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mark.bitterlich(at)navy.m
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 Posted: Wed Nov 01, 2017 3:42 pm Post subject: [Non-DoD Source] Yak55M Tachometer |
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The tach in the Russian airplanes uses a 3 phase AC system. The actions of your tach indicator point to one of the phases being intermittent or missing entirely. The typical place this fails is in the solder joint of the tach generator cannon plug itself. Not always mind you, but it is a good place to start looking. Lots of ways to check this. You can start by checking the wires with an ohm-meter by removing both the tach gen and tach indicator plugs and checking continuity.
If the wiring checks good... and you are certain... absolutely certain.... then the next most likely thing is the tach generator itself. Best to borrow one, and give it a try!
Failing that, you can use a AC volt-meter and pull the plug off the indicator and with the engine running check between one phase and another to try to see if one is missing. Like pin A to B, then A to C, and then B to C kind of thing. Voltages between phases should all be identical. Or close to it.
Lastly, it is actually possible to remove the tach gen, then CAREFULLY put the end into an electric drill and spin it to create the voltages that need to be checked. This is a really Rube Goldberg creation mind you, but I've done it once or twice.
Of course doing all of this with no spare parts to plop in and check makes the task much much more difficult. The best thing in the world is to just borrow a few parts to figure this out, but you can fervently hope it is just a bad solder joint, which it very well might be.
Bottom line, I've never seen an indicator fail. I've heard of one failing, but I've never seen it. On the other hand, I have seen many cases of failed tach generators, and failed wiring.
Mark
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Viperdoc
Joined: 19 Apr 2014
Posts: 484
Location: 08A
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| Posted: Sun Nov 05, 2017 11:52 am Post subject: [Non-DoD Source] Yak55M Tachometer |
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As Mark said. It is mostly a failure at on of the solder joints on the pin connection at the Tach Gen.
Doc
Sent from my iPad
[quote] On Nov 1, 2017, at 6:40 PM, Bitterlich, Mark G CIV NAVAIR, WD <mark.bitterlich(at)navy.mil> wrote:
The tach in the Russian airplanes uses a 3 phase AC system. The actions of your tach indicator point to one of the phases being intermittent or missing entirely. The typical place this fails is in the solder joint of the tach generator cannon plug itself. Not always mind you, but it is a good place to start looking. Lots of ways to check this. You can start by checking the wires with an ohm-meter by removing both the tach gen and tach indicator plugs and checking continuity.
If the wiring checks good... and you are certain... absolutely certain.... then the next most likely thing is the tach generator itself. Best to borrow one, and give it a try!
Failing that, you can use a AC volt-meter and pull the plug off the indicator and with the engine running check between one phase and another to try to see if one is missing. Like pin A to B, then A to C, and then B to C kind of thing. Voltages between phases should all be identical. Or close to it.
Lastly, it is actually possible to remove the tach gen, then CAREFULLY put the end into an electric drill and spin it to create the voltages that need to be checked. This is a really Rube Goldberg creation mind you, but I've done it once or twice.
Of course doing all of this with no spare parts to plop in and check makes the task much much more difficult. The best thing in the world is to just borrow a few parts to figure this out, but you can fervently hope it is just a bad solder joint, which it very well might be.
Bottom line, I've never seen an indicator fail. I've heard of one failing, but I've never seen it. On the other hand, I have seen many cases of failed tach generators, and failed wiring.
Mark
--
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
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