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Author Topic:   Diagnosis of Engine Tachometer Problem
grosseile88 posted 12-27-2014 12:56 PM ET (US)   Profile for grosseile88   Send Email to grosseile88  
The tachometer died on my 1985 Evinrude 70-HP. The [tachometer is] not original but [is a used tachometer that was] purchased a few years back. The tachometer seemed to die a slow death. The tachometer would work intermittently at higher engine speed, but now is completely dead. Before I just replace it, is there something else I should check? The wiring to tachometer is not corroded or loose. The tachometer lights up when the NAVIGATION LIGHT are ON, though that does not really mean anything. I saw some other posts that say to check the rectifier. Have not checked the rectifier, but kind of eliminated rectifier problem since I been running the boat all season with a dead tachometer and not had any charging malfunction. I only charge my battery once at the beginning of the season. Is there some other sending unit the tachmeter gets it signal from that I should check?

Any thoughts would be appreciated before I replace the tachometer. Thanks!


jimh posted 12-28-2014 09:26 AM ET (US)     Profile for jimh  Send Email to jimh     
Before any further diagnositic tests are made, I recommend you perform the following procedure:

--locate the tachometer calibration control. The calibration control is usually on the rear face of the tachometer and appears as a small rotary control with a slot;

--note the present orientation of the calibration control. Some sort of pointer indicator usually points at a calibration scale with numbered digits;

--locate a suitable small screwdriver that will fit into the slot of calibration control;

--carefully insert the tip of the small screwdriver into the slot of the calibration control, and rotate the calibration control back and forth through its range of motion at least ten times; this will wipe the contacts of the control circuit and perhaps remove any oxidation or other corrosion on the contacts;

--return the calibration control to its original position

This procedure often restores operation to marine outboard engine tachometers. Report back with the status of the tachometer after performing this test.

Diagnostic advice on causes and remedies for outboard engine tachometer problems is offered in:

grosseile88 posted 12-29-2014 02:24 PM ET (US)     Profile for grosseile88  Send Email to grosseile88     

I know exactly were that control is, I will give that a shot and report back.

Thanks for the tip!!!

jimh posted 12-29-2014 07:42 PM ET (US)     Profile for jimh  Send Email to jimh     
When you rotate the calibration control through its range, be careful that you limit your force on the control to the minimum necessary--you don't want to force the control farther than it wants to go. One fellow reported back that after he tried this procedure there was no detent left; I am afraid he might have overdone the force used and wrecked the detent.
grosseile88 posted 01-06-2015 10:13 AM ET (US)     Profile for grosseile88  Send Email to grosseile88     

I will try to get under the boat cover this weekend after the artic blasts passes trough Atlanta and see if your solution fixes the problem.


grosseile88 posted 04-25-2015 09:57 AM ET (US)     Profile for grosseile88  Send Email to grosseile88     
Finally got the boat dusted off and fired up for the spring. I tried the suggestion of moving the pole setting pin around several times. Tach is still dead. I bought the tach used a few years back so no telling how old it is so I just ordered a new one. It seems to be charging correctly and the rectifier looks good to the naked eyes. However it is original so no telling. If the new tach does not fix the problem I will test rectifier and replace if neccessary. Thanks for all the tips I will report back.
jimh posted 04-25-2015 12:38 PM ET (US)     Profile for jimh  Send Email to jimh     
When power is applied to the tachometer, does the dial pointer of the tachometer change position? Have you checked to see if there is 12-Volts being supplied to the gauge?
grosseile88 posted 04-29-2015 01:58 PM ET (US)     Profile for grosseile88  Send Email to grosseile88     
When power is applied to tach (key turned on) the dial needle does not change. I seem to remember that when it was working it would move or jump a bit when ignition turned on?? Would this mean I have a charging issue or a tack issue? I ordered a new tach and rectifier to be safe. I was going to start by swapping out the rectifier to see if that solves tach issue and if it does return the tach.
jimh posted 04-29-2015 03:16 PM ET (US)     Profile for jimh  Send Email to jimh     
I don't see any issue in any of this. I see electrical problems. Issues arise only when one human does not agree with another human about some important topic of wide interest. Humans cannot have issues with non-living, non-speaking electrical devices.

If there is no movement of the dial pointer at all from its resting position without power to its position with power but the engine not running, that indicates to me there is something wrong, either with the power to the device or something inside the device.

jimh posted 04-29-2015 03:18 PM ET (US)     Profile for jimh  Send Email to jimh     
Have you actually measured the presence of 12-Volts on the I-terminal of the tachometer?
grosseile88 posted 04-30-2015 07:45 AM ET (US)     Profile for grosseile88  Send Email to grosseile88     
Back in town so I tested to see if there was power going to tach and there was not. The tach lights up but I have that on the nav light circuit. So from here does this point to an instrument issue or someplace else? Because I was bored I started poking around the terminal block on starboard side of engine that the rectifier leads go to. With the ignition still on the #7,6,5 slots did not light up but the 1,2,3 slots did light up. This probably was an exercise in futility but thought I would share incase it did point to a rectifier problem or other.

Thanks again for the help!

grosseile88 posted 05-04-2015 12:34 PM ET (US)     Profile for grosseile88  Send Email to grosseile88     

Turned out the tach was DOA. Replaced tach and it works perfectly. Replaced rectifier too since I already had a new one and one on the motor was original. Everything is working like a charm!

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