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Thread: Electrical interference on monitor, out of ideas, will pay $20 to my savior

  1. #1
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    Electrical interference on monitor, out of ideas, will pay $20 to my savior

    I posted this in the power supplies thread but wanted to cross-post here since it's relevant.

    I have a P2140 and am having an electrical interference issue that I have not been able to solve despite several attempts.

    What does it look like

    The electrical interference occurs in the monitor as multiple horizontal lines dancing up and down the screen. It occurs on all inputs (VGA, RCA) and across multiple different monitors I have tried.

    What causes it

    It occurs ONLY when the laptop (ThinkPad R60) is running AND being powered by the P2140 at 17V using the supplied additional resistors.

    What makes it go away

    1. When the laptop is powered from the wall in my garage with the stock AC adapter and all other connections unchanged, the interference is gone.

    2. When the laptop is off, the interference is gone. As soon as the laptop boots up, the interference is back.

    3. When I remove or re-insert my PCMCIA sound card, the CPU cycles go up temporarily and the noise is gone for 2-3 seconds but then comes right back.

    What have I tried

    1. Grounding: Single grounding block for the monitor, the laptop, the 5V rail for USB, the PSU, and the amps. Also tried grounding the metal of the laptop chassis to the same grounding block. Grounding block feeds via a 4ga cable to a sanded, solid, single ground point drilled into a seatbelt bolt. I have tried a different ground point in the trunk with no change. Just for testing, I also tried individual ground points for the monitor and laptop with no change. I have no noise in my audio system, no alternator whine, and no static.

    2. Decoupling capacitor Tried both a .01uF and .001uF decoupling capacitor linked between power and ground for the laptop. Also tried both between power and ground for the monitor. No change in intereference.

    3. Disconnecting everything from the laptop All USB devices, sound card, docking station. I left just the VGA output connected and the interference still persists.

    4. Disconnecting the monitor inputs I thought the interference may be coming over the VGA or RCA line, which are run on the opposite side of the car from the power wires. Even with the VGA disconnected, the noise persists on the RCA input (rearview camera), and vice versa. Just the fact that the laptop is on causes interference in the monitor even if there is no video signal going from the laptop to the monitor.

    5. Ferrite cores/beads Have tried them on the power to the laptop, monitor, 5V rail, and the main input to the P2140.

    What now?
    That's what I am hoping someone can help me with. As far as I can gather, the power output of the main rail on the P2140 is CAUSING interference in the power to the monitor, but only when the laptop is on and active. So then I would think - faulty/crappy mobo on the laptop. But plugging it into stock AC adapter from the wall, and all noise is gone. I have searched every thread over the last several years that I could find for a solution, and nothing has helped.

    I am OUT of ideas.

    $20 via Paypal to whoever can give me a solution that works. I am serious
    Last edited by hari-bhari; 01-12-2014 at 11:11 PM.

  2. #2
    Low Bitrate ephect's Avatar
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    does this happen with the engine running and without the engine running?

    does the interference happen with the laptop is running on battery only? if not, i would say its ur power supply for the laptop is the cause

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    Thanks for the reply.

    The issue occurs both with the engine on and off.

    There is no battery in the laptop, so I cannot answer that question.

  4. #4
    FLAC SNOtwistR's Avatar
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    Have you tried running a ground wire to the metal shield around mainboard of laptop? As in really grounding the laptop not just through the power socket but to the inside guts of laptop. Just a thought SNO

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    Quote Originally Posted by SNOtwistR View Post
    Have you tried running a ground wire to the metal shield around mainboard of laptop? As in really grounding the laptop not just through the power socket but to the inside guts of laptop. Just a thought SNO
    actually yes, i forgot to mention that. i did find a different metal point in the laptop chassis and grounded that. no difference.

  6. #6
    FLAC SNOtwistR's Avatar
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    I only have 3 things left on my check list. Have you ran a ground wire from battery to computer power supply "in" negative wire, not using chassis as ground. If you have and no change then have you tried a bigger cap on input and output other than the .01 you tried. I personally like around 10000uF 25v on a 12v system it can provide 4-6secs depending on the load. Or maybe if they don't fix try an inductor say around 100uH 3-10amp again depending on load. OldSpark will know more on the actual requirements as I am just an old electronic fiddler not trained in anything. Hope this helps SNO

    p.s. please take off the paying part, I know you want it solved but forums work on free information and help as far as I am concerned. I think most people get the enjoyment out of helping if they can. just my 2 cents
    Last edited by SNOtwistR; 01-13-2014 at 12:29 AM.

  7. #7
    Constant Bitrate eugenweij's Avatar
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    If you still have the battery , try putting it in. it may help straighten out any noise coming from your power supply.

    as far as I know when you put in a battery the power from the supply goes to the battery and from the battery to the mobo , it may be a long shot but couldnt hurt to try.
    View my worklog here

  8. #8
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    i also have noise on my LCD, so i can understand where you comming from... ....
    1), first, be sure that no metal parts of your LCD touch any metal parts of your dashboard...
    2) in my case, running a Bigger wire from the alt to the back battery (although, the power consumptions would require a way smaller), helped reduce the noise allot! (but that was , for the noise, that came in ONLY when the engine was running)
    3) try to run a shorter VGA cable. no better quallity. just shorter... in my case, when i tried a 1.2m, it made the noise completely disappear (although, you cant use so small cable IRL)

    if you cannot solve it, but you are ok with just hiding it, you could try
    either chargin the laptop from a DC/AC inverter, and then use the stock charger (Which is not a power efficient way, AND may cause additional noise, instead of solving it)
    OR
    why do you need to charge the laptop when it's working??? you could have the laptop being charged, always when the engine is not running, and when you start the engine, cut the charging, so the laptop works on its own battery! if your laptop has at least 2hours life, then its no problem!!

  9. #9
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    I had success in significantly reducing interference (but not completely, some minor flicking on Windows boot screen) by wrapping my VGA cable in aluminium foil, and routed it through my dashboard no-where near any power lines.

  10. #10
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    You might try using copper tape and solder a drain wire from the copper to ground (Farady shield)

    You might also try "desensitizing" the VGA lines by loading them with a resistor to ground.

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