Mark Dickens

Mark Dickens

Well Known Member
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I have a problem and would like to see if anyone else has seen this. Basically, the GTN-650 comm has low level hissing overlaid with rapid clicking. It's in the background and goes away when receiving a transmission. This is with all power turned off in the workshop to eliminate any local interference from fluorescent lights, etc. I wonder about the cooling fan on the 650 as it is running.

Any ideas?
 
Mark,
I just finished the final checkout of my GTN-650 and I can tell you my unit is dead silent when not receiving even with my shop lights on.
I did have to turn up the squelch a bit from the default but I can still recieve transmissions while in my garage with antennas on the belly of the plane.

During my checkout, I did find I had a few pins wired wrong. Not hard to do with my poor eyes and those high density pins. Double check those fan pins. Maybe one is misplaced.

Other than the squelch, I can't offer anything else.
 
I unplugged the cooling fan and it didn't affect the hissing and clicking so it's not the fan...the search continues!
 
Hello Mark,
it sounds as if there is some noise being picked up somewhere, the first thing to do is isolate the GTN.

Do you have the aircraft on a power cart or checking with just the battery?
once you hear the noise I'd recommend pulling breakers on other units in the panel to see if anyone of these clears.

if it's a ticking noise my suspicions will be the transponder in the plane as these sometimes cause issues like this.

the next step is to look at the power and ground with an O'scope to see if there is noise on the line that may be causing this.

Let me know
 
Thanks Trek.

Here's what I've done:

Unit running on battery power alone

1. Turned off all power in workshop, including flourescent lights - No Change
2. Turned off all other devices (via VPX) and avionics on plane - No Change
3. Temporarily unplugged GTN 650 cooling fan - No Change
4. Turned off GTN 650 Main power via VPX - No Change
5. Turned off GTN 650 Nav unit via VPX - No Change
6. Turned off GTN 650 Comm unit via VPX - Sound Ceased
7. Unplugged GTN 650 antenna - No Change
8. Turned GTN 650 Comm volume down - No Change

When receiving a transmission, the sound goes away and fades back in when the transmission is completed. When speaking on the intercom, the sound goes away and fades back in when completed.
 
Interesting that the sound "fades" back in.

Does the radio have aux audio inputs, that would be normally blanked out when a transmission is received on the selected frequency??
 
Mike S said:
Interesting that the sound "fades" back in.

Does the radio have aux audio inputs, that would be normally blanked out when a transmission is received on the selected frequency??
Click to expand...

I don't recall if the GTN 650 has those inputs, but I'm not using them. Basically the 650 is connected to the Dynon SV-INTERCOM-2S. I assume that when a transmission comes in, it's the 650 doing the "fading" and when I speak on the intercom, it's intercom doing the "fading"
 
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Thanks Mark,
I spoke with one of our GTN software engineers this afternoon about this and he asked some of the following questions:
1. Does he notice if the squelch is closed and this clicking/hissing is a faint background noise?

2. If the squelch is closed and the clicking/hissing noise is faint then what happens if he opens the squelch, is the hissing and clicking noticeable with squelch open?

3. What model audio panel, if any, is he using?

4. Does he have any new LED lighting that is turned on?

5. If he has new LED lighting can he turn it/them off?

6. Does he have something like an I-pad or another tablet or even a cell phone running either on its own battery or on a DC adapter?

7. If yes to # 6 can he turn all devices in item 6 off.

8. Does he have transponder or ADS-B transmitter turned on? If so have him turn it/them off. There were some audio panels that picked up Xponder/ADS-B and this clicking sounds like this could be the noise source.

9. If he tightens the squelch does the hissing clicking noise decrease or stop altogether?

I know some of these have been answered however we're just not seeing any smoking guns here to come to any conclusion. but the clicking as I indicated has been reported from transponders and traffic boxes since they do transmit on a regular basis like this and if we don't have enough grounding between the units we may pick this up. the next step is to remove the unit and get with a Garmin dealer to see if they can install it in another airframe to see if the problem can be duplicated, and then check it on a bench. if it persists in these applications then it's very possible that a problem could be internal in the unit.

Let me know if there are any other questions,
 
Does the Dynon SV intercom have a "fail safe" provision? (e.g. puts radio straight thru with intercom power off).
If the answer is yes, turn the intercom off and try again. (you said you tried turning everything off - did that include the intercom?). The symptoms sure sound to me like some noise is coming thru on the SV's music channel.
 
Give the man a cigar!

BobTurner said:
Does the Dynon SV intercom have a "fail safe" provision? (e.g. puts radio straight thru with intercom power off).
If the answer is yes, turn the intercom off and try again. (you said you tried turning everything off - did that include the intercom?). The symptoms sure sound to me like some noise is coming thru on the SV's music channel.
Click to expand...

Yep, here's a smoking gun...turn off the SV intercom and all you get is a very faint high pitched whine in the background, no hissing or clicking. I turned off the squelch on the GTN to verify that the channel was working. Turn the intercom back on and it's back to hissing and clicking.

Now, since if I turn off the GTN 650 comm, the hissing and clicking goes away should I conclude that the music channel is picking up noise from the GTN? Sounds like the GTN is the transmitter of the noise and the intercom music channel is the receiver? Does this make sense?
 
Mark Dickens said:
Now, since if I turn off the GTN 650 comm, the hissing and clicking goes away should I conclude that the music channel is picking up noise from the GTN? Sounds like the GTN is the transmitter of the noise and the intercom music channel is the receiver? Does this make sense?
Click to expand...

Could be, although I wouldn't be too quick to "blame" the GTN.
Did you wire up the music inputs to the SV? With multiconductor shielded cable with the shield attached to ground only at the intercom end, and not connected to anything at the far end? Are any digital (RS232 or ARINC) lines running close to the music cables?

Edit: Is pin 18 on the intercom "floating" off ground as shown in the manual? e.g., the jack must not be in electrical contact with the airframe.
 
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BobTurner said:
Could be, although I wouldn't be too quick to "blame" the GTN.
Did you wire up the music inputs to the SV? With multiconductor shielded cable with the shield attached to ground only at the intercom end, and not connected to anything at the far end? Are any digital (RS232 or ARINC) lines running close to the music cables?
Click to expand...

No, the music inputs were not wired up. All shields were grounded at the intercom end at pin #1 per the instructions. The reason I point my finger at the GTN is that when I remove power from the comm section only (I have the main, comm and nav sections on separate VPX power pins), the noise ceases. Aside from turning off the audio panel, it's the only way to turn the noise off so logically, it's involved.

Tomorrow, I plan to start removing pins from the connector to try and isolate which pin the noise is coming in on. I have the nav audio coming in on pin 4 which is a muted input and since this noise does mute when a transmission occurs, it's a prime suspect. I'd almost bet that removing that pin will make the noise go away...
 
Couldn't stand it and went out and removed pin 4...yep, that's where the noise is coming from. Now, I need to pull the GTN harness and check that connection.
 
I suppose you tried to see if the GTN nav volume has any effect?

Personally I would put the nav audio on an unmuted input...
 
BobTurner said:
I suppose you tried to see if the GTN nav volume has any effect?

Personally I would put the nav audio on an unmuted input...
Click to expand...

Yes, no effect unfortunately, and I checked to make sure that pin 4 is wired right and it is. As for putting it on an unmuted input, the reason I wanted it muted was in case ATC calls in the middle of identifying a VOR/LOC. I wanted ATC to have priority. But I will switch it to the unused unmuted input just to see if there's a change.
 
You may have a huge impedance mismatch since you hooked up the GTN's NAV radio output to the muting input. I have no idea how the Dynon intercom is made but this could be a possibility.
 
Brantel said:
You may have a huge impedance mismatch since you hooked up the GTN's NAV radio output to the muting input. I have no idea how the Dynon intercom is made but this could be a possibility.
Click to expand...

Interestingly, the SV documentation doesn't mention impedance, but all of the other inputs work fine with both the GTN (500 ohm) and the SV comm. Unplug that input pin and everything is fine. The GTN comm is generating this noise and for some reason, the aux input is picking it up.
 
Mark Dickens said:
. As for putting it on an unmuted input, the reason I wanted it muted was in case ATC calls in the middle of identifying a VOR/LOC. I wanted ATC to have priority. But I will switch it to the unused unmuted input just to see if there's a change.
Click to expand...

I have found, at least around here, listening to ATIS or transcribed wx on a muting input to be an exercise in futility, as the ATC frequency is very busy, with the result that you have to listen to 20 cycles to get the whole message. But if you have ATC and the VOR on together, and you set both volumes to nearly the same, your brain is pretty good at listening to what you want to hear; if ATC calls, you'll hear it and switch your attention back to them. Same goes for music; unmuted, but I keep the volume low.

BTW, no real need to ID VORs by morse code on the 650 - it decodes them for you, next to the frequency display.
 
I would suggest moving the nav audio to the known-good com input on the intercom. If the noise goes away, the issue is the intercom; if it's still there the issue is the GTN (or strange wiring pickup).
 
I've decided to worry about this later and install three toggle switches (com1, com2 and nav1) so I can turn off each audio channel as desired. Once I get the plane out of the workshop environment and establish that the issue is not in that environment, I'll pick this up again.

I spent some time with Christer at Stein Air on this and he pointed out that the GTN650 comm might be picking up some noise and simply passing it along, rather than originating the noise. Since the warranty doesn't begin until engine start, I can afford to wait and see if changing the environment helps.

Thanks to all, especially Bob for their help on this!
 
Mark Dickens said:
I've decided to worry about this later and install three toggle switches (com1, com2 and nav1) so I can turn off each audio channel as desired.
Click to expand...

I presume you haven't forgotten a DPDT switch to send PTT and mike signals to the selected transmitter.

FYI, I have a system much like you are describing except my intercom is home built, not the Dynon, and I do use the volume controls instead of switches to "select" the coms, the nav (I don't have the noise issue you have encountered) and the music, as well as AOA and the autopilot warning tones, all on non-muted inputs. It's a simple system that meets my needs and I'm perfectly satisfied with it.
 
BobTurner said:
I presume you haven't forgotten a DPDT switch to send PTT and mike signals to the selected transmitter.

FYI, I have a system much like you are describing except my intercom is home built, not the Dynon, and I do use the volume controls instead of switches to "select" the coms, the nav (I don't have the noise issue you have encountered) and the music, as well as AOA and the autopilot warning tones, all on non-muted inputs. It's a simple system that meets my needs and I'm perfectly satisfied with it.
Click to expand...

There's a lot to be said for KISS. I do have the DPDT switch installed and except for this little issue, everything else works fine.
 
GTN 650 on/off

Thread drift
I'm sure a forehead slap is comming

I have the GTN 623/635/650 Cockpit Reference Guide and read it
I have the GTN 650 AFMS and read it (bordering)

1) I can't find the GTN 650 full operations manual on the Garmin website

2) what button do you push/ twist/ hold to turn the GTN650 OFF while the avionics bus is still powered?

Thank you
Bob
 
That is not the answer I was hoping for ....sigh......
Previously when I turned on my battery master switch my two G3X screens would come on with the avionics master off because I have two TCW B/U batteries with pass-through power. To stop that I de-pined pin 6 on the IBB. Now when the master comes on the screens stay off. I can turn the screens on with the B/U batt switches, however now when I turn the battery master on the screens go off because main bus voltage is above the IBBS cut-in voltage and the B/U batteries drop off taking the screens with them.

Here is what I was hoping for
-Turn on both B/U batteries and get the screens/AHARS going
-Turn on battery master when ready to start (this is where the screens now shut off)
-Start engine
-Turn on avionics SW when engine running

Right now I have to turn the avionics master on to keep the screens alive during start so I wanted to keep the GTN 650 off. It sound like Garmin built the GTN 650 without the ability to shut it off....... really..... REALLY?

Back to the drawing board....

Bob
 
Second thought

G3X gurus,
My option is to re-pin pin 6 in the TCW battery. The G3X screens would come on every time I turn my battery master on, ... For whatever reason.
Two questions

1) does it affect the service life of the screens to have increased on-off cycles?

2) does it hurt anything if power is removed before the G3X screens are fully booted up?

Thanks
Bob
 
Move posts

Doug,
Any chance posts 24-27 could be moved to a separate thread. It may be of interest to others and I made a mistake not starting a new subject. Your call
Bob
 
bobmarkert said:
G3X gurus,
My option is to re-pin pin 6 in the TCW battery. The G3X screens would come on every time I turn my battery master on, ... For whatever reason.
Two questions

1) does it affect the service life of the screens to have increased on-off cycles?

2) does it hurt anything if power is removed before the G3X screens are fully booted up?

Thanks
Bob
Click to expand...

Hello Bob,

We are unclear on how your dual power inputs and the dual TCW battery backup systems are being wired, so we will send you an email rather than try to have that discussion over the forum.

The TCW manual provides guidance on using the battery backup system for the Power 2 pins and the avionics bus for the Power 1 pins, but it doesn't sound like this describes your installation, so we want to make sure we understand your installation before trying to provide guidance.

Thanks,
Steve
 
All better

My bout with temporary insanity is over! Funny how I got all honey- badgered about an enexpected behavior of my electrical system. Here is the amazing part.... Two private emails from the Garmin support team,.. The best decision I made was to go Garmin.....thanks Steve.

My B/U batteries were wired per plans and my G3X was functioning normally..... I just did not like the normal. I have 2 complete G3X systems, ADAHARS, Magnatrometers, 2 B/U batteries etc. this is a traveling machine with aux tanks.....
I wanted the ability to shut down half my system in flight and preserve one of the 2 B/U batteries until needed and then fire up the other half as the first battery depleted. That would give me 2+ hours of IFR B/U power. That could not happen with the standard wiring method. I've found a way to do that and I'm all better now. If anybody wants more info send private message or call. I don't need to bore everyone else with the details
Bob
[email protected]
303 882-7410
 
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