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A complete CAN bus failure on Garmin

Bavafa

Well Known Member
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.
 
GAD 27 Problem

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
 
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.
 
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
 
Why would you have backup power (TCW battery) running thru the GAD27 rather than a direct connection to the PFD/GSU/GEA boxes?
 
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.
 
Valid

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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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?
 
Wiring Diagram

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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CAN Failures

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
 
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?

First off I think you would be asking too much of the little TCW battery to run everything plus flaps and trim.
The GAD also has separate power inputs for flap and trim, so you would lose those anyway if you lost primary power.

If you actually lost power, then the idea is to supply power to the primary instruments to give you enough time to get on the ground, flaps and trim are not necessary for that.
 
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
Hi Justin,
Although that situation seems very logical, it does not fit my case. For one, I had turned my avionics bus on so the PFD did not have GAD27 as the only source. I even connected my battery to a power supply thinking maybe my voltage is too low and causing this. I also connected only P271 (big connector) to the new GAD and again it caused PFD to shut down. The shut down did not seem to be a power cycle as I did not see it to come back up, although it maybe that I did not wait long enough.

The replacement unit was applied in the same manner and has been working without any issues. With the replacement unit I also noticed the message on PFD that it was updating the SW on that and that did not cause the PFD to go down.

Again, here I am just providing info and not by any means defending my wiring. If there is anything not optimum with my wiring, I have no problem changing it but would like to understand the logic of it rather than just change it because.....
 
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.

Just for clarity, and G3X guys please correct me if I'm wrong, but I'm pretty confident the GAD27 has a "brown out" feature which is likely a DC-DC power supply, its able to step up a low voltage input to 12v with some limitations. It definitely is not big enough to house a storage capacitor with enough capacity to do what it offers.
 
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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.

You wouldn't by chance be using a VPX bus system, would you? We have an RV-8 here with VPX and found out that one of the VPX outputs presented with a short shut down the whole avionics bus. The culprit was a bad USB Power port with a bad cell phone charge cable. We figured that out by unplugging the cable. So this was analogous to what you describe. We were incredulous that one little short on one of the VPX circuits would take down the whole electrical system. VPX never gave us a good answer as to why so and I am a "revert" to conventional electrical bus architecture.
 
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