much more than 6'.

              A common suggestion to fix audio problems is to use an external USB sound card. You may be able to try the same thing in this case with a USB video card driving your NAV unit.

              With this you would then use a very short VGA cable between the video unit and the NAV unit. Since the only issue you have is the Nav screen this might be a viable solution for you. Because it is a short run for the video it shouldn't pick up much if any RF. The graphics card should be more than powerful enough to run your NAV screen and the USB cable is pretty immune to noise because of the design and technology behind it. With a quick search I found the following USB VGA graphics "card" and at $45 it is pretty cheap assuming it will work for you. If it doesn't work for you, you can always return it saying it wasn't compatible with your computer.

              This card seems to only have a USB and a VGA connector on it and no need for an external power supply.:


              • #8
                if the lines (the noise) are going up and down, or are at one point. if they change their frequency (more hammin or less hamming. think of it as diferent noises in the noise on speakers) .
                anyway, although i think oldspark says the same , you could try powering the screens directly from the pc PSU!


                • #9
                  It's definitely a power/grounding issue and not interference in the wire. I tried it out with my laptop on its own battery and no issues. I'm going to first run a ground wire straight to the battery and test it to see if it goes away. If that works ill try to find a different grounding point in the trunk. If that doesn't work ill just make a permanent ground to the battery. My question on that now is, does it make sense if I have to do that and it causes a ground loop, to keep the ground to the battery as well as the existing d block? Would that eliminate the ground loop and also the interference?



                  • #10
                    If it eliminates the problem then don't interconnect that GND to the block.
                    (1) there is no point & (2) it then shares that same GND and the problem will return.


                    • #11
                      I did it and the same problem continues. I know it's not any wires picking up anything because I didn't move any wires except the ground in my following tests. First I took a laptop and made the connection using its battery, everything perfect. Then I took a the original ac connection that came with the computer and plugged it in to ac, and everything good except for a slight 60hz hum bar (nothing crazy). Then I took the original hook up, took the ground wire, ran it from the dcdc usb straight to the battery on the outside of the car, everything came back. I'm thinking the power line could cause this, but that doesn't make too much sense. Also, could the dcdc usb be the culprit? What next?


                      • #12
                        Also, I verified, I'm getting 13.7v steady, not moving or playing music. With base hitting I drop to 12.7-13v. I discoed the entire audio system, so there is absolutely no draw from the D block except the computer. And I took the ground straight to the engine block. Note, the ground that I used for this testing is two 16g wires.
                        Last edited by Champak; 07-05-2013, 05:50 PM.


                        • #13
                          The ground should not be the engine block - no vehicle/cabin loads use that; they'd use chassis/body (or fusebox) else the battery -ve.

                          The key is using the same ground, and separating low current ground (paths) from high current grounds.
                          After that, it's cross-grounding and induced noise problems.


                          • #14
                            I just read what I wrote, to clear up, I tested the ground (running on the outside of the car) to first the negative terminal and then to the engine block. The terminal caused the same problem. Sorry i wasn't clear before. And since the ground was on the outside, that would eliminate any induced noise pick up right? I also thought by going to the battery, that would automatically eliminate all ground loop and noise problems...not true?

                            If I discoed the power of the entire audio system, shouldn't that have eliminated the difference of high/low current ground paths? I assume (yes it's bad to assume) that the power draw from the amp and stuff would make the high, and that gone everything should even out, or at least get better.

                            So I guess I really have to go searching for the nav screens grounding point huh? If the problem is still there, what is cross-grounding and how do I fix it?


                            • #15
                              By cross grounding I meant what I call earth or ground loops - namely a loop connection of GNDs.
                              EG - a heavy GND from batt- to amp and a separate GND to the HU, and then an HU to amp interconnection that interconnects their GNDs. That is literally a loop.

                              Such gnd loops can be a PITA in domestic systems because they are prone to circulating currents from AC fields (eg, 50/60 Hz hum).
                              If you were like me, you would NOT expect the same in a vehicle because there is no "external" AC and a vehicle body may provide a lot of shielding. But "gnd loop" problems still occur because of gnd currents which cause equipment gnds to be at different voltages.
                              And then there is the noise - whether conducted or radiated - caused by changing currents and noisy DC lines.
                              And since there is lots of current switching occurring in a vehicle - whether it be their CPUs and digital equipment, dc-dc converters (PCs, mobiles, amps etc), inverters etc - there is lots of scope for line (DC) and radiated noise.

                              Hence why there are many solutions. HUs might be powered direct from the battery for "cleanest DC". (The battery is the biggest capacitor in a typical vehicle and does the most AC filtering.)
                              Heavy grounding (fat or short cables) may be used to reduce GND voltage drops. Single point or separate grounding for low current stuff like sensors and audio signals (ie, separate to power GNDs).
                              Breaking RCA shields/gnds at one end may break some loop problems, otherwise gnd isolators may be used.

                              So, by running your GND external to the vehicle, do you think you eliminated GND noise or caused more noise? (The answer would depend on your particular situation.)

                              Note that I don't consider myself anything of a GND loop expert - I'm just reciting some of the basics. (And my knowledge of noise suppression and shielding for analog transmitters etc is mostly irrelevant these days.)