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  #1  
Old 03-17-2022, 09:57 AM
Bavafa Bavafa is offline
 
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Location: Sacramento, CA
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Default A complete CAN bus failure on Garmin

I was wondering if anyone has had any experience that one device brought down their entire system and prevented from loading?
I am not sure if my title, CAN bus failure, is correct but I had an anomaly with my GAD27 (flap issue) which Garmin decided to replace the device under warranty. The replacement GAD arrived a few days later and when I connected it to my system, the PFD would shut itself down immediately after booting up and nothing was working. My MFD would not shut down but everything had a big red X on it. Going back and forth between the old unit and the new, confirmed this is not a wiring issue as it would only do it with the new device.
They sent another replacement and that is working normal and as expected. But the fact that one device could cause the entire system to go down is not very reassuring to me.
Unfortunately, I did not pay attention to the G5 to see if I can keep that operational.
Hopefully Garmin will investigate this and see what is it with the unit that could cause such failure.
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  #2  
Old 03-17-2022, 12:41 PM
g3xpert's Avatar
g3xpert g3xpert is offline
 
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Default GAD 27 Problem

Quote:
Originally Posted by Bavafa View Post
I was wondering if anyone has had any experience that one device brought down their entire system and prevented from loading?
I am not sure if my title, CAN bus failure, is correct but I had an anomaly with my GAD27 (flap issue) which Garmin decided to replace the device under warranty. The replacement GAD arrived a few days later and when I connected it to my system, the PFD would shut itself down immediately after booting up and nothing was working. My MFD would not shut down but everything had a big red X on it. Going back and forth between the old unit and the new, confirmed this is not a wiring issue as it would only do it with the new device.
They sent another replacement and that is working normal and as expected. But the fact that one device could cause the entire system to go down is not very reassuring to me.
Unfortunately, I did not pay attention to the G5 to see if I can keep that operational.
Hopefully Garmin will investigate this and see what is it with the unit that could cause such failure.
Mehrdad,

The G5 internal ADAHRS is not reliant on the CAN bus to provide attitude and airdata information. This reminds me of a keep alive power issue we have seen in the past, can you please provide a brief overview of the power/ground path to your PFD?

Thanks,

Justin
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  #3  
Old 03-17-2022, 01:28 PM
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bhester bhester is offline
 
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Default CAN Bus can

A CAN Bus issue can take down the whole system. A bad solder sleeve can cause that, been there done that. I realize that is not what your issue was you had a bad component and Garmin should be able to recreate that when they hook it up in the shop.

I do not have a G5. I have an independent Dynon 10a and Aera 660. From what I've read the G5 should continue to work even with a CAN bus failure though.
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  #4  
Old 03-17-2022, 01:38 PM
Bavafa Bavafa is offline
 
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Default

Quote:
Originally Posted by g3xpert View Post
Mehrdad,

The G5 internal ADAHRS is not reliant on the CAN bus to provide attitude and airdata information. This reminds me of a keep alive power issue we have seen in the past, can you please provide a brief overview of the power/ground path to your PFD?

Thanks,

Justin
Hi Justin,
Thank you for chiming in here, it is good to know that the G5 would remain functional.
I have two source for power to the PDF, the primary goes to my avionics bus with the ground going to the central ground tabs.
The second power goes to the GAD 27, 273 lug 2. The keepalive power for GAD27 comes from the the PCW backup battery.
During the replacement and as part of the troubleshooting to see if anything else is causing this, I connected the replacement device to the connector P271 only and it still manifest itself in the same manner.

If you think my keepalive wiring is not correct or could cause issues and should be different, I would appreciate it if you can let me know.

Mehrdad
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  #5  
Old 03-17-2022, 01:59 PM
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Walt Walt is offline
 
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Default

Why would you have backup power (TCW battery) running thru the GAD27 rather than a direct connection to the PFD/GSU/GEA boxes?
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  #6  
Old 03-17-2022, 02:07 PM
Bavafa Bavafa is offline
 
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Default

Quote:
Originally Posted by Walt View Post
Why would you have backup power (TCW battery) running thru the GAD27 rather than a direct connection to the PFD/GSU/GEA boxes?
Walt,
Part of the reason was that the GAD27 has capacitor that can accomodate power surge and only PFD goes thru that. The rest of the component with dual power source go to my PCW as their second power. This also gives my GAD27 a second source of power as, if memory serves me right, GAD27 does not have dual power source.
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  #7  
Old 03-17-2022, 02:12 PM
PilotjohnS PilotjohnS is offline
 
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Default Valid

Quote:
Originally Posted by Bavafa View Post
Walt,
Part of the reason was that the GAD27 has capacitor that can accomodate power surge and only PFD goes thru that. The rest of the component with dual power source go to my PCW as their second power. This also gives my GAD27 a second source of power as, if memory serves me right, GAD27 does not have dual power source.
Unless you have test data, I dont think this is a valid reason to run thru the GAD27; to Walts point, it kind of defeats the purpose of a backup battery. JMHO

I would recommend following the Garmin schematic in the G3X manual. Many have done lots of analysis and testing of this design.
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Last edited by PilotjohnS : 03-17-2022 at 02:18 PM.
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  #8  
Old 03-17-2022, 02:30 PM
Bavafa Bavafa is offline
 
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Default

Quote:
Originally Posted by PilotjohnS View Post
Unless you have test data, I dont think this is a valid reason to run thru the GAD27; to Walts point, it kind of defeats the purpose of a backup battery. JMHO

I would recommend following the Garmin schematic in the G3X manual. Many have done lots of analysis and testing of this design.
I have no problem changing it but I like to hear what is wrong with the it first.

If I lose power and only rely on TCW, without GAD27 being powered up would I still have trim or flap control considering those go thru GAD27?
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  #9  
Old 03-17-2022, 03:29 PM
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g3xpert g3xpert is offline
 
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Default Wiring Diagram

Quote:
Originally Posted by Bavafa View Post
I have no problem changing it but I like to hear what is wrong with the it first.

If I lose power and only rely on TCW, without GAD27 being powered up would I still have trim or flap control considering those go thru GAD27?
Here is the reason I ask - We worked on one plane in the past, in which power was only being supplied to the PFD from the GAD27 keep alive output, which although against our general guidance, works as long as the GAD 27 itself is powered. When loading a software update that included new GAD 27 LRU software, the screen began a reset cycle as you described. The GAD 27 was attempting to update, which causes a brief reset of unit, which was interrupting the sole source of power to the PFD. As soon as the PFD came back up, it would try the update again, and repeat the cycle.

When replacing your GAD 27, is it possible you were only providing power through the backup battery <> GAD 27 path? If so, this could be the explanation for what you saw.

It may be a good exercise to send us a full schematic of this section of your system, and we can work through any questions you may have.

Thanks,

Justin
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Last edited by g3xpert : 03-17-2022 at 03:35 PM.
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  #10  
Old 03-17-2022, 03:35 PM
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g3xpert g3xpert is offline
 
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Default CAN Failures

Quote:
Originally Posted by bhester View Post
A CAN Bus issue can take down the whole system. A bad solder sleeve can cause that, been there done that. I realize that is not what your issue was you had a bad component and Garmin should be able to recreate that when they hook it up in the shop.

I do not have a G5. I have an independent Dynon 10a and Aera 660. From what I've read the G5 should continue to work even with a CAN bus failure though.
Agreed. Most of the time we see the whole bus go down, the bus itself is being shorted to ground. Component level issues typically only marginally affect the bus, resulting in autopilot disconnects or other more limited issues. Incorrect bus terminations can also cause significant communication errors.

When the bus is shorted to ground, a complete communication failure occurs. There are backup RS232 datapaths for both ADAHRS and EIS information that come in very handy should a CAN failure of any type occur.

Thanks,

Justin
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