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  • Help : Monitor interference problem

    Ok well the problem is I'm getting really bad interference in my monitor. Scan lines coming across, darkened display, and it will turn completely off when the bass hits hard.

    I took my laptop out to my car and set it in the trunk right next to the carpc and hooked it up to the same VGA cable as the touchscreen and it worked fine, no interference, even with music blasting. This tells me that it's not the routing of the VGA cable that's the problem.

    So then I take the whole CarPC inside and test it on a real ATX power supply, no interference there either, which tells me it's not a problem with the motherboard.

    Where do I go next from here? Keep in mind there are a few other strange symptoms : One of them is that I get really really bad alternator whine (high pitched noise in speakers varying with engine RPM), but it only lasts until the computer's sound card turns on, the minute the sound card is active it goes 100% completely away. The other thing is that sometimes the computer will randomly reboot, I believe this is caused by severe voltage drops due to my very much lacking electrical system attempting to power about 2500W of electronics and sound equipment.

    Do I have reason to suspect the power supply? (OPUS 150W DC-DC) or should I blame it on my wiring? How and what should I test next?

  • #2
    Sounds like a ground problem, I had similar issues with my laptop in the car.
    Checkout the Car audio section of the forum, there is a sticky in there that explains ground loop problems and how to trouble shoot them.

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    • #3
      Yeah it definitely sounds like a ground loop, however I don't understand why if it was a ground loop the audible noise would go away once the sound card powers up and the monitor noise would go away with a new PC, same power cables, same signal cables...

      I'm starting to believe that the problem lies in my power supply. In both cases where I was able to get the noise to go away, the only thing that was bypassed was the power supply. With the laptop I bypassed the whole pc and used the same wiring which eliminates the wiring as the source of the noise, and when I tested it in the house the only thing I eliminated was the power supply, which eliminates the PC its self as the source of the noise.

      Today I'm going to take a really long extension cord outside and hook up my regular ATX power supply that I used for bench testing the PC inside and try that in the car with everything else running (including the OPUS PSU) and if I still have noise I will unplug things, starting with the DC PSU.

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      • #4
        Update : I took an extension cord outside and hooked up a regular AC ATX power supply to the computer...

        The audible noise was actually far worse, but once again when the sound card activated, it went away completely. The monitor distortion was also completely gone.

        Any ideas?

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        • #5
          Did you ever think that maybe the voltage is dropping to your monitor when you have your stereo cranked?

          You could try powering off your computer power supply instead of direct...but since your computer is losing power also...

          Maybe you need to figure out a way to keep the voltage up...bigger alternator, second battery, a cap for your subwoofer amp etc.
          current projects

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          • #6
            When you had your laptop hooked up to the screen, was the carpc running too? If there is nothing being drawn on the power cables going to your computer, then no interference will be caused.

            I think it is a cable interference problem.
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            • #7
              Power your carputer from the same points as your amp. Connect the positive terminal of your PC to the positive of the amp and the negative terminal of the PC to the negative terminal of the amp. Getting a bigger alternator does not alway solve power problems. BTW Is there any distortion in your bass when it's playing. if there is you should check the wiring which connects the sub amp to the battery. Also check you headlamp for dimming (with and without the engine running) and get back to me.

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              • #8
                Here is basically how the wires are setup.

                I have two 4ga wires running from the battery to a buss bar located underneath the rear seat. That buss car has one 4ga wire going to the 1200W mono amp, one 8ga wire going to the 400W 4-channel amp, and one 14ga wire going to the computer's power supply.

                There is a second buss bar, which is exactly like the power one, except backwards. 3 wires run from the grounds of the amps (same gauge wiring) to the buss car, and then there are two 4ga wires going from the buss bar about a foot and half to a ground point. The ground point is directly in the center of the car, on the floor, it was completely sanded down and drilled (not a factory bolt or anything)

                One remote wire (16ga I think) runs from the ignition column and then splits to trip the relays in both amps and the PSU.

                The buss bars all had plenty of surface area to, they are all clean sanded down aluminum which metered at zero resistance.

                Here's some pics...











                As you can see, I did the best job I could keeping all of the power wires tied up together, and shoved as far away from the outside of the trunk as I could get them, while all the signal cables (which for the time being aren't neatly tied up) are running along the outside of the trunk and never crossing their path.

                I do not believe it is a wiring issue because when I used the laptop there was no monitor noise despite me using all the existing wiring (all amps were powered up as normal)

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                • #9
                  Are those pictures of your positive power wire busses? Make sure you keep plenty of marshmallows on hand.

                  Ok well the problem is I'm getting really bad interference in my monitor. Scan lines coming across, darkened display, and it will turn completely off when the bass hits hard...

                  ...took my laptop out to my car and...

                  ...test it on a real ATX power supply, no interference there either...

                  ...The other thing is that sometimes the computer will randomly reboot, I believe this is caused by severe voltage drops due to my very much lacking electrical system attempting to power...

                  ...Update : I took an extension cord outside and hooked up a regular AC ATX power supply to the computer...

                  It looks to me that you have proven the problem over and over. You don't have enough power.

                  If you have an external video card installed...then try your system without it. On mine, I could power a Geforce4 card...but not an ATI all in wonder...with the 120w Opus.

                  Hook a voltmeter up and watch the voltage when everything drops out.

                  Also have you wired your Opus up EXACTLY the way the instructions say? (all the yellow wires to +12v, all the black to GND) Do you have a heavy cable from the opus to your +12v?
                  current projects

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                  • #10
                    First of all I'm know what I'm doing, so I don't think the marshmallow comments are entirely necessary. One buss bar is for positive and one for grounds. In case you didn't notice both bars are bolted to a piece of wood which raises them off of the chassis and the positive wire has about 4 layers of sound deadener underneath it just in case somehow it gets bent in enough that the bottom of one of the bolts could touch the chassis.

                    Also I'm sure the voltage issues aren't helping however I don't believe they are the entire cause of the problem. I'm well aware that my audio system draws more amperage than my alternator can dish out which causes the load to jump to my battery, however I never draw full power (play music really loudly) for long enough to significantly drain my battery. I've tested the battery engine off and it reads 12.X volts so it maintains a charge just fine. The other thing is that the OPUS power supplies are made specifically to withstand voltage drops, the manual says they can operate steadily between 8-19 volts. I've never gotten anywhere near there even with the amps drawing from the battery on bass hits. Also the final thing is that the interference is always there, not just when the amps are on or when music is playing. It does get worse when the amps draw lots of power, but it's bad enough to the point of the PC not being usable even with music off. I have not yet tried running the computer with the amps completely disconnected yet though...I'll give that a shot tomorrow.

                    Oh and yes my PSU is wired correctly, this system has been functioning flawlessly for over a year now with the only modifications being the audio system and wiring. The interference problem just showed up in the last few weeks and without changing a thing went from annoying to crippling.

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                    • #11
                      The screen blanking out and dimming is not interference.

                      Some fine wavy lines in your video could be caused by RFI...but it becomes very hard to tell from what.

                      Your alternator can produce RFI (you said you heard alternator whine)...but it could be your ignition causing the RFI...a high voltage drop across a 3' wire.

                      In addition your power supply can produce RFI.

                      Ferrite chokes might help if your problem is HF AC riding over your DC cables.

                      As far as your +12v buss goes. It appears to be half an inch above the metal frame of your car...and what is above it?

                      You could have a thin piece of metal touch from your buss to ground, it wouldn't create enough amp draw to blow your fuses (I hope it is fused at the battery) but it will turn white hot and ignite anything flammable nearby (nice dry carpet fibers...or plastic sound deadener) before it melts away.

                      Because of where you have located your buss...you need to physically protect it from the top and bottom...not simply by distance. As a minimum stuff the whole thing in an inner tube. (but take a look at the commercial offerings...nice protected assemblies)

                      You have a half inch piece of wood there...but how far is the screw that holds the buss to the wood from going out the other side of the wood? it is a lot less than half an inch...and wood spits, so now you will have that screw vibrating along rubbing its way through the rubber and paint until it starts sparking.

                      Have you noticed any other bare +12v wiring, anywhere in your car...other than the tops of the battery (and even those have a cover)?

                      It's your car...but it would be a shame to go through all that work and lose it due to an interior fire.
                      current projects

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                      • #12
                        I have a couple more ideas for tests I want to try...

                        I'm going to take a regular monitor outside and hook it up with an extension cord to the carPC being powered by the car and see what happens.

                        I'm also going to completely disconnect the power to both amps and run just the PC and see what happens.

                        It's been raining for the last 3 days and I don't have an indoor work space otherwise I'd have already done these tests and had the results. It's also been a few days without running the computer or the amps so my battery should be nice and charged by now if that was in fact the culprit.

                        I also found a local guy who is friends with my dad who can rewind my alternator, I think 250 amps should be sufficient for a 1200W amp, a 400W amp, and the computer. Yes I know, smaller pulley for higher idle amps with peak being reached at normal driving RPM.

                        Also Cummins, I understand your concerns about the buss bars, and I think I'm going to correct some of the issues by just removing them I put them in because I kept buying/selling/trading equipment and building new boxes and moving stuff around just about every week and it was a pain to redo all the wiring each time, so with the buss bars in place it was just a matter of removing a few bolts. I have all my equipment finalized now, so they can go. Anyway, I'm going to rewire all my engine bay with 1/0, I'm going to run 1/0 to the 1200W amp, and 4ga to a distro and then to the 400W amp and PSU.

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                        • #13
                          Ok so I guess the only thing I can do is overhaul my electrical and hope for the best.

                          I'm going with all knukonceptz kolossus wiring.

                          I'll start with 1/0 under the hood, replacing the alternator/battery/ground wiring to get the most out of my alternator. (If I still notice voltage drops I'll have to alt rewound in the near future)

                          I'll run 4ga for the 1200W amp, 8ga for the 400W amp, and 10ga for the PC. Of course they will all have same gauge grounds to a common ground point.

                          I'm going to buy better signal cables. Right now I have a headphone jack splitter coming out of my PC which then has two of the cheap 6 foot long 3.5mm headphone to RCA splitter cables, even though they only need to go about 1 foot.

                          If after all that I still have noise, then I'm positive that it's the OPUS causing the noise and I'm going to try my best to warrant it.

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                          • #14
                            Ok so guess what, I figured out what the problem was.

                            The bolt that held every single ground in my system to the chassis came loose. It was still in enough for everything to power up, and with all the wires coming from it I couldn't tell just by looking that there was a problem. Somehow, all the times I checked the wiring, I never noticed it, and I probably wouldn't have if I didn't accidentally pull on the wire.

                            Tightened it up, every single bit of noise/interference in the sound and video is completely gone. Somehow it got completely stripped out so I'm going to have to relocate the grounds to a new spot, but all is well and I luckily held off ordering my $150 worth of new wires

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