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Thread: Weird tach indication problem

  1. #11
    Senior Member Delta Whisky's Avatar
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    Default Re: Weird tach indication problem

    The resistor is inserted in the tach line. I'm guessing the impedance of the RPM measuring circuit is pretty high so a high value, in-line resistor is needed to ensure spurious signal voltages are dropped below the measurement threshold.

  2. #12
    Spook712's Avatar
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    Default Re: Weird tach indication problem

    So in line in the + line?


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  3. #13
    Senior Member Delta Whisky's Avatar
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    Default Re: Weird tach indication problem

    It sounds like your system uses both of the tach leads. (I'm assuming we are talking about a Rotax.?) If that is the case, I'd try it there. Good luck.

  4. #14
    Spook712's Avatar
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    Default Re: Weird tach indication problem

    Yes, the instrument has a RPM+ and RPM- input


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  5. #15
    Spook712's Avatar
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    Default Re: Weird tach indication problem

    Problem solved, a 220Ohm 2 Watts Resitor did the trick


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  6. #16
    Senior Member Delta Whisky's Avatar
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    Default Re: Weird tach indication problem

    This is good news. Thanks for the update - one more tool in the tool box.

  7. #17
    Senior Member Maverick's Avatar
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    Default Re: Weird tach indication problem

    I bought my engine from salvage and the regulator is the original as far as I know. No entry in the logs about replacing it. However, I bought a B&C to carry in the plane based on recommendations made in another post. I have a GRT EIS and have not had any problems during this first 40hours and I don't have a resistor in the tach line. Given the proper operation now would adding a resistor now be counter productive or would it not be an issue with the current regulator. My concern is that I go somewhere, loose the regulator, install the new one and then find I have the issue with the B&C and need a resistor for the B&C.
    Fred
    EAA, AOPA
    KF5 (N49FK & N36KJ)
    Phoenix, AZ

  8. #18
    Senior Member Delta Whisky's Avatar
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    Default Re: Weird tach indication problem

    I'd go ahead and put the resistor in the tach line. It won't hurt anything and if your unit is susceptible as mine was (with the B&C unit) you'll be ready to go. Check out pages 14 and 15 of the GRT troubleshooting guide for more info. I'd also put the B&C unit in now and carry the original regulator as the spar. The B&C has a couple of features that sold itself to me - the most important being over voltage protection.

  9. #19
    Senior Member jiott's Avatar
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    Default Re: Weird tach indication problem

    Agree, put the resistor in now when it is convenient. Mine went about 500 hours before I needed to install a resistor.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  10. #20
    Spook712's Avatar
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    Default Re: Weird tach indication problem

    I got it on ebay


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