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  1. #1

    Default Tachometer not getting signial.

    My tachometer is not receiving a signal from the engine. Where on the engine would the sending wire hook up to?

    I have a
    1990 Johnson 70 hp VJ70TLESB Outboard Motor

    Thanks

  2. #2

    Default Re: Tachometer not getting signial.

    Gray wire from the rectifier. Do you have the harness that plugs into the controller? You could have a bad rectifier or tach.

  3. #3
    Join Date
    Sep 2016
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    Smyrna, TN
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    236

    Default Re: Tachometer not getting signial.

    Voltage from the gray lead at the rectifier should be 9 volts + or - 1 volt at 1000 RPM. Just above an idle since you don't have a tach. See pic for your rectifier. Reference #63 is the rectifier. Should find the gray lead there.


    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  4. #4

    Default Re: Tachometer not getting signial.

    Thanks. Thatís what I was thinking. Iíll check it out.

  5. #5

    Default Re: Tachometer not getting signial.

    Thanks for the info. I’ll check it out.

  6. #6

    Default Re: Tachometer not getting signial.

    Finally got around to test old rectifier. It was bad. Replaced it and went out last night. Success. Thanks for the the help.

  7. #7
    Join Date
    Apr 2010
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    Default Re: Tachometer not getting signial.

    t2stroke, is that 9 volts for the tach AC or DC ????

  8. #8
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    Sep 2016
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    Default Re: Tachometer not getting signial.

    I believe that is rectified current so DC. Same lead as going up to the tach.

  9. #9
    Join Date
    Apr 2010
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    Default Re: Tachometer not getting signial.

    I always thought that was AC current seeing it comes off of the stator.

  10. #10
    Join Date
    Nov 2011
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    tennessee
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    Default Re: Tachometer not getting signial.

    Comes off rectified side of bridge rectifier and is DC......
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  11. #11
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    Apr 2010
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    Default Re: Tachometer not getting signial.

    I just looked at a wiring diagram and the tach comes off of the board before the rectifier.

  12. #12
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    Nov 2011
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    tennessee
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    Default Re: Tachometer not getting signial.

    Here is Faria troubleshooting and they state 2 volt DC or more when testing???

    faria-instruments.com/site_manuals/IS0100_Tachometers.pdf
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  13. #13
    Join Date
    Sep 2016
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    Smyrna, TN
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    Default Re: Tachometer not getting signial.

    ​I am use to texting primarily 35amp big motor systems which is why I quote the 9 volt + or - 1 volt spec. Guess I should clarify that as to what system you are running.

  14. #14
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    Apr 2010
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    Default Re: Tachometer not getting signial.

    On the yellow wires coming from the stator, is that AC or DC voltage ??

  15. #15
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    Default Re: Tachometer not getting signial.

    The two or three wires coming out of the stator is A/C voltage and the rectifier or bridge converts it to D/C. The tach counts the pulses per revolution same as a diesel engine uses the alternator pulses before it is rectified into direct current.

  16. #16
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    Default Re: Tachometer not getting signial.

    Meaning the tach runs on AC current ??

  17. #17
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    Default Re: Tachometer not getting signial.

    It runs on the pulse per revolution. If the stator puts out 6 pulses per revolution multiply that by 700 rpm equals 4,200 pulses per minute or 70 pulses per second at idle speed. Its kind of amazing to me a tach can count the pulses per second at 5000 rpm thats 500 pulses per second! At least thats my understanding on the physics.

  18. #18
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    Default Re: Tachometer not getting signial.

    Does that mean AC or DC current ????

  19. #19
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    Default Re: Tachometer not getting signial.

    The stator is the same as a alternator it puts out A/C current before the regulator but i believe the tach uses a diode to turn it into a D/C pulse same as the coil neg on a inboard engine.

  20. #20
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    Default Re: Tachometer not getting signial.

    DC pulses. They tap in to a point that gives half wave rectification; the voltage pulses from 0 to some voltage (9? or whatever) but always the same polarity. That makes DC pulses that the tach "counts".

  21. #21
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    Default Re: Tachometer not getting signial.

    I was told years ago by an instructor in OMC school that tachs hate DC voltage but function on AC, so always check your wiring if you have a tach problem. O'well, I think I'll just give up on this. !!!!!!!!!!!!

  22. #22
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    Default Re: Tachometer not getting signial.

    The signal wire is not current it is only one half of a sine wave think of it as a switch being turned on and off really fast.

  23. #23
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    Default Re: Tachometer not getting signial.

    Well I guess then that the AC current that runs my refrigerator, furnace, stove and ect is nothing but a bunch of half sine waves ????

  24. #24
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    Default Re: Tachometer not getting signial.

    Quote Originally Posted by Boobie View Post
    Well I guess then that the AC current that runs my refrigerator, furnace, stove and ect is nothing but a bunch of half sine waves ????
    you evidently have never used an oscilliscope to make that idiotic comment.

  25. #25
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    Default Re: Tachometer not getting signial.

    Click image for larger version. 

Name:	Half-wave trace 1.jpg 
Views:	4 
Size:	18.9 KB 
ID:	18082Top trace is your household AC, bottom trace is half wave trace. You can see how the half wave creates a series of pulses. In an outboard, the faster the flywheel magnets go by the stator coils, the closer together the pulses become. The more pulses per second, the higher the tach reads.

  26. #26
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    Default Re: Tachometer not getting signial.

    If you have a ohm meter that measures Hz you can use it to read rpm. Just put a probe directly in the pos terminal and hold it close to a plug wire. For a two stroke multiply it by 60 and for a four stroke multiply it by 120 i tried it and it works very accurateiy.

  27. #27
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    Default Re: Tachometer not getting signial.

    No body has told me yet it is AC current the tach runs off of. Soooooooooooooooooo I give up !!!!!!!!!!!!!!!. Thank you all for your time.

  28. #28
    Join Date
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    Default Re: Tachometer not getting signial.

    Quote Originally Posted by Boobie View Post
    No body has told me yet it is AC current the tach runs off of. Soooooooooooooooooo I give up !!!!!!!!!!!!!!!. Thank you all for your time.
    All I can say is that the voltage regulator on my 90 hp Johnson went bad - so I bypassed it, and ran directly from the battery for a couple of seasons.
    I had hooked up my tachometer lead directly to one of the stator leads, and I grounded the other stator lead with a jumper wire.
    Tachometer worked perfectly during that time.
    I reconnected everything in the normal way once I had a chance to replace the voltage regulator, and the battery is charging and the tachometer works fine.

    So yes, the tachometer will run off of AC current.

    CarMech1969
    Last edited by CarMech1969; 06-22-2018 at 09:27 PM. Reason: typo

  29. #29
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    Default Re: Tachometer not getting signial.

    Quote Originally Posted by Boobie View Post
    Well I guess then that the AC current that runs my refrigerator, furnace, stove and ect is nothing but a bunch of half sine waves ????
    I talked it pver with my associates Boobie.... we think it's broke!
    We occasionally have questions. If you fail to answer, it may affect ours.

  30. #30
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    Default Re: Tachometer not getting signial.

    Thank you Joe ! And CarMech ! CarMech. It makes me feel good for what you said in your come back. Proves the tachs run off of AC voltage.
    Last edited by Boobie; 06-22-2018 at 11:17 PM.

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