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Dennis.Kirby(at)kirtland.
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 Posted: Wed Dec 22, 2010 2:41 pm Post subject: 912 Tach Malfunction |
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Fellow 912 Kolbers –
Today, when I went flying, I noticed a problem with the tachometer on my Mark-III. Am hoping the collective wisdom of our 912 folks can help me pinpoint the problem.
The tach needle was jumping around erratically. It was mostly pointing to the correct RPM, but would often jump up to around 6000, then eventually settle back down to the actual RPM. This of course happening while the engine speed stays constant. Was doing it continuously throughout the flight.
The Rotax tachometer is electronic. I suspect a bad ground somewhere in the tachometer circuit, which will be easy to troubleshoot next time I’m at the airplane. Anybody else agree?
Many thanks –
Dennis Kirby
Mark-III “Magic Bike” in
Sandia Park, NM
[quote][b]
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Dana
Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA
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| Posted: Wed Dec 22, 2010 4:39 pm Post subject: 912 Tach Malfunction |
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At 05:38 PM 12/22/2010, Kirby, Dennis Civ USAF AFMC AFNWC/EN wrote:
| Quote: | | ... The tach needle was jumping around... I suspect a bad ground somewhere... |
I suspect a bad connection _somewhere_, not necessarily a ground. The tach measures frequency, and an interruption anywhere could overlay another frequency onto the tach signal.
-Dana
--
The most valuable function performed by the federal government is entertainment.
[quote][b]
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Wed Dec 22, 2010 7:05 pm Post subject: 912 Tach Malfunction |
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Dennis, The UMA tach I use with my 582 sometimes does this when it's too cold. I just assume it's shivering. Once it warms up it stops.
Rick Girard
On Wed, Dec 22, 2010 at 4:38 PM, Kirby, Dennis Civ USAF AFMC AFNWC/EN <Dennis.Kirby(at)kirtland.af.mil (Dennis.Kirby(at)kirtland.af.mil)> wrote:
| Quote: |
Fellow 912 Kolbers –
Today, when I went flying, I noticed a problem with the tachometer on my Mark-III. Am hoping the collective wisdom of our 912 folks can help me pinpoint the problem.
The tach needle was jumping around erratically. It was mostly pointing to the correct RPM, but would often jump up to around 6000, then eventually settle back down to the actual RPM. This of course happening while the engine speed stays constant. Was doing it continuously throughout the flight.
The Rotax tachometer is electronic. I suspect a bad ground somewhere in the tachometer circuit, which will be easy to troubleshoot next time I’m at the airplane. Anybody else agree?
Many thanks –
Dennis Kirby
Mark-III “Magic Bike” in
Sandia Park, NM
| Quote: |
_blank">www.aeroelectric.com
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get="_blank">http://www.matronics.com/Navigator?Kolb-List
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Zulu Delta
Kolb Mk IIIC
582 Gray head
4.00 C gearbox
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Thanks, Homer GBYM
It is not bigotry to be certain we are right; but it is bigotry to be unable to imagine how we might possibly have gone wrong.
- G.K. Chesterton
[quote][b]
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mdnanwelch7(at)hotmail.co
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| Posted: Wed Dec 22, 2010 8:13 pm Post subject: 912 Tach Malfunction |
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The Rotax tachometer is electronic. I suspect a bad ground somewhere in the tachometer
circuit, which will be easy to troubleshoot next time I’m at the airplane. Anybody else agree?
Many thanks –
Dennis Kirby
Dennis,
First thing you want to do is verify all the wire connections are taken apart and retightened.
(the hot lead, the ground, and the signal lead) If that doesn't solve the problem, then here's
my thoughts...
Your tach is a simple frequency counter. Since yours is electronic, 99.9% of its innards are
unadjustable (capacitors, resistors, transistors, a couple of integrated circuits, and a few diodes).
Either they work or they don't!! Except for one thing; the potentiometer, which that COULD
create such a symptom is if the internal potentiometer is a little corroded, it would interpret a
really bad frequency, thereby making the needle swing wildly.
If you take your tachometer apart, there should be at least one potentiometer (known
as a 'pot'). I'd bet if you could spray it with electronics parts cleaner, it would help. You
ought make sure you don't screw up it's calibration, though. That potentiometer is what the
tach uses for calibration. I think it is the only thing inside that's adjustable, and possibly
corrodible.
If you plan on trying to fix it yourself, maybe you could try this; Start the engine, let it warm
up. See what rpms the tach says. Then remove the tach, take off the housing, look for the
pot. Once you find the pot, note where it is presently set at!! Spray a little parts cleaner on
the pot. With your tiny screwdriver, twist a little left and right a few times. Spray it again,
then reset it close to where it started at. Now hook it back up temporarily to your engine with
the housing still off.
Start your engine, and turn the pot until the tach says the exact same rpm it said before you took
it apart. Once you're happy that you have reset it correctly, put it back together, and re-install it.
This is just a guess....
Mike Welch
[quote][b]
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by0ung(at)brigham.net
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| Posted: Thu Dec 23, 2010 11:30 am Post subject: 912 Tach Malfunction |
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The tach needle was jumping around erratically. It was mostly pointing to the correct RPM, but would often jump up to around 6000, then eventually settle back down to the actual RPM. This of course happening while the engine speed stays constant. Was doing it continuously throughout the flight.
Dennis Kirby
Mark-III “Magic Bike” in
Sandia Park, NM[quote]>>>>>>>>>>>>>>>>>>>>> i think you are thinking correctly.. loose connection.. i am using the EIS and have not had any problems.
boyd do not archive [b]
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captainron1(at)cox.net
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| Posted: Sat Dec 25, 2010 10:48 am Post subject: 912 Tach Malfunction |
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I think that ought to fix it if it's not a simple wire connection. I would add that ACF-50 or Corrosion-X would be the magic potion. ACF-50 or corrosion-X are truly magical. I use both in my airplane cars and motorcycle and any other place that has electrical stuff. These potions are simply amazing. I'd use them on my joints if I could figure out how.
A caution though, do not use them anywhere near the wheels. I had some corrosion discoloring on my car wheels and thought I'd use Corrosion-X to get rid of it. The stuff is so powerfully dielectric that it migrated to the studs and the frigging wheels loosened up. It may be funny but it ain't if you are on your way to Tucson and you get vibration to chatter your teeth loose.
So don't use that stuff near bolts unless they are cotter'd or safety wired, especially on a vibrating airplane.
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Dennis.Kirby(at)kirtland.
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| Posted: Wed Dec 29, 2010 7:33 am Post subject: 912 Tach Malfunction |
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<< The tach needle was jumping around erratically on my Mark-3 >>
Kolb Friends –
Here’s a quick update on my erratic tach situation: It turned out to be a simple matter of corrosion on the tach terminals. Easy fix – I just pulled off each of the three electrical terminals on the back of the tachometer, then re-attached them to achieve positive contact again. On close inspection of the terminal posts, I could see a slight surface coating of corrosion – probably leftover from my salt flats landing in 2006. (ugh)
Flew the airplane, and the tach worked just fine. Am glad I did not have to open up to instrument to investigate the innards.
My thanks to Dana, Rick G, Mike W, Boyd and Cap’n Ron for your various ideas and thoughts. It’s what makes this List so valuable.
Dennis K.
New Mexico
[quote][b]
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