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Thread: electrical gremlins

  1. #1

    Join Date
    Aug 2012
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    LA
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    Default electrical gremlins

    The rebuild is done. The plane flies great, but somehow I have successfully added a few electrical abnormalities that I don't remember existing before the fender bender.

    I key the mic(pilot or copilot) and the rpm(rotax tach) increases 500rpm, the electric trim indicator lights go fuzzy and the voltage drops from 14v to 12v something.


    The strobes wreak havoc in my headsets. This noise goes away when I unplug the com antenna or simply turn off the com (garmin SL40). I have even gone so far as to remove the wingtip with the strobe installed, walked out of my hangar to the truck, plugged it up to my truck battery and I still get the noise!

    I can hear the transponder reply in the headsets as well. Noise does not go away with the com turned off. This may be to my latest re-routing of wire bundles to get everything away from the strobe wire. My intercom wiring may be in the same bundle as the transponder coax..

    I have a ground "mecca" as it has been previously described. Rg-400 coax, all shielded wire for the intercom. Battery has been on the tester and is strong. Com antenna is installed rear of turtledeck on factory mount option. Transponder antenna is installed under copilots seat with a 3" metal disk. Key West Regulator installed. Garmin Aera, Garmin SL40, Garmin 327 and PS-engin intercom all controlled by avionics master switch

    Anything common to all these issues? I'm going back to step one to confirm all grounds are clean and wiring is proper. I'm missing something....

    It's a good thing I fly from a non-towered airport so I can shut everything off and just enjoy the flight....

    KFIV-1200 Rotax 618
    Last edited by deejayel; 06-18-2013 at 09:09 AM.

  2. #2
    Super Moderator Av8r3400's Avatar
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    Default Re: electrical gremlins

    Sounds like grounding problems to me...
    Av8r3400
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  3. #3
    Senior Member HighWing's Avatar
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    Default Re: electrical gremlins

    Double check the Positive lead to the radio as well. Coax to antennas typically are not bundled and as I recall, if the runs need to be parallel, they should be separated by several inches and if crossing should cross at as close to 90° as possible.
    Lowell Fitt
    Goodyear, AZ


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  4. #4

    Join Date
    Aug 2012
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    LA
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    Default Re: electrical gremlins

    I spent many hours today troubleshooting this issue with some success. I rearranged my battery to frame ground, engine to frame ground and ground "mecca". I pined out the entire avionics and found nothing out of place. I bypassed the installed antenna coax by running an alternate coax outside the cabin to the antenna. I removed the antenna..same issue. reinstalled. hmmm.
    The problem simply goes away when I disconnect the antenna. Who needs a radio anyway...

    I did adjust the squelch break point in the SL-40. That took care of the strobe and transponder flicker noise.

    Then I took her out for a quick flight and now I need a new prop...

  5. #5
    Senior Member jtpitkin06's Avatar
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    Jan 2010
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    Greenville, TX
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    Default Re: electrical gremlins

    DJ,

    It sounds like an antenna short to me.
    The symptoms are that of an antenna short to ground.

    Disconnect the antenna and test between the inner lead and the outer connector body. It should be open.

    Try using a different antenna.

    Check the antenna connector on the radio mount for shorts

    John Pitkin KK5QI

  6. #6

    Join Date
    Aug 2012
    Location
    LA
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    Default

    Antenna shows resistance.

    I have a short pigtail off the sl40. Thought i had found the problem when i tested the end of the pigtail and found minimal if any resistance from the center conductor to the shield. Removed the pigtail from the tray and tested the plug on the back of the radio and had the same result. I thought it strange so i called my avi shop and he said that could be normal.

    I need to steal another antenna and try it. I have tested this antenna with another radio and it seemed to work fine, but it was a bench mounted "unicom" so it couldn't mess with other aircraft installed electrical systems

    Swapped antennas today. No change.

    Bench checking radio next

  7. #7

    Join Date
    Oct 2011
    Location
    Canada
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    187

    Default Re: electrical gremlins

    check your ground <- note that is not plural.

    I would not use the fuselage for a ground
    - this will rule out this issue.

    Separate all comm wires and power wires.

    use sheilded wires where ever possible
    - use high quality shield wire for your mag grounds
    and only ground one end or you will get a ground loop.

    Your antenna - is it grounded to turlte deck ?
    -is turtle deck grounded?

    Alot of this might seem trival but they all can/will add up to a huge problem.

    I have done thousands of comm instalations and it does happen but you need to rule out one by one.

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