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GTN 650/G3xT not talking correctly...SLSA...help

G

Giving Wings

Member
I am at my wits end with chasing a problem. Background...we have two newish (2021 and 2023) RV12is SLSA. Recently we lost COM and NAV display on G3XTs. We also lost GPS position on the G3XTs. Diagnostics show. Red x on RS-232 Position 1 and 5, Plus an ARINC input issue. First we ruled out the low hanging fruit by swapping boxes (GTN, GDU, GAD 29) problem did not go away. Out comes the wiring diagram. PITA to get to the P1001 connector on the back side of the GTN. We check continuity between pins for position 1 and 5. Continuity is good. Signal ground continuity is good. After getting Aric involved at Van's they have run out of suggestions and suggest talking to Garmin....IF I don't find a chafed wire back in the twisted mess of harnessed going to the GTN, Autopilot, GMA. It is very tight back there. QUESTION: IF I HAVE CONTINUITY BETWEEN THE PINS WOULDN'T THAT MEAN I DO NOT HAVE A CHAFED WIRE?

The wasn't an intermitant error came back from a flight as a hard failure.
GTN still has GPS signal, COM and NAV and works as should.

Short of pulling the radio racks to get a good look at the radio stack end of the wires/connectors...anything else to check?

Thank you for any suggestions.

Eric
 

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If I understand it correctly, you have 2 RV‘s that are both having issues. Did I read this correctly? If so, did you do a recent software update on both?
 
Giving Wings said:
We also lost GPS position on the G3XTs.
Click to expand...

Everything else sounds like some kind of wiring issue, but this point stands out to me. Your GTN 650 should not be the only source of position data for your G3X system, so you must have some other GPS antenna installed, and any problems with that should be unrelated to the wiring of your GTN. Is it possible you are just experiencing poor GPS reception due to being in a hangar, or does this persist when outside?
 
Giving Wings said:
I am at my wits end with chasing a problem. Background...we have two newish (2021 and 2023) RV12is SLSA. Recently we lost COM and NAV display on G3XTs. We also lost GPS position on the G3XTs. Diagnostics show. Red x on RS-232 Position 1 and 5, Plus an ARINC input issue. First we ruled out the low hanging fruit by swapping boxes (GTN, GDU, GAD 29) problem did not go away. Out comes the wiring diagram. PITA to get to the P1001 connector on the back side of the GTN. We check continuity between pins for position 1 and 5. Continuity is good. Signal ground continuity is good. After getting Aric involved at Van's they have run out of suggestions and suggest talking to Garmin....IF I don't find a chafed wire back in the twisted mess of harnessed going to the GTN, Autopilot, GMA. It is very tight back there. QUESTION: IF I HAVE CONTINUITY BETWEEN THE PINS WOULDN'T THAT MEAN I DO NOT HAVE A CHAFED WIRE?

The wasn't an intermitant error came back from a flight as a hard failure.
GTN still has GPS signal, COM and NAV and works as should.

Short of pulling the radio racks to get a good look at the radio stack end of the wires/connectors...anything else to check?

Thank you for any suggestions.

Eric
Click to expand...
If you suspect a shafed wire, also check if
there is a short between pin 1/5 and GND.

Good luck
 
Hi Eric, you've got some good suggestions here.... to answer your question, does continuity indicate you don't have chaffed wires... no. As Avanza says, a chaffed wire would show as 'continuity' from pin 1 to 5, pin 1 to ground, and/or pin 5 to ground. You need to check for cross continuity, not direct continuity. Also, your last photo is another interesting clue... the GTN650 isn't receiving data from the GSU 25 ADHRS unit. I believe this integrates via the GAD29, so good advice from piot2512 to check that. Best though is the idea to talk with Garmin, especially as this is an SLSA. All maintenance must be done in accordance with the maintenance manuals or directions provided directly by the manufacturers.
 
Webb said:
If I understand it correctly, you have 2 RV‘s that are both having issues. Did I read this correctly? If so, did you do a recent software update on both?
Click to expand...
No, we have one with the issue. I have done all the "swaptronics" using the other one to rule out issues with the boxes.
 
brianb08 said:
Hi Eric, you've got some good suggestions here.... to answer your question, does continuity indicate you don't have chaffed wires... no. As Avanza says, a chaffed wire would show as 'continuity' from pin 1 to 5, pin 1 to ground, and/or pin 5 to ground. You need to check for cross continuity, not direct continuity. Also, your last photo is another interesting clue... the GTN650 isn't receiving data from the GSU 25 ADHRS unit. I believe this integrates via the GAD29, so good advice from piot2512 to check that. Best though is the idea to talk with Garmin, especially as this is an SLSA. All maintenance must be done in accordance with the maintenance manuals or directions provided directly by the manufacturers.
Click to expand...
The ADHRS unit does not have any things to do with the GTN populating the com and nav frequencies from the 650 though. Correct?
 
brianb08 said:
Hi Eric, you've got some good suggestions here.... to answer your question, does continuity indicate you don't have chaffed wires... no. As Avanza says, a chaffed wire would show as 'continuity' from pin 1 to 5, pin 1 to ground, and/or pin 5 to ground. You need to check for cross continuity, not direct continuity. Also, your last photo is another interesting clue... the GTN650 isn't receiving data from the GSU 25 ADHRS unit. I believe this integrates via the GAD29, so good advice from piot2512 to check that. Best though is the idea to talk with Garmin, especially as this is an SLSA. All maintenance must be done in accordance with the maintenance manuals or directions provided directly by the manufacturers.
Click to expand...
I have been working with Aric at the Factory. They seem to be suggesting I need to focus on the wiring behind the GTN/GMA/ GFC racks. It was a PITA just to get to the P10001 connector. Meanwhile the airplane is not out flying and we are loosing revenue. All functions of GTN are working just simply not populating COM/NAV/GPS signal to PFD.
 
On the G3X system information page are any of the boxes red xs, other than the GTN ones?

If you put the GTN into configuration mode (hold the home button when it starts up) and go to the system status page, are there any of the boards that aren't powering up (shown as just dashed lines)?

The way this is presenting, assuming the canbus is still solid, I am wondering if you lost power to pins 19 / 20 or ground at pins 77 / 78 on GTN connector P1001.

You can check this pretty quickly from the front with a voltmeter. We make make a quick probe tool in the shop by crimping a pin on a wire and taping it to some safety wire then connecting the wire to the voltmeter probe.
 
Last edited:
Giving Wings said:
The ADHRS unit does not have any things to do with the GTN populating the com and nav frequencies from the 650 though. Correct?
Click to expand...
That is correct. But you showed a photo that the GTN650 isn’t receiving altitude info from the ADHRS. That has everything to do with the GSU 25 and GAD 29 connectivity. Seems the issues aren’t just between the G3X and GTN 650
 
Giving Wings said:
I am at my wits end with chasing a problem. Background...we have two newish (2021 and 2023) RV12is SLSA. Recently we lost COM and NAV display on G3XTs. We also lost GPS position on the G3XTs. Diagnostics show. Red x on RS-232 Position 1 and 5, Plus an ARINC input issue. First we ruled out the low hanging fruit by swapping boxes (GTN, GDU, GAD 29) problem did not go away. Out comes the wiring diagram. PITA to get to the P1001 connector on the back side of the GTN. We check continuity between pins for position 1 and 5. Continuity is good. Signal ground continuity is good. After getting Aric involved at Van's they have run out of suggestions and suggest talking to Garmin....IF I don't find a chafed wire back in the twisted mess of harnessed going to the GTN, Autopilot, GMA. It is very tight back there. QUESTION: IF I HAVE CONTINUITY BETWEEN THE PINS WOULDN'T THAT MEAN I DO NOT HAVE A CHAFED WIRE?

The wasn't an intermitant error came back from a flight as a hard failure.
GTN still has GPS signal, COM and NAV and works as should.

Short of pulling the radio racks to get a good look at the radio stack end of the wires/connectors...anything else to check?

Thank you for any suggestions.

Eric
Click to expand...
The GAD 29, GEA 24, GPS 20A, GSA 28, GSU 25 units have an LED on their outer cases that indicates the LRUs current status.
G3X Installation manual, Table 31-1 Status LED Indications. PDF pg 739.

Good luck
 
brianb08 said:
That is correct. But you showed a photo that the GTN650 isn’t receiving altitude info from the ADHRS. That has everything to do with the GSU 25 and GAD 29 connectivity. Seems the issues aren’t just between the G3X and GTN 650
Click to expand...
The GTN gets airdata via the GAD29 ARINC which gets it either from the GDU via serial or ARINC or via canbus. I can’t remember and doesn’t really matter either way because if there was a GSU25 connectivity problem there would be red Xs all over the PFD.
I don’t think the GSU25 has anything to do with it.

I’d remove the unit and double check that the P1001 connector hasnt come loose from the back of the GTN rack.
 
Richard Connell said:
ts airdata via the GAD29 ARINC which gets it either from the GDU via serial or ARINC or via canbus. I can’t remember and doesn’t really matter either way because if
Click to expand...
That is correct. The GTN gets its airdata through the EFIS/Airdata ARINC port, which is on P1001. All of the failed data connections are common to GTN P1001, so that is where we should focus our attention.
 
Richard Connell said:
The GTN gets airdata via the GAD29 ARINC which gets it either from the GDU via serial or ARINC or via canbus. I can’t remember and doesn’t really matter either way because if there was a GSU25 connectivity problem there would be red Xs all over the PFD.
I don’t think the GSU25 has anything to do with it.

I’d remove the unit and double check that the P1001 connector hasnt come loose from the back of the GTN rack.
Click to expand...
GSU connections are good and green light is flashing as it should.
 
Giving Wings said:
I am at my wits end with chasing a problem. Background...we have two newish (2021 and 2023) RV12is SLSA. Recently we lost COM and NAV display on G3XTs. We also lost GPS position on the G3XTs. Diagnostics show. Red x on RS-232 Position 1 and 5, Plus an ARINC input issue. First we ruled out the low hanging fruit by swapping boxes (GTN, GDU, GAD 29) problem did not go away. Out comes the wiring diagram. PITA to get to the P1001 connector on the back side of the GTN. We check continuity between pins for position 1 and 5. Continuity is good. Signal ground continuity is good. After getting Aric involved at Van's they have run out of suggestions and suggest talking to Garmin....IF I don't find a chafed wire back in the twisted mess of harnessed going to the GTN, Autopilot, GMA. It is very tight back there. QUESTION: IF I HAVE CONTINUITY BETWEEN THE PINS WOULDN'T THAT MEAN I DO NOT HAVE A CHAFED WIRE?

The wasn't an intermitant error came back from a flight as a hard failure.
GTN still has GPS signal, COM and NAV and works as should.

Short of pulling the radio racks to get a good look at the radio stack end of the wires/connectors...anything else to check?

Thank you for any suggestions.

Eric
Click to expand...
Hello Eric,

Just to be sure, you mention 2 RV12's. I presume you are seeing this problem on only one of them, or is there a problem with both aircraft?

Is this a problem that recently developed on a previously working system, or has this always been an issue since you took delivery of the aircraft/finished the installation?

Is the VNAV message present on the GTN at all times? It is possible to see that message if the GTN were powered without the GSU 25 being powered.

Without knowing more about your configuration and wiring, you appear to have a problem with both the serial connection from the GTN to the GDU, as well as 2/3 ARINC 429 connections from the GTN to the GAD 29. In the absence of more information, it hard to say exactly what could be the cause of this. If you send us a configuration file, your wiring diagram and some pictures of your system information menu (configuration mode), we can probably help you get to the bottom of this pretty quickly. We can be reached directly at [email protected].

Thanks,

Justin

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