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Thread: Not your typical flicker problem

  1. #1
    Constant Bitrate JPuma's Avatar
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    Unhappy Not your typical flicker problem

    Hi, I've been tackling a problem for quite a while with nosie on my screen. This is not your normal engine nosie, alternator nosie or bad ground nosie I've read here, it something much worse

    Basically I am seeing very faint nosie in the video. lines of movement. It seems to happen when the computer is doing things, I notice it more if theres video activity like scrolling songs in a play list. But its also can be when the screen is stactic. Think of the noise you hear when your plugged into analog speakers amd volume is turned up.

    Now, what makes this problem so complicated for me to put my finger on is this. This is the second computer in my car thats doing it. First was a moca 7043 and I was viewing it on my BMW nav screen. Since then I completely upgraded my system. New Sumicom 620, P1900 psu, EZpro power controller, EZTank, Tank battery and some other hardware not worth mentioning. I thought I was going to leave this problem behind but low and behold I was wrong. The problem still exists and even worse, or it was worse at first. I have tried many things, Ground wires up the wazoo even though I tought I had a pretty superior power setup. Still no go....In thinking it was some of the hardware I just had the computer hooked up to the psu with video and still no good. Hmm, then I thought, lets just hook the PSU up to the tank battery alone. Wow, clean video when not connected to the car. Okay, lets try the AC adapter powered outside the car...looks good again. Now try inverter and ac adpapter in car, still looks good. I saw some other noise differnt from my original problem like rolling lines but I guess the inverter shouldnt be too close to the pc. So I was able to get clean video with the interver and AC adapter. I was good for a few weeks and then I decided I didnt want to use my BMW nav monitor anymore, I want touch screen and crystal clear VGA ( this is what happens when you hang on this website). Besides, I hated having to use the inverter. I thought my problem would of went away when going VGA but that was wishful thinking. Still same video noise problem. I bought a Zenarc, btw.

    Oh, did I mention this happens when the car is off too. Okay, so ive been reading and reading and I tried a few more things. I put the VGA on a inverter and AC adapter (was using cig plug before) and the video was perfect. Now I am scratching my head, are you with me so far. I read about regulated PSU's and then proceeded to hookup the small OPUS POL dispite that some of your guys dont recommend it. Its safe to say that after two hours of having my computer running with car off the screen goes on without engine runnnig and looks as bright too. I have my screen turn on when key is turned, I like it better this way so of course the screen turns off when cranking. I may do the USB mod and if the opus gives me greif I have a ITPS I could replace it with. Okay so after I hook up PSU, still no luck same nosie problem.

    So lets break this down..the only thing that works for me is when the computer is running on its own power or when the computer and monitor is running off of seperate power sources. I suppose if I had a way to power the bme nav from another powersource the screen would of looked good too. The only PSU I tried so far is the P1900. I dont think its the psu, oh, I also tried a 20amp 12V noise filter from RShack. that didnt work at all. So if this is still a grounding issue I dont know where else to put a gournd except somewhere on the motherboard. The only thing I havent done is go into the pc and run a heavy gound out from the PCB. I dont think the case is gournded to the mobo well other then the ports in the back, ie VGA, USB, power. Sinice all of my tweaking and putting really good grounds in and grounding wires at their shortest distances it has improved the screen some but I can still see nosie.

    Sorry for the long post, been up all night and my carputer is still at 90%


    Any suggestings?

  2. #2
    phc
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    Here's my theory.

    You need to run 12V power from the PC's power supply directly to the LCD.

    The noise you are seeing is due to changing load on the PC's power supply (sounds like hard drive access), that you'll be hard pressed to filter out. That noise will travel up the VGA cable to your LCD.

    If your LCD is powered from your PC PS, then your LCD is getting the same fluctuations in power to match the VGA signal, so you shouldn't see it.

    Now if you power your LCD with an isolated power supply that floats, then that might work.

    Also I'd imagine that a good ground from the PC power supply directly to the LCD's power gound should do the trick also.

  3. #3
    Constant Bitrate JPuma's Avatar
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    okay, thats sound advise and worth a try. the 12v output on the P1900 is not hooked up to anything yet becuase when I moved to the inverter I used the ITPS I had for 12V power for my 1394 hub. I left it like this when I went back to the P1900. I also have the 5V secondary output in it as well so I am good to go in the 5V deptartment.

    Also, just to let everyone know the opus POL dosent really work well in 12V on the Zenarc. I have it powered by the cig lighter wires with ingition turn on. The screen has noise from the POL alone, seperate from the computer nosie. The POL is also making a buzzing sound which is consistant with the video noise.

    Phc, thanks for your input, I'll go and run some wires soon and test your theroy. I hope your right.

  4. #4
    Constant Bitrate JPuma's Avatar
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    Wow!!! Genius, very fundamental and was exactly the problem. Not sure how I would of fixed this with the OBM but now that I am going straight VGA this is a working solution for me. I am powering the VGA with the 12V on the P1900 and the picture does not show this power fluctuation anymore. I am going to try the ground method from PSU to VGA but I thnk I nailed it with the power from the PSU.

    Now I need to relay the power as well since I sometimes leave the computer running when the car is off. I have a 1 hour timer on my power controller if I dont turn the pc off myself. I like it better this way..... phc thanks for your help, I own you a beer!

  5. #5
    phc
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    Quote Originally Posted by JPuma
    Wow!!! Genius, very fundamental and was exactly the problem. Not sure how I would of fixed this with the OBM but now that I am going straight VGA this is a working solution for me. I am powering the VGA with the 12V on the P1900 and the picture does not show this power fluctuation anymore. I am going to try the ground method from PSU to VGA but I thnk I nailed it with the power from the PSU.

    Now I need to relay the power as well since I sometimes leave the computer running when the car is off. I have a 1 hour timer on my power controller if I dont turn the pc off myself. I like it better this way..... phc thanks for your help, I own you a beer!
    Glad I could help, but you actually confirmed my theory. I'm having a bit of the same issue myself ever since I put an 80W opus in my dash to power all the USB devices (DVD/CDRW takes 2 amps at 5V) as well as the LCD.

    I'm just about to rip into my dash again to see if I can fix it.

    -Patrick

  6. #6
    Constant Bitrate 00christian00's Avatar
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    Hey PHC,
    There is no other solution than that?
    I already have my opus overloaded,i can't put anything more on that.And i have to rip off all my car to recable the lcd to the opus.

    Thanks

  7. #7
    Constant Bitrate JPuma's Avatar
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    I have been pondering this some more and dont undstand why this works compared to other methods I tried. I mean, when I use an inverter on the LCD I didnt see the noise but when I used the cars unregulated power I did see the noise; two seperate power sources to the monitor. The only difference is the cars power also powers the P1900. In both senarios they both are still grounded by the same ground but in the monitor its through the USB and monitor cables.

    Also if this is a power fluctuation thing then why does it go away when I power the PSU for the computer with a different 12V power source (tank battery alone). There something more going on here then just power fluctuation from the computer. I think its more like feedback on the power line, or maybe freqency noise on the power line given off by the computer (same thing?). Is there a way to check this using an oscilloscope? if so isnt their a filter that can fix this?

    not sure why the PSU's 12V is able to filter this out, maybe its desigend to. Is it possible that the computer is pulling down the 12V car power in such small doses that it doesnt hurt the anything but can be seen in the monitor, sort of like theres AC on the line? (god, I wish I continued passed ohms and voltage law in tech school).

    How this for a theory, what if we put a diode on the 12V line feeding the PSU, if theres any power "feeding back" on the 12V line from the computer then it wont infect the entire 12V system in the car? If its frequency thats feeding back, wouldnt there be a way to filter this? mind you, this is all speculation and I may be way off base. Maybe this will prompt someone who is EXTREMELY knowledgeable in this are to speak up.

    For me the problem is solved but what if I want to add more monitors in the foreseeable future (headrests?) If the 12 line in my PSU cant handle them all I will need to look for another power source and I dont want to use an isolated power/inverter solution. Also, it would be nice to use my OBM now in conjunction with the VGA.

  8. #8
    phc
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    I believe your AC inverter has built in isolation. And when you connect the LCD to an isolated battery, the problem goes away. Sounds like ground loop problems.

    If your OPUS is already maxxed out, then in my best guess, you will need an Isolated DC/DC converter. Use car power for the input, but the output is isolated. Don't tie the ground of the isolated output to anything, let that happen in the LCD.

    Normally this isn't an issue because your standard video monitor (running on AC power) probably has built in isolation.

    Video noise is a complex thing to sort out. Much of the issue here is in the ground. Noise on the ground will get everywhere, you cannot filter it, unless you filter everything, each of the RGB signals in the VGA would need its own filter, plus the power. Something like a low pass Chebyshev Filter.

    I don't think diodes are fast enough to filter out the frequencies we are talking about. If your VGA is 1024x648 x 60Hz refresh, then your vertical scans are at 38.8KHz, horizontal at 40MHz (if I've done my math right). The scrolling noise you see is happeing near the vertical scan rate.

  9. #9
    phc
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    Some DC/DC Converters

    http://jameco.com/webapp/wcs/stores/...07&pa=155707PS

    Also, check out datel.com

  10. #10
    Constant Bitrate JPuma's Avatar
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    Thanks, I think I cam accross these in the past. So how are you going to solve your problem. Have you done anything yet?

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