solder joints under clamp bars of strain relief

Several weeks ago I turned my master switch on to check my tach time and had red X's all over my G3X. Really spooky since my last flight included some IFR.


Thanks to the G3Xpert (Great help by the way), he pointed me to a CanBus shorting out somewhere. Pretty easy to track down to the connector on the back of the MFD by wiggling the wires. Nothing jumped out at me as shorting out when I took the connector apart, except for the 4 into 1 solder connection that was underneath the clamp bar strain relief on the connector.


I couldn't get the fault to repeat itself without the clamp bar on the connector, the solder connection was heat shrunk as well as bundled with several other wires and silicone taped prior to clamping. Pretty easy to see the indention of the solder connection underneath the clamp bar, it was about the size of a popcorn kernel.




I was also confused by the 4 CanBus wires spliced together at the MFD, my wiring diagram looked like this:




I had the original G3X harness made for me and added the rest of the equipment later. Garmin also revised their wiring recommendations on the CanBus, used to be able to have nodes something like 3 feet in length. When I added onto the CanBus adding the other equipment reference the wiring diagram I left the node to the GAD29 floating and daisychained the rest of the equipment starting at the GSU25 where the old termination was. Well the actual wiring had 4 nodes from the MFD, 1 to the PFD, GSU25I, GEA24 and the GAD29.
I cut the 4 way CanBus splice out and wired the CanBus per current recommendations without any nodes and used longer pigtails on the solder joints to place them aft of the connector and bending point of the wiring. So Far so good. I hope this fixes it.

My wiring diagrams though not 100 percent correct were very essential to tackling this problem, also make sure your solder joints aren't being clamped by the strain relief.

The G3Xpert also cued me to the backup RS-232 link from the GSU25 to the PFD so I won't lose my Primary flight instruments in case my CanBus goes down again.

Like you said, one solder joint could have really messed up your day if you were IFR. Thanks for posting. That makes me think about not getting careless when doing the small stuff.

blueflyer said:

Like you said, one solder joint could have really messed up your day if you were IFR. Thanks for posting. That makes me think about not getting careless when doing the small stuff.

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And this is why, if you're going to fly IFR, you want to have (and be current using) back up flight instruments that really are independent from your main PFD.

Agreed, I'm glad my backup is a totally separate independent system with a battery backup even though the secondary AHARS link would have provided primary flight instruments if this failure occurred again. I still like my odds over the standard 6 pack.

Yes, equipment does nothing without proficiency.

crabandy said:

The G3Xpert also cued me to the backup RS-232 link from the GSU25 to the PFD so I won't lose my Primary flight instruments in case my CanBus goes down again.

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I've seen this same type failure before where two soldered/heat shrinked wires shorted to each other under the clamp (one of the solder joints had a sharp point that jabbed through the heat shrink).

With G3X and dual ADAHRS/dual screens, if you have enough serial ports, I would recommend running the back-up RS232 on both, that will give you a very high level of redundancy for a PFD display.

When I couldn't find a short between the solder joint and the clamp bar I tried to dissect it further. I carefully cut the heatshrink from the joints but even with the heatshrink removed I couldn't find a single strand of wire that might have protruded through the Heatshrink. I carefully cut the heatshrink, peeled it off and searched the solder joint and traced the solder joint with my fingernail for any stray wires but found none. I'm not saying it wasn't possible, but I did everything I could to find a definitive short and couldn't find it. The CanBus short was 100% coming from that connector and that is as close to definitive as I can be. Nothing else stood out, I specifically checked the shield grounds to the CanBus and could produce no faults. That's why I'm stuck on the solder kernal that was smushed underneath the clamp bar. Time will tell.

Once again the system can have the technology to override the failure, the system and operator have to be aware of it. I thought I spent enough time and money, I should've spent more time cuz everything else was there! I'm just happy it's a learning opportunity!!

The main purpose of this post is that others think about:

- a secondary path from their AHARS to their PFD

-don't have solder joints under clamp bars or connectors

-have a totally separate backup system if flying IFR


Happy Flying !
Andy

Thanks!

Andy,

Thanks for the thread, especially like the photos! Great information for me as I complete my install.

Jim

G3Xpert question

Sorry to revive an old post, but I'm curious about the answer.

With a dual G3X touch with G5 backup and CanBus connection - what would a CanBus short or other failure mode look like on the three displays?

Also have a neighbor replacing a Dynon D-10 with a G5 in his legacy G3X panel and he asked the question. Is the answer different here?

Does using a backup RS-232 connection eliminate or minimize the failure?

Thanks!