Tachometer not working

[cluseau]

I have a 1975 Evinrude 70 HP outboard and I cannot get the tach to work. This is the second tach that I have had on this boat and the first one never worked either. I fed it a square wave signal from a signal generator and it worked fine. This one is a brand new (NOS) OMC digital tach and it doesn't work either. It is set to 6 poles which per the installation instructions is correct for my outboard. I did a continuity check of the grey tach wire from the tach back to the engine terminal block and it is fine. There it meets up the yellow / grey wires coming out of the stator, just like the wiring diagram in the factory shop manual shows. The tach indicates 000 rpm so its 12 volt power wire and ground are OK. Charging is also OK, I am getting 13.5 volts or better when the engine is running. I am ready to throw both tachs in the lake along with the factory shop manual. Any ideas? Any help is appreciated!

 

[F_R]

Re: Tachometer not working

Sounds like you know what you are doing. That's the first time I've heard somebody say they used a square wave signal generator on one. (??)

My suggestion is to test ALL 4 diodes in the rectifier. Forward and reverse test on each. That is 8 tests in all. It is a full wave bridge rectifier, if you know what that means.

 

[Dabbler_E]

Re: Tachometer not working

If the tach is functional and hooked up correctly, motor is running, and you have connectivity to the motor, then the problem is very likely the rectifier, as F R indicates.

 

[SparkieBoat]

Re: Tachometer not working

funny I have had a rash of bad rectifiers lately..maybe its a bad moon for them or something

 

[cluseau]

Re: Tachometer not working

Thanks to all of you for your help. I checked the rectifier today and it has some open diodes. The funny thing is that I have a complete spare ignition system that I purchased on e-bay and when I checked the associated rectifier it too has some open diodes. These things must have a high failure rate like SparkieBoat has found. I may substitute a radio shack full wave bridge rectifier that I found in my parts box. It has a 25 amp capacity and a 50 PIV rating. It should be much more than adequate for my 6 amp system.

What threw me off is that my system does charge. I guess you can have a couple of diodes OOS and still have adequate charging capability. That is why I didn't suspect a bad diode.

 

[F_R]

Re: Tachometer not working

That Radio Shack bridge is probably better than the OEM one. Sure as hang a lot cheaper.

 

[SparkieBoat]

Re: Tachometer not working

what?? there is an alternative to the $200+++ OEM regulators????? If I can get something from radio shack that will work better for cheaper..someone please post how to do this...Thanks Sparkie

 

[Leglav8s10]

Re: Tachometer not working

I'm running into a similar problem in my boat. Sometimes the tach reads properly, and sometimes it reads way high. The voltmeter reads between 15 and 16v when running over 2000rpms. Would this be a regulator/rectifier combo or just one or the other? (sorry for the thread hijack) I have a 94 Johnson 120 v4 Looper.

 

[SparkieBoat]

Re: Tachometer not working

it looks like we both kinda thread hijacked...you really should post a new thread so we can deal with your specific situation. But I will tell you to go here and find your rectifier and then download the install sheet which tells you how to test it. you will need a DVA adapter and a multi meter..2 tools you will use again if you continue to own outboard motors or have friends who do. The DVA adapter can also be used to test power packs and stators..very handy and well worth the $35...google it for best price

 

[SparkieBoat]

Re: Tachometer not working

forgot to post link...here it is
http://www.cdielectronics.com/Products.aspx?Criteria=1H
you will need to find your part number first.