Registered Eric Greenwell Posted July 24, 2016 Registered Report Share Posted July 24, 2016 I just posted the following in the Dynon Skyview forum. I'm hoping someone here might recognize the symptoms and tell me how to fix it! -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- I have a Dynon com and intercom in my Phoenix U15 touring motorglider (Rotax 912 powered). Over the last couple of weeks, there's been an increasing amount of what sounds like ignition noise that gets worse (and higher frequency) at higher RPM in the air and on the ground. Originally, it was intermittent, but now is nearly all the time. The odd thing is the TX/RX labels in the lower right corner of the com radio display flicker rapidly when the noise occurs, and the LED on the intercom flickers a greenish orange. I haven't had anyone complain about spurious transmissions, but I haven't had anyone flying the times I began to realize it wasn't external interference, so I haven't asked anyone about it. Pressing either PTT switch gives a solid TX label, and solid orange on the intercom LED. It's been suggested there is a short in the PTT wiring, but I don't think the transmit function can be activated that rapidly: the flickering of the TX/RX labels is several times a second, and the noise on the order of 1 kHz. The situation exists even with all other devices, including Skyview, shut off. I flew the plane for 2.5 years and 300+ hours before this noise appeared, so I think the original installation (professionally done by people that have done identical installations in 10+ Phoenix) was done correctly and something has changed - but what? Quote Link to comment Share on other sites More sharing options...
edwalker Posted July 24, 2016 Report Share Posted July 24, 2016 Hi, Eric - It does seem puzzling that this should appear after so many hours of trouble-free operation. I have one observation, but not sure it's relevant. I bought a GoPro camera last year and have enjoyed using it. It has a microphone, but I wanted to patch in the radio audio, so I bought an audio adapter from Nflightcam which picks off the headset signal and also has a USB power cord to keep the camera battery fresh. It states very clearly that you cannot use it with a USB adapter connected to the aircraft 12v bus, and they recommend a few USB battery packs. Of course, it was irresistible to test this so I could experience the problem they were trying to avoid. The camera will work well with the cord, and the audio is crystal clear as long as you don't use aircraft power. You can also use aircraft power and not use the audio, allowing the camera mic to pick up the cockpit sounds (which is not too bad in soaring mode). But when you use both with the engine running the subsequent ground loop is full of RPM-dependent noise similar to what you are describing. I first hoped I could use an audio transformer to diminish this, but it didn't seem to make a difference, so I had to conclude that the aircraft DC is very dirty, and that's hard to clean up without very expensive opto-isolator-based DC power conditioners, so ground loops are tough to eliminate. The only final solution seemed to be to use either the audio cable OR the USB power outlet but not both (although an external USB battery source was fine). This makes me wonder if something similar has developed in your plane. Did you try disconnecting the video camera from the Dynon adapter? That's the only possible ground loop I can think of from what I know about specific modifications you've made to your plane. Are you running any additional equipment directly off your paxbatt that could put RF into the local environment? If none of this is true, I guess you just have to pull the plugs on the radio, intercom and SV and test for ground pin continuity. Maybe a pin has shaken loose? Good luck...hope you find the source. Ed Quote Link to comment Share on other sites More sharing options...
Registered Eric Greenwell Posted July 24, 2016 Author Registered Report Share Posted July 24, 2016 2 hours ago, edwalker said: Did you try disconnecting the video camera from the Dynon adapter? I removed the video camera a few days before the noise got so bad; however, the cords for it still extend into the engine compartment and may be picking up engine noise. Tomorrow, I'll disconnect the video adapter, or shield the open end of the video cable on the engine side of the firewall. The camera was removed because it became intermittent (connector bad on one end), and because I want to replace with with a 50 to 70 degree field of view (the Bosch I was using is 95+). Quote Link to comment Share on other sites More sharing options...
edwalker Posted July 25, 2016 Report Share Posted July 25, 2016 One other idea. Pull the seat pans and inspect the PTT switch wiring on both sides from the switch all the way to the connector for abrasive wear as far as you can and check the resistance of the circuit at the connector pins as you move the controls. The stick is moving a lot, so the wire has to flex somewhere, and it's possible that the insulation is wearing and allowing an intermittent short. Quote Link to comment Share on other sites More sharing options...
Randy Roth Posted July 25, 2016 Report Share Posted July 25, 2016 Hello Eric, Ed and All, Just wondering if a simple solution such as adjusting the squelch setting on the radio could help? The Dynon radio manual discusses setting squelch. Perhaps it inadvertently was changed. Otherwise, chasing down a loose ground or the unshielded additional wires sounds like the way to proceed. Personally, I would go after the new camera end plug first. Good Luck, Randy Quote Link to comment Share on other sites More sharing options...
Registered Eric Greenwell Posted July 25, 2016 Author Registered Report Share Posted July 25, 2016 I shielded the open ends of the video cables in the engine compartment, but the difference was barely noticeable. I disconnected the video adapter's USB cable from the Skyview monitor, and that reduced the noise by about half (almost tolerable). My next thought is removing the video cables entirely. Looking through my notes, I see I was experiencing the static a couple months ago, though intermittently and with less volume, and usually near clouds. Not a clue about that. I also remember the radio having some issue while I was in Florida in 2014, getting flight training from Jim. He moved a couple cables around behind the right panel, and that seemed to cure it. I'll check that area for changes, and check the squelch, too. Quote Link to comment Share on other sites More sharing options...
Thermalseeker Posted July 30, 2016 Report Share Posted July 30, 2016 It sounds to me like you have an intermittent grounding issue. Check every mechanical ground connection in the audio system. This is why I always solder audio connections. Could be in the intercom shielding, intercom ground wiring, or chassis grounding of the intercom or radio. Although less likely, it could also be in the main ground buss wiring. Could be a loose connection, or something that is beginning to corrode. Doesn't take much at audio line levels. Quote Link to comment Share on other sites More sharing options...
Registered Eric Greenwell Posted July 31, 2016 Author Registered Report Share Posted July 31, 2016 When I turned on the transceiver and intercom today, the "TX" symbol appeared, and the intercom LED turned orange. I removed the power from the transceiver (removed it's fuse), but the intercom LED remained orange. I removed the right panel so I could easily reach the cable going to the intercom; wiggling the cable gently caused the intercom LED to blink green and orange. I disconnected the cable, then measured the PTT microphone inputs on the connector; unfortunately, both read "open". I plugged it into the intercom, but everything was working normally now. All the wiggling, pulling, and tapping I did never caused the TX symbol to appear or the intercom LED to change from green to orange; apparently, the short (wherever it is) has "fixed" itself. I put everything back together, then added a ty-wrap to support the cable better, as it was hanging from connector previously. I'm closing in on the source of the problem, I think, but will have to wait for the problem to appear again, as I don't want to tear in to the four microphone "transmit" lines (two PTT, and two from the pilot and co-pilot headset jacks), looking for a solder joint or ? that is rubbing against the other lead. Quote Link to comment Share on other sites More sharing options...
Thermalseeker Posted July 31, 2016 Report Share Posted July 31, 2016 Try wiggling the suspected wires and connectors in the dark with the system energized. You may see a slight flash of light as the short makes and breaks that will point you to the source of the problem. Could be a broken wire, cold soldered joint, worn spot, etc. If the intercom/radio uses D-sub style connectors look for a male side pin that has pushed back. I've seen that one a bunch. Quote Link to comment Share on other sites More sharing options...
tim wilson Posted January 26, 2017 Report Share Posted January 26, 2017 Eric did you resolve the engine noise/TX problem?. I also had an intermittant, then constant, engine rpm noise caused by induced EMF via a broken power line to my Garmin. Jim's troubleshooting of moving wires to try to determine where the open/short is a pretty darned good technique.. Good luck on solving. Quote Link to comment Share on other sites More sharing options...
Registered Eric Greenwell Posted January 30, 2017 Author Registered Report Share Posted January 30, 2017 On 1/26/2017 at 10:26 AM, tim wilson said: Eric did you resolve the engine noise/TX problem?. I also had an intermittant, then constant, engine rpm noise caused by induced EMF via a broken power line to my Garmin. Jim's troubleshooting of moving wires to try to determine where the open/short is a pretty darned good technique.. Good luck on solving. I haven't had any noise since July 30, 2016, when I removed and replaced the connector on the intercom panel. That's about 50 hours of operation. Quote Link to comment Share on other sites More sharing options...
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