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  #11  
Old 03-17-2022, 03:43 PM
Walt's Avatar
Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
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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?
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.
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Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 2000+ hrs, New Titan IO-370, Bendix Mags, MTV-9 prop
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  #12  
Old 03-17-2022, 03:52 PM
Bavafa Bavafa is offline
 
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Location: Sacramento, CA
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Originally Posted by g3xpert View Post
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.....
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  #13  
Old 03-17-2022, 03:55 PM
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Walt Walt is offline
 
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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.
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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Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 2000+ hrs, New Titan IO-370, Bendix Mags, MTV-9 prop
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154

Last edited by Walt : 03-17-2022 at 03:58 PM.
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  #14  
Old 03-17-2022, 04:19 PM
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jliltd jliltd is offline
 
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Location: Rancho San Lorenzo
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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.
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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  #15  
Old 03-17-2022, 05:00 PM
Bavafa Bavafa is offline
 
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Originally Posted by jliltd View Post
You wouldn't by chance be using a VPX bus system, would you?
No VPX, traditional bus system.
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