What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RV12iS kit GARMIN avionics intercom problem

As our first RV-12IS is nearing completion and we complete our final tests, we are having trouble with the co-pilot intercom only.

The problem I am struggling to solve is with the intercom. Pilot talks, copilot can hear. Copilot talks nobody can hear, no side tone either. Yet if co-pilot transmits on the radio the sidetone is apparent either way and the transmission is clear and strong.

The GTR200 is configured correctly. I have also back-to-back tested this radio in a known good airframe (a Tecnam) that I installed a GTR200 in a couple of years ago. It worked fine. So, the GTR200 is not faulty.

I am struggling to think of a wiring issue that could give you perfect radio transmit and receive along with correct sidetone, yet not deliver intercom to the pilot from the copilot.

I would greatly appreciate some help here. I am going to do some more troubleshooting tomorrow (Monday your time), as my focus is now back to what the harness pinouts are, and I would appreciate anything you have to suggest.
(This is a factory supplied Garmin Avionics package)
 
What Scotty McD said.

You've proven that the co-pilots mic and earphones are wired correctly to the GTR200.. so its a software setting at this point.
 
Scott and Rob, thanks for your reply.

Ashley has reposted my email above, and after 50-100 "set ups" of Dynon, Garmin Avidyne Trig etc systems, I have found any simple bugs are usually the low hanging fruit. And as you both point out the ICS pilot isolate is the lowest apple on the tree.

But can I restate these words.....The GTR200 is configured correctly. I have also back-to-back tested this radio in a known good airframe (a Tecnam) that I installed a GTR200 in a couple of years ago. It worked fine. So, the GTR200 is not faulty.

This means the GTR is actually correctly configured, these radios are dead simple, and I have double checked every parameter, along with a fellow avionics tech and the GARMIN SE Asia tech guru I know down here. That is why I back to back tested in a known good airframe. And with 6-8 different headsets.

The problem is the pre-made harness and or soldering, or perhaps the headset jacks have been squashed out of shape by the kids during assembly and something funky is going on. It is just strange the TX/RX are perfect.

When I find the bug, and I will, Ashley or I will repost for future reference, but in the interim anyone with an experience like this who has any tips on where to target next we would appreciate it.

Thanks in advance.
 
Here’s an odd suggestion: years ago I tracked down an audio panel problem to one of the ‘unused’ pins being grounded by the rack connector. It turned out the ‘unused’ pin was used at the factory to test (defeat) the squelch. So have you check that all ‘unused’ pins are actually not connected to anything?
 
As our first RV-12IS is nearing completion and we complete our final tests, we are having trouble with the co-pilot intercom only.

The problem I am struggling to solve is with the intercom. Pilot talks, copilot can hear. Copilot talks nobody can hear, no side tone either. Yet if co-pilot transmits on the radio the sidetone is apparent either way and the transmission is clear and strong.
Ashley,

I would start by verifying that the copilot mic jack is isolated from the panel and that the copilot MIC HI signal (pin 16 on GTR200, ring terminal at MIC jack) and MIC LO signal (pin 34 on GTR 200, sleeve at MIC jack) each have good continuity from end-to-end and are not shorted to ground or other connections.

GTR200 copilot wiring.png

Steve
 
Steve,

That is exactly what we will be doing today. I reckon that is the kind of bug we will find.
 
I should know better than to trust anyone. This is not the first time, in fact it is several down the list of pre fab harnesses being wrong from a so called reputable supplier. So my big mistake was trusting that.

All three connections on the co pilot mic jack were incorrect. not two but all three.

Works perfectly now.

Keep this in mind that harness builders make mistakes and you would think they make lots of harnesses, they should have very few mistakes. But in my experience this is not the case. Either that or I am a magnet for peoples problems. :)

Thanks guys.
 
I should know better than to trust anyone. This is not the first time, in fact it is several down the list of pre fab harnesses being wrong from a so called reputable supplier. So my big mistake was trusting that.

All three connections on the co pilot mic jack were incorrect. not two but all three.

Works perfectly now.

Keep this in mind that harness builders make mistakes and you would think they make lots of harnesses, they should have very few mistakes. But in my experience this is not the case. Either that or I am a magnet for peoples problems. :)

Thanks guys.

Glad you found it.
That was a strange one with it feeding mic audio to the radio to be able to transmit, but not in intercom mode.
 
Glad you found it.
That was a strange one with it feeding mic audio to the radio to be able to transmit, but not in intercom mode.

I too am curious to know what combination of wiring could result in the transmit audio (and PTT) working properly on transmit, but not on intercom mode. Can you say what was wrongly connected to what? Curious minds want to know.
 
Yeah, no kidding.

This is how it was wired Vs how it should be

Function Supplied Corrected to
MIC + WHT/ORG WHT

MIC Lo WHT WHT/BLU

PTT WHT/BLU WHT/ORG
 
Yeah, no kidding.

This is how it was wired Vs how it should be

Function Supplied Corrected to
MIC + WHT/ORG WHT

MIC Lo WHT WHT/BLU

PTT WHT/BLU WHT/ORG

Got it, thank you.
So the mike hi line was connected to the usual mike lo, and the PTT was connected to the usual mike hi jack. But the mike is not polarity sensitive. So when the PTT was pulled low, the transmit activated, the mike hi connection provided bias to the mike, with the ground return thru the PTT, and it all worked. But without the PTT activated, that line is at 10 volts or so, as is the bias from the mike high line, so there is no net bias on the mike element and it doesn’t work. You must have a PTT switch on the stick or panel; if you had tried a portable PTT plugged into the copilot jack, nothing would have worked, as the PTT line would never be pulled low. Interesting failure mode.
 
Exactly Bob.

I should have gone straight there in the first place. It was obvious the second I saw it. But the failure mode was interesting indeed.
 
Got it, thank you.
So the mike hi line was connected to the usual mike lo, and the PTT was connected to the usual mike hi jack. But the mike is not polarity sensitive. So when the PTT was pulled low, the transmit activated, the mike hi connection provided bias to the mike, with the ground return thru the PTT, and it all worked. But without the PTT activated, that line is at 10 volts or so, as is the bias from the mike high line, so there is no net bias on the mike element and it doesn’t work. You must have a PTT switch on the stick or panel; if you had tried a portable PTT plugged into the copilot jack, nothing would have worked, as the PTT line would never be pulled low. Interesting failure mode.

First: Bob, I'm very sorry you has this issue! I'm glad you were able to get it resolved quickly, but it shouldn't have happened.. If there's anything I can do to assist you please feel free to reach out to me directly.

We check the radios for Intercom functionality, alert audio, and com transmission. I would be willing to bet that the way this slipped through is the Intercom was check by one person listening for side tone, rather than talking to a 2nd person in the other headset. I'm going to talk to the team in the morning and ensure that we are always doing our audio checks as a team so this can't happen again. I know this won't retroactively fix your problem, but I want to do everything in my power to make sure we don't make this mistake again.
 
Back
Top