796 Noise

[OLDCROWE]

I'm getting constant noise in one side of my intercom music circuit(s) that seems to be coming in via the 796. It is a constant low pitch static, not like an alternator whine and it does not change with RPM.

Installation particulars:

• Super Cub panel with all a surface mounted 796 using all Garmin hardware and wiring to the fuse holder, from the fuse holder pigtail to the breakers is a soldered and shrink-wrapped standard aviation wire with no other splices.
• Sigtronics Intercom.
• XM Antenna that I move from plane to plane but the default location is not the Cub so this may have been going on awhile, but I've been noticing for better than a couple of years, but it had gotten worse.
• I like to fly with tunes so there is a mini plug for music that is internally switched (2) for two sources, XM is constant, and it magically overrides XM when you manually plug into it and connect your phone.

As I said the music circuit make a constant static roar (XM Antenna plugged in or not) but plug in a phone jack (phone or not) and all is clear.

What I have done so far:

• We relaced the music plug with the same (SWITCHCRAFT INC PN 35RAPC4BH3) and the static got better, perhaps reduced by 30% but it is still seriously annoying, before it was a roar.
• After flying with the new music plug in place and still having static without a mini plug plugged in, I made further attempts to isolate the noise. I again turned things off and back on and started pulling breakers with the engine running as you don't hear it otherwise and that's when it got interesting. Turning off the Trig Mode S (with Trig ADSB out) transponder makes no difference but pulling the Transponder breaker and all went quiet but the 796 went into battery mode so it was obviously on the same breaker.
• Thinking the common breaker with the transponder was the issue we moved the 796 to a different breaker. Tried that and no change in the noise, it's there anytime there is no music jack plugged in (I Phone connected or not) and pulling the transponder breaker makes no difference so I don't think that's the culprit, but who knows.
• Also, after moving the supply to a different breaker, I pulled the in-line fuse to the 796 and the noise went away.
• Pull the 796 and no noise, put it back in and noise.
• Pull the Transponder breaker and still have the noise.
• Swap the 796 with a different unit and same issue, so it's not the unit.

Looking for brilliant ideas, support groups or an intervention...

Many thanks,

Kirby

 

[sj]

Sounds like the power supply for the 796 is the culprit to me, unless I read it wrong. Temporarily try a different one through the cig lighter, or usb.

sj

 

[wireweinie]

Power up a couple of different 796's with a couple of wire harnesses. See if the problem follows the 796 or the harness.

Web

 

[mvivion]

It's been a long time since I liked Sigtronics Audio Panels.....

MTV

 

[OLDCROWE]

Power up a couple of different 796's with a couple of wire harnesses. See if the problem follows the 796 or the harness.

Web

I tried multiple 796's, I'll dig around for another harness.

 

[OLDCROWE]

It's been a long time since I liked Sigtronics Audio Panels.....

MTV

I'm confident it's not an intercom issue.

FYI - Model SCI-S4. Stereo with individual Volume and Squelch plus crew isolation. Great installation support, they specified the dual source music jack.

Wasn't my choice but I have had N0 complaints whatsoever about the unit itself and it has stunning sound quality.

 

[DENNY]

Make sure you have insulation washers on all the jacks.
Denny

 

[OLDCROWE]

Make sure you have insulation washers on all the jacks.
Denny

They do, it's a quality installation.

 

[wireweinie]

They do, it's a quality installation.

On all jacks? Mic, audio, and music?

Web

 

[OLDCROWE]

On all jacks? Mic, audio, and music?

Web

Yes. Initially the music switch/jack didn't but was in an oversized hole. The new ones did not come with washers and the threads are very short. We tested for noise with the switch/jack removed free from the panel (its mounted in the top of the map pocket next to a two port USB plug) and it was still noisy. Since it did make a little static noise when put it in the mount hole. It was difficult to mount in the oversized hole, so we re-drilled for a better fit and insulated it with electrical tape on both sides of the metal before installing it and put shrink wrap on the threads where it went through the metal plus the switch body is not metallic.

Also, I've cleaned the contacts on the 796 and the mount.

Web, my thought at this point is that the XM audio output line to the switched plug is picking up the noise it's coming otherwise into the 796 somehow.

As SJ suggested I'm going to try a different harness powered from a different source in the plane.

 

[wireweinie]

Yes. Initially the music switch/jack didn't but was in an oversized hole. The new ones did not come with washers and the threads are very short. We tested for noise with the switch/jack removed free from the panel (its mounted in the top of the map pocket next to a two port USB plug) and it did make a little static noise wo when put it in the hole. It was difficult to mount in the oversized hole so we re-drilled for a better fit and insulated it with electrical tape on both sides of the metal before installing it and put shrink wrap on the threads where it went through the metal.

Also, I've cleaned the contacts on the 796 and the mount.

Web, my thought at this point is that the XM audio output line to the switched plug is picking up the noise it's coming otherwise into the 796 somehow.

As SJ suggested I'm going to try a different harness powered from a different source in the plane.

If you need iso washers let me know! It's easier to send them to you than doing all that other stuff, lol.

Try a harness that plugs into a cigarette lighter plug, instead of the hard wire harness. Also check how the 796 and intercom wires are routed. Separate them if they are bundled together.

Web

 

[OLDCROWE]

Folks it's been a process where we isolated, replaced, wiggled and separated things and while waiting for the cows to come home a new quirk appeared. After we moved the 796-power supply to a different (1 amp breaker) with the intercom (you know the one Wireweinie hates) after a couple weeks the breaker started popping after a while (my joy was nonexistent) but the odd part was that the 796 was only lasting about 10-15 seconds on the battery. Humm, so I pulled the 796 battery out and it was HOT so I ordered a new battery from Garmin (actually two, one for each 796 in the fleet so Ouch!). I finally got around to installing them but before I did, I pre-charged them overnight on the Garmin desktop thingy then popped the unit in and Presto-Chango there was no Noise on my next flight!

My thought is the battery pack had been shorting for some time and in the process making a bunch of racket or it could just have been a Rosan Rosanna-Danna moment where it just goes to show, it's always something.

Anyway, many thanks for everyone's ideas, especially Steve Pierce's and Web's, and you're all welcome for my contribution to raising Garmin's profitability this quarter.

Kirby

 

[Steve Pierce]

I personally thought he had lost his mind, glad to know that wasn't the case. Just kidding. You can't make this stuff up though.

 

[cubdrvr]

I tried multiple 796's, I'll dig around for another harness.

.............and they all had bad batteries?

 

[OLDCROWE]

.............and they all had bad batteries?

Thats why I replaced the batteries in both my 796's, both old but only one was HOT which was the original for the Cub unit

 

[Pete D]

I just saw this thread today and as I read through each update I was thinking battery...battery...

I've seen this back when we used the 396 and 496, loud static while the battery charged up. A new battery would fix the issue. Sounds like this is what you found on the 796 as well!

 

[OLDCROWE]

I just saw this thread today and as I read through each update I was thinking battery...battery...

I've seen this back when we used the 396 and 496, loud static while the battery charged up. A new battery would fix the issue. Sounds like this is what you found on the 796 as well!

I wondered about the charging but discarded it when the noise stayed in the Cub with the second 796 and battery (which I think was also bad but not making noise in my 180).