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Author Topic:   Intermittent Tachometer, 1992 Johnson 100-HP
sail16 posted 09-30-2005 09:34 PM ET (US)   Profile for sail16   Send Email to sail16  
Engine: 1992 Johnson 100 GT

Symptoms: Tach will register properly for the first few minutes after starting, then will drop to zero. Battery voltage never seems to rise about 12.4v and often seems to run low.

Actions so far: Checked stator for ground / short-- seems fine. Replaced tach-- same problem.


kingfish posted 09-30-2005 11:20 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Sounds like the rectifier to me - I had similar symptoms with my 1991 Evinrude 225, replaced the rectifier, and symptoms went away. There are tests a mechanic (or you, armed with service manual and multi-meter) can run to test it.


Joe Kriz posted 09-30-2005 11:53 PM ET (US)     Profile for Joe Kriz  Send Email to Joe Kriz     
I had the same problem as you and kingfish.

Replaced the rectifier and all was OK...

high sierra posted 10-01-2005 12:43 AM ET (US)     Profile for high sierra  Send Email to high sierra     
Sail16 , there are 3 diodes in a rectifier. One has failed and now the alternating current is flowing both ways. The rectifier is shot. High sierra
Peter posted 10-01-2005 07:46 AM ET (US)     Profile for Peter  Send Email to Peter     
Another vote for the voltage rectifier.
Robob2003 posted 10-01-2005 09:51 AM ET (US)     Profile for Robob2003  Send Email to Robob2003     
See my post "OMC tach problem."

It's a simple test with an ohmmeter.

Bob on Tampa Bay

jimh posted 10-04-2005 10:53 PM ET (US)     Profile for jimh  Send Email to jimh     
The number of diodes in a rectifier is highly variable.

References to other articles should include Uniform Reference Indicators.

tn70 posted 05-15-2006 05:29 PM ET (US)     Profile for tn70  Send Email to tn70     
[I] have a similar prob[lem] with old [E]vinrude 70hp. [T]he tach[ometer] now does not work at ALL. It reads 5,000 all the time; needle does not move at all. [L]ast year, it would read sometimes, but very erratic.
jimh posted 05-15-2006 10:07 PM ET (US)     Profile for jimh  Send Email to jimh     
Electronic circuits are affected by heat. This often causes intermittent operation as an engine warms up.
SpeedBump posted 05-16-2006 08:00 PM ET (US)     Profile for SpeedBump  Send Email to SpeedBump     
I had a similar problem with my Nissan tach last season. Intermittent reading, mostly too high, but didn't have a low voltage reading.

Several suggestions on the forum included cleaning the contacts. This was the cheapest of all the proposed fixes so I purchased an aerosol can of contact cleaner at a local Radio Shack for $9.00, sprayed inside the tach and moved the cylinder setting knob back and forth a few times, reset the engine cylinder setting on the tack to the correct setting and bingo the problem was gone. I lucked out on that one as a new Nissan tach costs about $180.

jimh posted 05-16-2006 11:14 PM ET (US)     Profile for jimh  Send Email to jimh     
I have seen that same situation on a Mercury tachometer. Just rocking the calibration switch back and forth several times restored the contacts. I would not spray contact cleaner into the interior of the tachometer gauge. It might cause more problems than it fixes. Some cleaner sprays are harmful to some plastics. Try just moving the switch back and forth before resorting to the cleaner spray.

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