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Old 01-04-2011, 11:36   #1
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RPM meter not working

Engine is running fine, but the RPM meter is not registering anything. I traced the sensor wire and it seems fine, power is there and other wires seemed to all be properly attached. Is it at all unusual for the meters themselves to go bad?
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Old 01-04-2011, 11:43   #2
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Re: RPM meter not working

What is the engine and what kind of tach?
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Old 01-04-2011, 12:50   #3
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Re: RPM meter not working

Could be a bad sending unit; I would look there first.
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Old 01-04-2011, 13:34   #4
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Re: RPM meter not working

I had to replace a Yanmar RPN meter about 30 days ago. Went through the exercise of checking EVERYTHING else first, but it was the doggone meter that fixed it.
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Old 01-04-2011, 13:47   #5
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Re: RPM meter not working

If memory serves, some tachometers run off the alternator. Were it me, I would try replacing the meter and then see. A bit more info might be helpful.
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Old 01-04-2011, 14:06   #6
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Re: RPM meter not working

...and, if the batteries are fully charged, the alternator will stop charging, so no signal to drive the tachometer.
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Old 01-04-2011, 14:07   #7
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Re: RPM meter not working

Really check the power and ground connections on the tach carefully. I have had this go bad and cleaned all the connectors, worked fine after that. One of the intermittent connections was the feed power coming from the water temp gauge.
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Old 01-04-2011, 14:08   #8
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Re: RPM meter not working

Also, if it's a flywheel reader, they require a certain distance/gap from the flywheel. You might check, but it would be hard for it to unscrew with wires attached.
The yanmars are preset, they screw down to the shoulder.
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Old 01-04-2011, 14:20   #9
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Re: RPM meter not working

Quote:
Originally Posted by steve_hendry View Post
...and, if the batteries are fully charged, the alternator will stop charging, so no signal to drive the tachometer.

That is just not the case. Our tach and many, many others run off the alternator and it would be very counter productive if they stopped working when the battery is charged. It is actually connected to the AC output of the alternator. Chuck
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Old 01-04-2011, 14:20   #10
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Re: RPM meter not working

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...and, if the batteries are fully charged, the alternator will stop charging, so no signal to drive the tachometer.
Uh, sorry. This is simply wrong. Alternator driven tachs (actually the power comes off the rectifier) are pulse driven (e.g., a 12 pole alternator will have the tach set at 6 pulses since the alternator runs at twice engine speed typically) and operate regardless of the battery state of charge.
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Old 01-04-2011, 16:09   #11
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My RPM meter started sporadicly working and not working. It turned out to be the connection at the sender. Once I cleaned it and "pinched" the fitting it's worked perfectly.
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Old 01-04-2011, 17:58   #12
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Re: RPM meter not working

Quote:
Originally Posted by Mardav View Post
Uh, sorry. This is simply wrong. Alternator driven tachs (actually the power comes off the rectifier) are pulse driven (e.g., a 12 pole alternator will have the tach set at 6 pulses since the alternator runs at twice engine speed typically) and operate regardless of the battery state of charge.
However, if you have alternate charging sources, say solar panels, they can indeed raise the system voltage to the point that the regulator switches the field supply to the alternator completely off, and the tacho stops working.

Happens all the time on our boat... 240 watts of solar, 4xT-105, Balmar alternator and Balmar AR-4 regulator, Nanni tacho.

Cheers,

Jim
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