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draftsjust417(at)gmail.co
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 Posted: Mon Sep 21, 2015 10:13 am Post subject: HS6/Chang Triplex Gauge |
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Hey Harv!
I recently spent several months finally refurbing a host of my CJ's electrical systems, neglected for decades.
Sounds like you've taken all the correct steps thus far, that is, swapping gauges front to back, checking cannon plugs, etc. Always start with the easiest and work to the harder!
Taking advantage of copiers at work, I enlarged the Chinese wiring diagrams (avail in the PLAAF manuals from Doug Sapp, chapter 7 "Aux Equip"). Initially very daunting, even for an aero engineer like me, but if you enlarge them to at least 11"x17", pour some strong coffee, make notes and trace wires with a hiliter, they actually make a lot of sense and the mystery gradually disappears. I came to better understand and respect the clever simplicity of the Chinese designs.
The Reds unwisely used 20-gauge white wire for nearly everything, which makes physical wire chasing difficult on the aircraft, but each wire should be ID'd with a 3-figure code on a clear sleeve at each end, ie - "3Y2", "7X12", etc. See photo of a typical sleeve on my bird, it states "14Y1".
The first 2 characters identify the system (landing gear lights, oil pressure gauge, etc) and the last digits are the actual individual wire. These wire codes are directly noted on the wiring diagrams and there's a very handy Table 7.1 in the manuals that explains each system's specific nomenclature (the 3Y, 7X, 25W, etc. See photo).
This will help you find the specific wire bundles and routing for these gauge gremlins.
Note that the wire diagrams are guides; they may have been produced years before your CJ was built, and won't necessarily reflect slight changes or repairs done decades ago by the military to your specific aircraft.
At this point, I'd suggest chasing each wire between the sender and its gauge... there may well be a chafed site that's short circuiting 1 wire, which will shut that system down.
Using a multimeter on the resistance/Ohm setting, you can measure the resistance of each wire in the bundle from one end to the other; that is, between sockets in the cannon plugs on each end. The cannon plugs' socket numbers are listed on the wiring diagrams (in a small triangle, if I recall correctly) with their corresponding wire's 3-character code. Insert a multi meter lead into the socket on one end, and the corresponding socket on the other end. There should be a small resistance reading, pretty much the same for each wire in the bundle. If anything shows an infinite resistance, then there's your defective and/or shorted wire.
( Most likely its rubbed up against structure over the years, has worn thru the wire's insulation, and is shorting at that site. I've found this several times in my CJ. Its a very simple fix to cut out the chafe site and install in a butt-splice. Very small chafes that have very minor wire damage might be able to be tape-wrap repaired. Of course, you'll want to find a way to protect the wire from further chafing here. )
So, in your case, this is how I'd go about it as a next troubleshooting step. Hope this helps-
Justin Drafts
N280NC
On Mon, Sep 21, 2015 at 4:29 AM, Harv <martin.harvey(at)kbr.com (martin.harvey(at)kbr.com)> wrote:
| Quote: | --> Yak-List message posted by: "Harv" <martin.harvey(at)kbr.com (martin.harvey(at)kbr.com)>
Thanks
I'm certain it's a wiring problem as the gauges behave normally when put into the rear cockpit, probably a bad joint at one of the cannon plugs on the front loom.
I'm not sure though how to debug? I've unscrewed the plug ends and eyeballed the internal joints which look ok. My idea is to now test the cannon sockets one by one, so socket connection pin marked as 1 goes to the other end of the wiring loom which is also marked as 1 on that cannon plug?
I will have to dig through my wiring diagrams.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=447290#447290
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Harv
Joined: 01 Jul 2010
Posts: 172
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| Posted: Tue Sep 22, 2015 2:07 am Post subject: Re: HS6/Chang Triplex Gauge |
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Again thanks for support.
I do have the complete set of maintenance manual from Doug but cant lay my hands on them right now.
Would someone be willing to scan the electrical system wiring diagram and post it on here? I have a copy of this too but its not readable due scan quality.
I do know the transducers are items designated 4Y & 10Y respectively and these seem to carry the following wire designations:
Pin 1 = wire is tagged as 4Y1
Pin 2 = wire tagged at 4Y2
Pin 3 = wire seems to be tagged 3YZ? (Earth, grounding wire?)
The other transducer carries similar wire designations led with 10 as opposed to 4.
Pin 1 = 10Y1
Pin 2 = 10Y2
Pin 3 = 9YZ? (Earth, grounding wire?)
What I would like to establish is where the earth (grounds) are terminated on the airframe. This entire problem could be a corroded earth which id like to rule out next.
Rgs
Harv
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