What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Suddenly all red X's on g3x system.

T

tomhanaway

Well Known Member
Two G3x touch screens, dual ahars, 307 auto, AOA, 23es transponder, etc. approx 25 hours in phase 1. Up until today, only minor squawks, all corrected. About 10 minutes into today's flight I started getting occasional red x's. Then, everything went red X including transponder and remote radio. Flew home using gtn 650 and ground speed from 650. Radio on gtn 650, which is not part of the canbus chain, worked fine.
On ground, booting up in config mode showed not a single unit had any check mark next to it. Neither red x or green check mark, just blank

The only thing I had done before this flight was pull the two main screens to check a serial #. Pulled both main screens and checked pins. All good. So reinstalled and all units were checking out green in config mode. Took plane up for a shakedown and everything worked fine.

So, my question is likely cause?

Would a break in the canbus chain, perhaps aggravated by engine vibration, cause all units to go red x?

Flying again tomorrow but want to start thinking about trouble shooting if it should happen again.

Thanks,
Tom H.
 
I've been curious about failure modes in the garmin can bus for a while. I realize that technically it's the right solution but I don't understand the implementation well enough to know how and why it fails. I believe one thing Dynon has done is to have redundant can bus networks, I wonder what mitigating efforts Garmin has used.

Looking forward to hearing from the Team X guys on this one.
 
Sounds like you had a shorted out CAN bus or lost part of your bus along with the terminating resistor for one end taking the whole bus down.

There are options for backup links in key places depending on what equipment you have.
 
Last edited:
I had similar problems when I first installed my G3X system. Seemed to occur when I pulled a few g's. As I found out, if one of the shield strands contacts one of the bus wires, it shorts out the whole system. Of course with it being intermittent it is difficult to isolate.

In my case when I first wired the bus I was stripping the outer sheath by cutting around it with a knife instead of cutting down the length as shown in Stein's video. When cutting around (as opposed to down the length) there is a much higher risk of making a small cut into the insulation of one of the wires, and because that is at the exact same location of where the shield gets rolled back against the outer sheath, contact between the shield and the exposed wire occurs.

I redid all the Can Bus connections, and in the process I found one small cut in a Can Bus wire at the location where the shield is folded back over the sheath. It has been solid ever since.
 
There are 232 ports available on the displays and ADAHRS units to provide backup communications between the ADAHRS and displays in the event the CAN bus fails, but you have to wire them for them to work (they are listed as "optional"). You will still lose the other "stuff" but the important flight data items will keep working.
 
tomhanaway said:
Two G3x touch screens, dual ahars, 307 auto, AOA, 23es transponder, etc. approx 25 hours in phase 1. Up until today, only minor squawks, all corrected. About 10 minutes into today's flight I started getting occasional red x's. Then, everything went red X including transponder and remote radio. Flew home using gtn 650 and ground speed from 650. Radio on gtn 650, which is not part of the canbus chain, worked fine.
On ground, booting up in config mode showed not a single unit had any check mark next to it. Neither red x or green check mark, just blank

The only thing I had done before this flight was pull the two main screens to check a serial #. Pulled both main screens and checked pins. All good. So reinstalled and all units were checking out green in config mode. Took plane up for a shakedown and everything worked fine.

So, my question is likely cause?

Would a break in the canbus chain, perhaps aggravated by engine vibration, cause all units to go red x?

Flying again tomorrow but want to start thinking about trouble shooting if it should happen again.

Thanks,
Tom H.
Click to expand...

Hello Tom,

Yes, what you describe is likely an issue with your CAN bus but as others have said, this doesn't normally result in loss of attitude, airspeed, and altitude because your system should be wired with an RS-232 backup data path from the GSU25 #1 to your PFD. Since you have dual ADAHRS and dual displays, you can even wire GSU25 #2 to the MFD in this manner and have yet even more backup capability.

Since a WAAS GPS is built into each of your displays, you don't even lose the navigation function if a CAN bus issue develops. Wiring should be the most reliable part of your system, but in the rare event a CAN bus problem occurs, you have lots of backup capability.

Your G3X Touch displays each have 6 serial ports, and serial port #6 is dedicated to providing this backup ADAHRS data path. Add the 3 wires shown on page 23-19 of the Rev. W G3X Installation Manual. The serial ports in both the GSU25 and the GDU 46X are already configured for this backup data bus.

Please email us and we will send you our CAN Bus Troubleshooting Guide and help in any way you need. It is probably something simple. The CAN bus is only 2 wires that daisy-chain to the CAN devices in your system.

Thanks,
Steve
 
Last edited:
Brantel said:
Walt and Steve beat me to it.

I can tell you I have tested the backup links and they work well.
Click to expand...

Same here. Like G3Xpert recommended, I have my ADHRS1 connected via serial to my PFD, and ADHRS2 connected to the MFD. I've also confirmed that it works when the CANBUS is down (tested by disconnecting the AP servo, which has the CANBUS terminator)

Also, I have GPS antennas connected to both the PFD and MFD, so even with a total CANBUS failure, I'll have all primary flight instruments and GPS.
 
I also have the RS232 backup link to the ADHRS and it worked well enough when I lost the CAN bus. However I also lose all my engine info as well as the AP. If this were to happen in the soup it sure would be nice to have a way for the AP work. I would be more tempted to change out my GRT Mini for the G5 if it allowed the AP to continue to work with a CAN bus failure.
 
You must log in or register to reply here.
Back
Top