Tachometer Quit working JD 4400 tractor

[ohiogar]

Am in the process of restoring a 1998 JD 4400 Tractor with around 50 total hours on it from new. I have about 3 hours run time on it myself.
The tachometer worked fine and just quit all of a sudden. The hour meter works fine.
ALL of the factory safety's are functional. This is a pre computer machine.
I believe that the tach works off of a pulse from the alternator. A Trusted auto electric motor friend
tested and said the alternator is just fine. I even tried with a second used alternator.
I have traced all of the wiring and it also seems fine.
ALL of the relays have been switched around with extra's and have no effect on system.
I am clueless here. Any Ideas appreciated.
Regards from Ohio
gary

 

[Roadworthy]

Is there any way to test the tachometer itself, that is a substitute input to see if it reads?

 

[ohiogar]

I really do not know
I have read that the hour meter works off of the power supplied to the tachometer

 

[Roadworthy]

If there is no mechanical cable driving the tach it probably does feed off the alternator - counts pulses or something - not sure. Are your hour meter and tachometer both in the same unit or are they two separate instruments? That can work both ways. Unless it's a broken wire somewhere, unless you are familiar with working on instrumentation you should send the unit out for repair.

 

[ptsg]

Try wiggle the plug at the back of the dash. Or pull it out and check for corrosion on the pins. Sometimes it's all it takes.

 

[ohiogar]

Thanks I have done that many times. I have been over under inside and out and it will not work. BUT the hour meter works which is confusing
It is a new aftermarket dash cluster. Under advisement it just felt right to put
a new unit on a tractor with so many obvious signs of low hours.

 

[Agvg]

Is there any way to test the tachometer itself, that is a substitute input to see if it reads?

A signal generator could be used to make the pulses.

 

[ohiogar]

I have no knowledge of a signal generator. will research it.
I believe there is a pole on the alterntor that supplies that pulse.
How would one test that?
Thank You

 

[Williy]

You can get a meter from amaxon.com
You don't need the high dollar one just
get a cheap one for the price of the high
dollar one's u can get 4 or 5 cheapies!

willy

 

[rScotty]

It seems too simple, but doesn't the shop manual have a schematic?
BTW, does the JD4400/Yanmar engine clock measure "key-on" hours or engine RPM converted to hours? There doesn't seem to be any rule on this.

 

[ohiogar]

It must be the engine on hours
It does not increase with key on only

 

[ohiogar]

You can get a meter from amaxon.com
You don't need the high dollar one just
get a cheap one for the price of the high
dollar one's u can get 4 or 5 cheapies!

willy

zSince I really do not know what I am looking for would you be so kind as to give me a link to an amazon signal generator for sale
regards gary

 

[rScotty]

You can test the alternator connection with most any basic Volt/ohmmeter that has a setting for frequency.Both of my hand-held Fluke VOMs will not only tell if there is a signal - and all about it - but will also tell you the frequency.

That will give you the specifications of the signal that would need to be generated and will also confirm that the alternator is generating a signal.

I'd do that before investing in a signal generator.
You may already have a signal generator built right into the alternator - or somewhere else on the tractor.

Either you have a signal and the tach is fine, or you don't have a signal and no tach will ever work. Whatever the case, it makes sense to check if the tractor is putting out a signal to the gauge before buying a piece of test equipment to generate one of our own.

If you could attach a high resolution photo of the cable ends and the place on the tach where the cable attaches we might know a little more.
rScotty

 

[ohiogar]

Well in my original post an auto electric guy i have known for many years
says the alternator is doing whatever it is supposed to

 

[rScotty]

Well in my original post an auto electric guy i have known for many years
says the alternator is doing whatever it is supposed to.

I'm sure he is right. But does he even know that your alternator is one that has a special connector out for a pulse to run the tachometer? Did he look for that?

You might want to ask him that because maybe I'm just wrong - or more likely just way out of date. After all, it's been more than a few decades since I had my shop. But I've tested a lot of alternators, and I would usually usually just test them for output. I don't believe I have ever looked for some sort of special tach output from the AC side of the output coils. Generally I just look for charge voltage, voltage regulation & rectification, and at total amps. If they pass that, I called them good to go.

rScotty

 

[ohiogar]

Really Good Thought Scotty
He is an older guy that pretty much has his
guy fix stuff anymore but he tested this himself and I am sure I told him the tach runs off of the alternator and he said it was fine.
Us Old Folks Ha ha

 

[Century3040]

I'm sure he is right. But does he even know that your alternator is one that has a special connector out for a pulse to run the tachometer? Did he look for that?

You might want to ask him that because maybe I'm just wrong - or more likely just way out of date. After all, it's been more than a few decades since I had my shop. But I've tested a lot of alternators, and I would usually usually just test them for output. I don't believe I have ever looked for some sort of special tach output from the AC side of the output coils. Generally I just look for charge voltage, voltage regulation & rectification, and at total amps. If they pass that, I called them good to go.

rScotty

Would that affect the fuel gage, hour meter, and the temperature gage as well as the tachometer? Those 4 items are not working on my tractor, I was thinking a microprocessor in the dash???

 

[ohiogar]

Well the 1999's did not have a computer so no microprocesser.
I was told the tach and hour meter on mine both run off of the alternator pulse. BUT my hour meter works while the tach does not.
4000's deere fuel guages go bad a lot. ususlly the tank sender.
On cars the temp sending unit in the block is usually the culprit.Cannot help with newer machines.
Good Wrenching

 

[DieselBound]

IF alternator is ruled out (and it IS the driver of the tach) then that leaves:

1. Wiring - would have to check output at tach side connection point of wire/harness;
2. Tach - you said new dash; does this also mean new tach? (unproven equipment- possible DOA).

 

[ohiogar]

Well i have checked the continuity of the alt wire.
I am leaning toward the pulse thingy in the alternator. When it gets cold
i will head back in to have it checked
I suppose the new instrument cluster could be faulty but all other functions seem to work fine.