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G3X EFIS Fuse Popping

Frac0220

Frac0220

I'm New Here
Hello all!

Wanted to reach out to the wealth of knowledge here and see if anyone could help with a problem we are having.

My fellow co-owner got stranded in 6J4 with our RV-12iS today. After getting fuel, hopped in, started the engine up, and right after the engine turned over, both G3Xs went black and tripped the 7.5 Amp EFIS fuse.

We tried to diagnose this as best we could, replacing the fuse, starting the engine with the EMS Backup, etc. Each time, it would trip the fuse. Tried removing and reinstalling the 30 AMP Main Fuse and the same thing happened.

My suspicions have me wondering if we have an issue with the Garmin G3X Backup battery or one of the Gens.

Any guidance would be greatly appreciated!
 
The EFIS circuit is pretty simple.. It supplies power to the PFD, MFD, the GEA24 (firewall-mounted box to monitor engine / discrete inputs), EFIS battery, magnetometer and the ADAHRS unit under the baggage area.

It is likely a wire that has chaffed and is grounding out. So, I'd advise removing the fuse.. putting a ohmmeter on one of the fuse terminals.. (whichever is grounded out).. and start to unplug things.. and watch to see when the power wire is no longer grounded out.. but more than likely, it is a wire that has chaffed and is now touching something metal.. not a device that has an internal short.. so slowly and deliberately jiggle the wires going to these devices and try to localize the problem to a certain area. You'll likely be able to put some electrical tape around the wire to make it good enough for a normal flight home.

Although I don't recommend it, if its a short enough trip, the plane could likely be ferried back home safely with the fuse removed. However, in order for the EFIS to actually use its EFIS battery.. you'll need to turn the MASTER OFF and the EFIS BATTERY to ON -- so you won't have radios, xpdr, lights, etc (which would be legal if daytime and ADSB is not required where you are). Unfortunately this is a wiring design error that I reported to Van's last year. If you choose to do this, dimming the G3X will save a little power too.

The EFIS battery will power the PFD (1.25A [backlight set to 100%]), EMS (0.43A), GPS 20A (0.2A), magnetometer (0.1A) and AHARS (0.2A) = 2.2A and the EFIS Battery is 3AH.. so clearly you'll have a full hour of power.. and likely 80 minutes or so, if fully charged.
 
Replace the blown fuse with a test light, the kind of light that does not have an
internal battery, only a light bulb. Harbor Freight has one for $3.99
https://www.harborfreight.com/612v-circuit-tester-with-5-ft-lead-63603.html
How do you replace a fuse with a test light? By making an adapter. Break apart a
blown fuse to get the terminals. Solder a wire to each terminal. Now connect
the test light to the two wires that are now hanging from the fuse panel.
Then watch the test light as you wiggle wires. When the light goes out, you
have found the short circuit. One suspect area is the over rudder wireway.
That wireway is held in place with a screw that has sharp threads that cut into
wire insulation. Replace that screw with one that has a smooth shank:
AN525-8R12. One RV-12 owner had a short circuit and replaced that screw
with a nylon one. It is not a structural part that requires strength.
Van's needs to issue a service bulletin for everyone to replace that screw.
 

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We had this happen and it was the EFIS fuse wire inside the cabin tunnel that attaches to the EFIS fuse. It was chaffing on the metal coil sheath cable for the co-pilot cabin heat control. The wires in the tunnel are tie-wrapped to the metal sheath coil and the EFIS wire from the fuse to the split to both G3X's is the one wire that was chaffing. I fixed the wire then put some rubber hose around the metal coil to prevent any other wires from chaffing.
 

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Thank you for all the knowledge here! We just borrowed a fellow RV-12 owners trailer and got the airplane back to our base late last night.

We haven’t had a chance to troubleshoot this with our mechanic yet, but I wanted to be more specific on what exactly was happening.

We replaced the fuse last night and the G3Xs come up just fine with the Master on and they stay on. Once you go to start the engine and turn the key, they will stay on until you let off the key. Then they go blank. So we are not sure if this is related to a stater relay, engine vibration jiggling a chaffed wire once the engine is started, or possibly something else.

We are going to work on it this week and report back.
 
Bring a trailer.com

I was glad you got your plane home in one piece with only a little drama. Those kinds of trips will remembered for a lifetime 😉. This is the second time my trailer has transported a plane other than mine. Turns out a 7A can fit the trailer too, but we didn't put the wings on the racks, they rode in a pickup truck. Here's hoping for a speedy return to flying.
 
<SNIP>

Our mechanics didn't get a chance to look at our airplane this week but plan to start looking at it next week.

I ran into them today and was able to explain what was going on. I also went out to the airplane to test and see what I could find out to be specific with our guys to send them down the right path to a solution.

I replaced the 7.5 amp EFIS fuse with a spare that was ordered from Van's. I could hit the Master and the screens would come up fine. I also tested the backup battery and the main PFD came up fine. I decided to shake the airplane around a bit to see if the short could make a connection and nothing happened. So I decided to try and run the starter with both Lanes Off. As soon as I turned the key, the EFIS fuse popped and the screens go dark. I replaced the fuse again, and reset for the same scenario and now each time I turn the Master on, the screens stay dark and will pop a fresh fuse.

I sent an email to Aric at Van's and have not heard back from him yet either.

Any ideas or suggestions with this new test? I got the wiring diagrams out and tried to figure out how the starter engaging would pop the EFIS fuse. I'm at a bit of a loss.

Thank you all for the help!
 
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If the fuse is now faulting regularly, as suggested before, check the LOAD SIDE of the fuse to ground and see if you don’t have a sustained ground.
 
Frac0220 said:
<SNIP>
As soon as I turned the key, the EFIS fuse popped and the screens go dark. I replaced the fuse again, and reset for the same scenario and now each time I turn the Master on, the screens stay dark and will pop a fresh fuse.
Click to expand...

I don't see how either. I think the act of engaging the starter is ever so slightly moving a wire bundle.. fraction of a millimeter ad grounding our a wire that already had its insulation worn off.

You'll likely need to remove the PFD/MFD, and probably even the instrument cover panel to get a good look at everything behind the glass.

I had a similar problem last year -- engaging the starter started to blow the 30A Generator fuse. It turned out that a wire coming through the firewall was touching the thumbscrew of a d-sub connector on the GEA24 engine monitor box. The knurled thumbscrew chewed away at 1 wire for about 400 hours before problems started occuring. After cleaning the soot off of the wire, it looked like a tiny pinhole-sized hole in the insulation.. that made contact only when the prop started to turn (like.. 1-2 rotations)...
 
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Frac0220, Remove the screw that holds the over-rudder wireway in place and see if the fuse still blows.
 
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