Tach test question

[CaptonZap]

I'll address this to DiverRay, since he works on these things, but solicit input from anybody that wants to chime in.
I have an inoperative tach, and have checked the alternator, which has three good coils, and would like to hone in on where the problem lies, without taking too many of the components apart. Since the tach has a plug that is accessible, it occurred to me that if one were to input a signal to the tach through the plug, you would know if the fault lay in the tach or the intermediate wiring.
What to use for the signal?
Would a signal generator fed into a stereo amp channel, with the speaker output wired to the tach, create a response in a good tach? 3000 Hertz is 3000 RPM in my book. Output voltage could be limited to 14 V, although, since the tach should read, even when the alternator coil is not putting out full rated voltage. i.e. at idle RPM's, and the voltage could be reduced, and a reading should still be available.
Any thoughts by you electrical wizards?

CZ

[DiverRay]

Tach runs off an "un-regulated" voltage source. A good signal generator at 3KHrz should give a signal. If you have the generator, you should not need the audio source. I'll have to look at the schematic to give you the correct pair for the signal.
I think you may find one of two things wrong, the grease that lubes the movement has gotten hard, or the movement itself has a broken part. That will cover about 95% of the tach problems, IMHO. Just remember, I have been proven wrong before, and I AM human, or close to it.

[TopCatGr58]

Tach runs off an "un-regulated" voltage source.

Hey Zap and Ray,

The tach wire is essentially unregulated.....BUT it does have a DIODE in line with it so that it allows a 1 direction PULSE signal vs. an AC signal.

Folks have found their DIODE can go bad leading to loss of signal and dead tach. You should be able to access the white wire in the ALT connector behind the fuse block, and put a diode in line with the test/jumper wire and then run it to the tach wire as a way to test the tach with the bike. IF it then works....then you probably have a dead diode, if not a damaged signal wire.

T.C.

[CaptonZap]

Thanks for the input TC.
The way I read my schematic is that the diode is in the wire that clamps the head light relay, and the tach is fed off of one of the other white wires.
Anybody with a diagram for an 80 G that show something different?

CZ

[TopCatGr58]

Hey Zap,

What's that phrase, best have folks think you're a fool, than to open your mouth and prove it? Yep, BRAIN FART....diode IS for the headlight relay..DOH ...RAW feed from other leg of ALT going directly to the tach!

I NOW remember when I was figuring out my Race Alt MOD that just taking a tap off of one of the legs of that ALT worked just fine to feed the tach and have it read correctly since I kept the # of RPMs of the Race ALT equal to the crank RPMS, and it had the same # of poles as well, so same # of pulses.

However, I will add that after a while my tach did stop working. My race alt put out almost twice as much power as the XS11's OEM, and so with that much amperage I could have burned up something in the Tach.? That's another reason why I went with the aftermarket gauge cluster with speedo/tach combo running off of my ignition coils as trigger.

T.C.

[CaptonZap]

Tach runs off an "un-regulated" voltage source. A good signal generator at 3KHrz should give a signal. If you have the generator, you should not need the audio source. I'll have to look at the schematic to give you the correct pair for the signal.
I think you may find one of two things wrong, the grease that lubes the movement has gotten hard, or the movement itself has a broken part. That will cover about 95% of the tach problems, IMHO. Just remember, I have been proven wrong before, and I AM human, or close to it.

Good info Ray.
According to this schematic,
http://https://lh3.googleusercontent...2/XS11G_US.jpg,
it looks as though the brown feeds 12 V, black is ground, and the white is signal.
So a signal from the generator to the white, with it's ground to a common ground with the 12 V supply, both grounds to the black should emulate the bike wiring? And I can test the tach on the bench.

CZ

[3Phase]

Good info Ray.
According to this schematic,
(elided)
it looks as though the brown feeds 12 V, black is ground, and the white is signal.
So a signal from the generator to the white, with it's ground to a common ground with the 12 V supply, both grounds to the black should emulate the bike wiring? And I can test the tach on the bench.

CZ

Bingo, Cap.

If it works, tap it gently. Hold it in your hand while it's working, then rotate it around its axis to see if the internal bearing contacts in the galvanometer are worn or if the hair springs are broken.


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Over the years, people have saved it in JPG and PNG formats with 32 or 24 bit color so they're triple the size or more than they're supposed to be and a lot of them are blurry too. It makes me smile.

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