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Author Topic:   Dead Tachometer
rmart posted 09-28-2002 09:39 PM ET (US)   Profile for rmart   Send Email to rmart  
How do I know if my tachometer is dead and needs to be replaced or if something in the wiring or power supply is wrong?

Right now I get no reading on the tach but the light for this instrument comes on indicating there is power.

Clark Roberts posted 09-29-2002 06:49 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
check "sender" connection at tach and at rectifier... good luck
bdb posted 09-29-2002 06:57 AM ET (US)     Profile for bdb  Send Email to bdb     
Also check the rectifier itself. Quite common: rectifier dies, tach won't read.
jimh posted 09-29-2002 08:25 AM ET (US)     Profile for jimh  Send Email to jimh     
Connect an oscilloscope to the tachometer lead from the engine and verify there are pulses of approximately 14-volt peak and at a frequency equal to the number of stator poles times the crankcase speed in revolutions per minute.

Lacking an oscilloscope you can measure the pulse lead with an AC Voltmeter with respect to ground. You should indicate an AC voltage but it will be impossible for me to predict what reading you will get (as it depends on the characteristics of the engine and the meter).

rmart posted 09-29-2002 11:16 PM ET (US)     Profile for rmart  Send Email to rmart     
I am absolutely green to engine repair and electrical work. Is this type of repair beyond me? I have examined the wires and they appear to be in good condition and tight. Should I leave it at that and pay someone to fix my tach now? Or is this a repair I am capable of? Any suggestions for reading materials or manuals would be greatly appreciated.

I have an analog tach with the 3 light oil display. Tnanks for your input so far!

rkong posted 09-30-2002 04:13 AM ET (US)     Profile for rkong  Send Email to rkong     
Pick up a manual for your outboard and you'll be able to diagnose it yourself.

I knew zilch about engines a few weeks ago and picked up a manual. I was then able to conclude that my regulator was the problem (tach wasn't working). Replaced it and it worked fine after.

Also, if you notice you batteries die strangely and the regulator is hot when the engine is off and just sitting there, it's probably your regulator/rectifier... That was another sympton I had.

rmart posted 09-30-2002 02:03 PM ET (US)     Profile for rmart  Send Email to rmart     
I have a Clymer Shop Manual for my engine. But in reviewing this manual I have not seen any information on "regulators" "tachometers" or "rectifiers".

Am I missing something? Or should I get another manual? Thanks for your patience and assistance.

lhg posted 09-30-2002 02:26 PM ET (US)     Profile for lhg    
Try to first determine if the tach is bad. Put in an alternate tach, and see if it works. You can pick up one fairly cheaply. Or connect up your tach to a freinds engine, and see if it works.

If the tach is not bad, it's probably your rectifier on the engine. I'm betting on the rectifier.

rmart posted 09-30-2002 10:08 PM ET (US)     Profile for rmart  Send Email to rmart     
Does a "recitifier" go by any other name? I have scanned my Clymer engine manual index and cannot locate any reference to this engine rectifier that you reference. Any assistance in locating this would be greatly appreciated. Sorry for being so clueless when it comes to engines.
rkong posted 09-30-2002 10:27 PM ET (US)     Profile for rkong  Send Email to rkong     
Just curious what outboard you have? You can't find anything on trouble shooting your tachometer in your manual?
rmart posted 09-30-2002 11:08 PM ET (US)     Profile for rmart  Send Email to rmart     
1987 Yamaha 115....and I have a Clymer shop manual...
jimh posted 09-30-2002 11:51 PM ET (US)     Profile for jimh  Send Email to jimh     
For most outboard "mechanics", anything electrical is a mystery. That's why they're called "mechanics."

Coincidentally, I have a pair of 1987 Yamaha (70-HP) engines. Both of them experienced failure of their tachometers. In each case it was a failure of the stator winding which supplied the pulses to the tachometer (and the battery charging current).

It has been my experience that people who have a basic understanding of electricity and are familiar with simple test equipment can analyze and isolate the problems with the battery charging and tachometer circuitry. For people are not familiar with basic electronics and are not experienced with the use of simple test equipment, it will be impossible to describe the procedure in a forum such as this to the degree of detail needed to instruct someone on how to perform the diagnosis and repair.

If you are in the former group:
--check the stator (the "lighting coil')
--check the rectifier
--check connections to tachometer
--check the tachometer (on known-good engine)

jimh posted 09-30-2002 11:54 PM ET (US)     Profile for jimh  Send Email to jimh     
If your problem is the stator coil, the replacement coil will cost about $100-125 and require at least one hour of shop labor to replace ($75).

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