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tach operation

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  • tach operation

    i have a j140tlcte 1983 model johnson the tach stoped working checked rectifier was bad so ordered one meanwhile i read to move the tach wire to the other yellow supply wire from stator tach worked while i waited on new rectifier can someone explain how this worked?

  • #2
    Guessing here a bit...........The diode that failed in the rec module failure mode was probably a short/low low resistance fired pn junction. The tach signal wire (gray) is jumpered on the terminal block (see below) such that it is wired to the side (two sides available, Both AC, yellow and yellow - gray [yours]) of the rectifier bridge where the shorted diode occurred (you had a 50/50 chance)........

    This shorted diode was on the "-" side (another 50/50 chance) of the bridge, this shorted diode beings it was wired on the "-" terminal of the bridge then pulled the tach's signal to ground'ish.(Tach goes dead, signal wire is shorted to ground via shorted diode to ground)

    Either yellow or yellow-gray wire however should work, esp now that the shorted diode (bad rec) is removed...The tach's signal (derived from the charge winding AC pulses) should be the same on either yellow or yellow-gray.......

    Click image for larger version  Name:	Flash.jpg Views:	1 Size:	121.2 KB ID:	10693228
    Last edited by sam am I; January 3rd, 2019, 11:12 AM.


    • #3
      sam thank you very much for the explanation and diagram and time helped me a bunch


      • #4
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        Very welcome sir and glad it helped......