Tach is not working

[MichaelMullis]

How would a Tach be checked. Can it be checked with a voltmeter, ampmeter, ohmmeter? I need to find out why mine is not working. I just got this boat yesterday so I have not checked out fully, but know that the tach was not working when I did test run. Prev. owner said that it had not worked since he bought 1.5 years ago.This is a 1998 70hp Johnson 4-stroke.<br />thanks<br />michael

 

[eurolarva]

Re: Tach is not working

I would check the rectifier on your motor. Most tachs are run off of these. You can test the rectifier by connecting a volt meter to your battery and then running the motor. If voltage does not increase chances are your rectifier is toast.

 

[kesso]

Re: Tach is not working

Does the battery look like it has been in the boat for a while? If it does, then it is probably being adequately charged and your rectifier assembly is most probably good; however, I would do eurolarva's test if you have the appropriate test equipment at hand.<br /><br />I would suggest some other simple checks:<br /><br />1. 12VDC connected to the tacho<br />2. Ground connected to the tacho<br />3. Sender wire conected to the tacho<br />4. Confirm correct tacho alternator pole setting

 

[Moody Blue]

Re: Tach is not working

Start at the tach and work back to the motor. You will need a digital (or analog) multimeter. Your tach will have 3 terminals 12VDC (probably purple wire), GND (black wire), SIGNAL (probably grey wire) and a light connection. Start motor and measure voltage at battery. If 12V or less then rectifier is shot and tach will not work. If 13V or more then rectifier is good and problem is elsewhere. Shut off motor.<br />1) With key in RUN position and motor off, check for 12VDC at 12V terminal on the tach.<br />2) Using an ohmmeter, check for good GND connection on GND terminal on tach.<br />Correct any issues above before continuing.<br />Start engine.<br />3) Using AC mode on multimeter, check for voltage on SIGNAL terminal on tach. Vary motor RPM and check that voltage varies as well.<br />If you have all the above and the tach does not work then it is toast.

 

[MichaelMullis]

Re: Tach is not working

Thanks for info guys, I checked tach. last night and here is what I got.<br />1) with motor off checked batt had 12.8VDC<br /> cranked motor, had 14.3 VDC.<br />2)At Tach with key on but motor off. had 12VDC on purple wire.Had good ground. Had 12VDC at light when NAV. lights were on, and had light.<br />3) Cranked motor to check output of sending unit(Grey Wire). Had 1.5 Vac at idle, 2.3 at about 1/4 thottle, and about 3.8 at about 1/2 throttle. These may be Millivolts I left my notes at home.<br />What should these be around? The Tach was not moving as I increased RPM.<br />I think it is tach time, What do you guys think.<br />Thanks<br />Michael

 

[kesso]

Re: Tach is not working

Does this tacho have a pole selection switch on the back?

 

[MichaelMullis]

Re: Tach is not working

Hello Kesso, Yes it does. I beleive it is set on 4. It has 1-6 positions. This is a 1998 70hp 4-stroke Johnson, Electronic fuel injection. <br />Thanks for all the help so far Guys. It's really good to have a site to get info when you need it.<br />Michael

 

[gaugeguy]

Re: Tach is not working

You want to see between 3 and 4 volts AC at idle and between 5-7 volts AC around 2000 RPM measured at the S terminal.

 

[MichaelMullis]

Re: Tach is not working

gaugeguy, I rechecked outputs over the weekend. When I cranked motor, Voltage on battery went from 12.83 to 14.48. Output on tach. sending eire at idle was between 2-3 volts, at about 1/2 throttle was about 5.3 volts. I do not have a portable tach so I do not know what rpm I was turning. I will get a portable tach this week and will check again.<br />Thanks<br />Michael

 

[kesso]

Re: Tach is not working

What Brand/Manufacturer is the subject tacho?<br /><br />I believe your altenator has 12 poles. Generally (stress generally) you have to set the pole selector switch on the back to 6P. You said yours was set to position 4; does position 4 equate to 6P or does position 6 or another position equate to 6P. <br /><br />Are there any markings for the pole selector switch?<br /><br />Does the tacho needle zero-out or make any subtle movement when the key is switched to 'on'?

 

[gaugeguy]

Re: Tach is not working

If you have those voltages on your B+ and tach signal inputs, it sounds like the tach is indeed junk.<br /><br />Even if the tach were set in the wrong "p" position, it would still read, it would just be inaccurate.

 

[MichaelMullis]

Re: Tach is not working

Kesso, the Tach is a Faria, or maybe Fania, the writing is in script and I am not sure of spelling. The only markings on the back are the setting positions 1,2,3,4,5,6. All of the terminals are marked but nothing else that I can see.<br />Thanks <br />Michael

 

[kesso]

Re: Tach is not working

Try the manufacturers information:<br /><br /> http://www.faria-instruments.com/index-new.html