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Transponder Failure— GTX 23 ES

Auburntsts

Well Known Member
My remote mounted Garmin GTX 23 transponder failed right after takeoff tonight. I was on an IFR return flight from South Carolina to Tampa after taking my son back to college. Got a red X on my G3X PFD about the same time I made my initial call to approach. I cycled power on the G3X and the 23 and it sort of came back. It was broadcasting my squawk but no mode C. I still had a red X on the PFD and when I hit the xpdr soft key all of the functions we grayed out and unavailable so I had zero control over it (codes, modes and identity). After I got back to Tampa I tried cycling the power again but no luck. I went into the G3X setup and it showed that it wasn’t receiving any transponder data. Anyone ever have this happen? I suspect the unit is simply Tango Uniform, but the failure mode seems odd to me. I’ll have to pull it and get it to a shop to verify.
 
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No to you your question, but I would consider it an opportunity to (possibly) upgrade to something that will communicate with my 650. That's just me.
 
No to you your question, but I would consider it an opportunity to (possibly) upgrade to something that will communicate with my 650. That's just me.

Not following you. What communication are you referring to? Are you talking about using the 650 as a control head? If so what would be the benefit over my current config where my PFD is the control head?
 
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My remote mounted Garmin GTX 23 transponder failed right after takeoff tonight. I was on an IFR return flight from South Carolina to Tampa after taking my son back to college. Got a red X on my G3X PFD about the same time I made my initial call to approach. I cycled power on the G3X and the 23 and it sort of came back. It was broadcasting my squawk but no mode C. I still had a red X on the PFD and when I hit the xpdr soft key all of the functions we grayed out and unavailable so I had zero control over it (codes, modes and identity). After I got back to Tampa I tried cycling the power again but no luck. I went into the G3X setup and it showed that it wasn’t receiving any transponder data. Anyone ever have this happen? I suspect the unit is simply Tango Uniform, but the failure mode seems odd to me. I’ll have to pull it and get it to a shop to verify.

I would first check the wiring to the G3x. I suspect that the 23 might go to mode A (squawk with no altitude) if it loses the air data (i.e. altitude info) from the GSU25. This could explain why the transponder is still working but unable to be commanded by the G3x. It could also be the circuitry in the 23 that is responsible for controlling the RS-232 port.

Larry
 
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I would first check the wiring to the G3x. I suspect that the 23 might go to mode A if it loses the air data (i.e. altitude info) from the GSU25.

I plan to as anything is possible (pins and wires can break from vibration over time) and obviously this would be the least expensive fix. However I’m not holding out hope that that’s the problem especially since I haven’t had any issues in 5-1/2 years of flying with it.
 
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If you end up with a failed 23 you may consider installing the 45R, benefits would be remove the GDL and antenna, traffic weather available on all screens (touch only) plus to the 650. Would take a little extra wiring to make it all talk but not that bad.
 
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Not following you. What communication are you referring to? Are you talking about using the 650 as a control head? If so what would be the benefit over my current config where my PFD is the control head?
Like Walt said below. My 650 won't accept weather or traffic, or other communications to/from (my Garmin) experimental hardware.
If you end up with a failed 23 you may consider installing the 45R, benefits would be remove the GDL and antenna, traffic weather available on all screens (touch only) plus to the 650. Would take a little extra wiring to make it all talk but not that bad.

I plan to as anything is possible (pins and wires can break from vibration over time) and obviously this would be the least expensive fix. However I’m not holding out hope that that’s the problem especially since I haven’t had any issues in 5-1/2 years of flying with it.

Ya never know. Stein wired my panel and major components. Even so, for some reason I tested each terminal in every connector by pushing on the end. I found 4 that could be pushed out. I always wondered if they would have ever caused an issue.

Probably easier to swap a box, or bench test to see if it is really the transponder.

I hope you get straight to it, and fixed!!
 
Transponder Mode Failure

Like Walt said below. My 650 won't accept weather or traffic, or other communications to/from (my Garmin) experimental hardware.




Ya never know. Stein wired my panel and major components. Even so, for some reason I tested each terminal in every connector by pushing on the end. I found 4 that could be pushed out. I always wondered if they would have ever caused an issue.

Probably easier to swap a box, or bench test to see if it is really the transponder.

I hope you get straight to it, and fixed!!

It is worth taking a look at the connection between the GSU 25 and the transponder. As correctly suggested above, if the transponder loses its connection to the GSU 25, which provides pressure altitude to the transponder, it would retain its most recent squawk code and would continue to reply to Mode A interrogations.

Let us know if nothing turns up there and we can continue to look into it with you.

Thanks,

Justin
 
It is worth taking a look at the connection between the GSU 25 and the transponder. As correctly suggested above, if the transponder loses its connection to the GSU 25, which provides pressure altitude to the transponder, it would retain its most recent squawk code and would continue to reply to Mode A interrogations.

Let us know if nothing turns up there and we can continue to look into it with you.

Thanks,

Justin

Justin,
I get losing the GSU (a 73 in my case, not a 25) causing the loss of Mode C but would that also drive the red X on the PFD and complete loss of control of the transponder?
 
I had this happen with one of Garmin's faulty software updates. I landed, recycled everything and it came back online. When I got back home, I installed an earlier version of the software until Garmin released a new update that addressed the issue. I would add a software version check to the things to look into.
 
Epilogue

Well I fixed the problem. The connector on the back of the tray was loose to the point when I touched it, it fell off. First thing I did was reattach the connector, fired everything up, and everything functioned normally—whew! After shutting everything back down it was time to investigate why the connector had come loose. The connector attaches to the back of the tray from inside the tray via two small screws vs. external knurled knob D-Sub screws most of us are familiar with. After pulling the transponder out , I found both connector screws lying in the bottom of the tray. Turns out I apparently used screws that were too short by mistake. I guess that I got just enough thread engagement to hold the connector on temporarily but at some point they both backed out and eventually the connector itself became loose enough to cause my inflight failure.
 
GTX Control from GDU

Justin,
I get losing the GSU (a 73 in my case, not a 25) causing the loss of Mode C but would that also drive the red X on the PFD and complete loss of control of the transponder?

Yes, remote control of the transponder is facilitated through the same RS232 connection to the PFD that provides the GTX with pressure altitude. If that connection is broken, you lose control over the transponder from the G3X Touch, and the XPDR field would be Red X'd.

Thanks,

Justin
 
We are experiencing something similar to your original scenario. Takeoff with working transponder. Touch and go at a different airport, and at about 500' on climb out, red X comes on the G3X transponder display. Land to diagnose. Everything in transponder settings on the g3x is grayed out. Did a couple flights afterwards which were all tracked on flightaware, which tells me the mode A was still working even though you couldn't manipulate the code. Ordered a refurbished transponder, still same red X. Tested power and ground wires to the transponder, all good. Reverted to older software on the g3x and did a flight after, and suddenly nothing is being tracked on flightaware now. So I think the software change did something but it still doesn't explain the original problem when it was working fine on the beginning of the originating flight.

Ran a new wire from the gsu25 to the transponder with no change. Checked the antenna connection and it was secure. The current theory is the gsu25 is somehow bad but everything else besides the transponder is still working normally on the g3x. Also ran new wiring and pins from the connector to the transponder so I believe we can rule out wiring. So what else is there to test? TIA.
 
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