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Old 30-09-2018, 18:31   #1
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How to diagnose tachometer?

I have a 2000 Hunter 420- wonderful vessel, that I've had for four years. The hours on the engine are 820.

The tachometer seems to not be functioning. It reads zero with low rpm's, then 2500 with anything med-high rpms. Nothing in-between!

Any thoughts on where I begin with this?
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Old 01-10-2018, 05:38   #2
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Re: How to diagnose tachometer?

Tachs go south, sometimes. If it's a Faria tach, they'll rebuild it for not too much money, but you lose the hours.

Or you could replace whatever it is with either an Aetna or CruzPro digital tach (or others, maybe, including other analog tachs) depending on your cut-out size and sender.

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Old 20-12-2018, 12:25   #3
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Re: How to diagnose tachometer?

I have a 1989 Catalina 30 MKII with a Universal M25XP diesel. The tach is intermittent , showing either the correct RPM or reading zero. I deduce that the signal is not getting from the alternator/flywheel to the tach due to an intermittent bad connection.

Tracing the wire from the tach to the signal source and cleaning/tightening everything in-between should fix it, (in my junior electrician mind anyway).

My question is: how to test the signal wire output at the tach, using a multi-meter or some other circuit testing device?

(How many programmers does it take to change a light bulb? NONE. That's a hardware problem).

Thank you for any insights, as I am the pgmr mentioned above...
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Old 21-12-2018, 06:36   #4
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Re: How to diagnose tachometer?

Checking the wiring is a reasonable guess, but if you want to do this in a more structured way then start at the begginning and work to the end. The beggining in this case is the alternator. That is where the tach derives its signal. I would start with testing the alternator, or having it tested, then work my way up the wires testing continuity and cleaning connectors.

Very simply you can start by testing the feed for the tach coming off the alternator. If you are getting a variable signal there then it is likely the alternator or regulator. If so, since you arent a hardware guy , then take the alternator into an alternator shop (NOT to a machanic, who will just gouge you, but directly to an alternator/electric motor shop) to have it tested and repaired if necessary.

The tach itself failing is far less common than an alternator/regulator or wiring problem.

Do you have an internal or external regulator?
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Old 21-12-2018, 06:56   #5
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Re: How to diagnose tachometer?

Owning a “mature” boat, I would not trace the wire. It is too easy to miss something.

Assuming the issue happens every hour or so. Identify the correct post on the alternator and jump a wire direct to the tach. It need not be properly installed this is a test connection. Run the boat. If it still happens it is either the tach or alternator- NOW you have to spend money. My guess would be the alternator.

If the problem does not return, it is the wire you just solved the issue in one step, without spending a dime. Now REMOVE the bad wire and pull the new one.
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Old 21-12-2018, 06:58   #6
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Re: How to diagnose tachometer?

Some engines use a sender on the flywheel but most use a terminal on the alternator, usually labeled ‘W’. With the engine running, you should see 5-8 volts AC when you test it with your multimeter. If your tachometer is original, it’s nearly 30 years old and it wouldn’t surprise me if it needed replacing. However, the same is true for your alternator.

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Old 21-12-2018, 07:31   #7
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Re: How to diagnose tachometer?

If the tacho gets its signal from the alternator.... check alternator belt tension, a slipping belt is not uncommon, and therefore readings are low or zero.
One can buy very cheaply handheld digital tachometer, and then you can check and compare the readings. Installing a new sender on the flywheeel (and a new tacho from a third party) will fix all the above problems for many years to come.
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Old 21-12-2018, 07:43   #8
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Re: How to diagnose tachometer?

Troubleshooting Teleflex Tachometer Gauges ➥ https://www.jamestowndistributors.co...t.do?docId=837

Faria ➥ http://faria-instruments.com/site_ma...achometers.pdf
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Old 21-12-2018, 13:57   #9
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Lightbulb Re: How to diagnose tachometer?

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Old 21-12-2018, 15:10   #10
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Re: How to diagnose tachometer?

Quote:
Originally Posted by belizesailor View Post
Checking the wiring is a reasonable guess, but if you want to do this in a more structured way then start at the begginning and work to the end. The beggining in this case is the alternator. That is where the tach derives its signal. I would start with testing the alternator, or having it tested, then work my way up the wires testing continuity and cleaning connectors.

Very simply you can start by testing the feed for the tach coming off the alternator. If you are getting a variable signal there then it is likely the alternator or regulator. If so, since you arent a hardware guy , then take the alternator into an alternator shop (NOT to a machanic, who will just gouge you, but directly to an alternator/electric motor shop) to have it tested and repaired if necessary.

The tach itself failing is far less common than an alternator/regulator or wiring problem.

Do you have an internal or external regulator?

I thought this box, (pictured), mounted on the side of the galley counter, above the engine might be the regulator. On further inspection it appears to be a charger, perhaps that is one of its functions. I also have a definite battery charger mounted on the starboard side just behind the chart table. It charges when we are on shore power, it clearly has the switches and indicator lights of a pure battery charger. Perhaps the photo is the regulator which charges from the alternator, while the charger behind the chart table is for charging from shore power.
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Old 21-12-2018, 15:19   #11
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Re: How to diagnose tachometer?

That is a 20 amp charger in the picture which appears to be similar to those used by Catalina at the time.
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Old 21-12-2018, 16:05   #12
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Re: How to diagnose tachometer?

Quote:
Originally Posted by iyamwhatiyam View Post
I thought this box, (pictured), mounted on the side of the galley counter, above the engine might be the regulator. On further inspection it appears to be a charger, perhaps that is one of its functions. I also have a definite battery charger mounted on the starboard side just behind the chart table. It charges when we are on shore power, it clearly has the switches and indicator lights of a pure battery charger. Perhaps the photo is the regulator which charges from the alternator, while the charger behind the chart table is for charging from shore power.
Nope. Thats a charger not a regulator. Look at the INPUT specs printed on it...thats for shore power.

Do a little research on what regulators do and internal vs external regulators. They do not CHARGE from the alternator, they do what their name implies, they REGULATE (AKA control) the charge output of the alternator.

Internal regulators are, as the name implies, built into the regulator. Externals are...wait for it...external to the alternator. Externals are typically much "smarter" than internals (which are typically just basic automotive style regulators).

An external regulator is typically much smaller than a battery charger. For an example see the link to Balmar external regulators below. Note these regulators are only about 5-6" long and 2-3" wide.

http://www.balmar.net/multi-stage-regulators/

My first guest would be that youve got an internal regulator, but no way to know for sure without looking.
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Old 21-12-2018, 16:40   #13
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Re: How to diagnose tachometer?

does the engine have a TACH connection or is it from the alternator?
if its from the alternator...is it slipping under load..
I've seen ours do exactly what you're describing..
tighten the alternator belt..tach works fine..
of charge the batteries by other means before running the engine.


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Old 21-12-2018, 17:28   #14
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Re: How to diagnose tachometer?

Quote:
Originally Posted by belizesailor View Post

My first guest would be that youve got an internal regulator, but no way to know for sure without looking.

Boy do I look dumb after reading Don Casey on Charging Systems. I am not at the boat, but I have NEVER seen an external regulator anywhere. Heh, yup, that's a charger alright.
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Old 21-12-2018, 19:23   #15
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Re: How to diagnose tachometer?

Quote:
Originally Posted by belizesailor View Post
Nope. Thats a charger not a regulator. Look at the INPUT specs printed on it...thats for shore power.

Do a little research on what regulators do and internal vs external regulators. They do not CHARGE from the alternator, they do what their name implies, they REGULATE (AKA control) the charge output of the alternator.

Internal regulators are, as the name implies, built into the regulator. Externals are...wait for it...external to the alternator. Externals are typically much "smarter" than internals (which are typically just basic automotive style regulators).

An external regulator is typically much smaller than a battery charger. For an example see the link to Balmar external regulators below. Note these regulators are only about 5-6" long and 2-3" wide.

http://www.balmar.net/multi-stage-regulators/

My first guest would be that youve got an internal regulator, but no way to know for sure without looking.
Corrections:

"Internal regulators are, as the name implies, built into the regulator."

That should read "....into the alternator.".

"My first guest..." Should be "guess" obviously.
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