Rice Crispies sound coming from Skyview screens

[jaredyates]

I've tried searching the archives but haven't found any good resolution to the noise issues. In my audio system I'm getting a slight but noticeable "snap crackle and pop" in my headset, over the intercom. When I turn of the SV displays the sound goes away. I've been living with it for a while, but having just installed a new intercom and finding that the sound is the same, I'd like to try and do away with it. Any suggestions on how?

 

[n456ts]

Those sounds can often be associated with a poorly made/loose connection. Do you have any butt-connectors in your audio circuits?

 

[preid]

funny! I get noise when the displays boot up, than the noise goes away once the screen is booted.
Sounds like a short to me.

 

[jaredyates]

Thanks for the input.

n456ts, Yes, I do have butt connectors in the audio system.

Reidaviator, What conductors would the short be between?

 

[DHeal]

Such noises can also be generated by the microphone of a plugged-in / unused headset banging against something thus momentarily activating the mic circuit. Unplug all unused headsets and see if the issue goes away.

 

[jaredyates]

Yes, thanks, that is done. Also, the noise comes and goes when I power on and off the screens, and it sounds different than that sort of microphone noise over the intercom.

 

[mmarien]

Do you get the same sounds with a handheld?

 

[jaredyates]

The sounds are on the intercom, not sure what you mean?

 

[n456ts]

I would remove those butt connectors and fix those bad connections.  Poorly made connections are going to be the cause of your noise.  And from your other post on your auto pilot, I would suspect the same for it.

 

[jaredyates]

Your input regarding your personal preference to not use butt connectors is noted, thank you. We do not agree on this issue, and as such, it is certainly acceptable for you to not spend any of your time helping me actually mitigate the problem. While I would prefer that you not, you are free to blame any maladies that I might experience on my choice to use butt connectors, up to and including the accumulation of dead bugs on the windscreen. This is, naturally, not any help, but I do appreciate the attempt.

There have been plenty of online discussions about the preference for wire connection methods, so there's not much point in rehashing them here. I continue to welcome actionable troubleshooting advice on the noise issue.

Considering the suggestion that the noise is coming from a "poorly made connection," regardless of the connection method... If an intermittent connection was the problem, why would the noise be so consistent and repeatable? It happens every time, all the time, the same way. When the screen is on, the noise is on. When the screen is off, the noise is off. If the connection was poorly made, then I'm not sure about why the audio output would otherwise be working correctly. If I'm missing something here, I'm counting on someone to point it out...

 

[mrdaud]

Jared, not commenting on if your connectors are the problem or to get off subject, but being old school and military trained in avionics, the use of butt connectors, in general, should be avoided when possible. We were not allowed to use them in our military avionics applications. I personally do not have one butt connector in my airplane. All permanent connections were solder connected, and removable connection were made with Amp, Molex or other mil spec connectors. Many problems with butt connectors are due to people using cheap connectors and crimping them with wire stripper/crimper pliers. If you absolutely determined to use butt connectors, use mil spec grade splices and mil spec crimping tools. This is also the case with spade and ring connectors. I, of course use those, and occasionally still find a bad ground or power connection at the connector even though I use a mil spec crimper. Of course, you know what they say about opinions!

 

[jaredyates]

Thank you, all of my splices are name-brand AMP PIDG part number 320559, applied with a ratcheting crimper. Any connection method is susceptible to poor craftsmanship, and while I'd never say that all of mine are perfect, I will say that considerable effort is applied to ensuring good connections.

 

[n456ts]

No one here designed or built your system.  Everyone's setup is different.  It's not clear how many skyview screens you have, nor much else about your configuration.  You could have a ground loop somewhere, however, your issue sounds different.  More data would be helpful including what troubleshooting have you done at this point.  Do you have available the schematic of the system you designed for your aircraft? 
Did you try isolating the different parts of the system and check for a condition change?  Example:  If dual screens, systematically removing the audio output pins of each screen.  Checking for any state change, pre/post pin removal.  All shields grounded only at one end and bonded to a non-current carrying ground? 

Until everyone owns an internet connected robot that can operate a DVOM, we can't perform the basic troubleshooting via a keyboard. 

 

[jaredyates]

I would say that I've primarily come here to try an establish a good troubleshooting strategy, and appreciate the help in doing that. So far my troubleshooting has been limited to isolating the components by powering them down one at a time, but if removing the audio wires from each screen will be informative, I can certainly try that too.
The components that touch the audio system include two 7" Skyview screens and a PS Engineering PAR100EX audio panel with its own intercom (the problem also persisted with a PM3000 that I recently removed to install the PAR100EX).
There other items that connect to the audio panel like the GNS430W and headset jacks. I can elaborate on those if it helps, but the target sound only appears when the Skyview screens are powered on, and it never appears when the screens are powered off.
The audio cables from the Dynon screens to the audio panel are not shielded. The installation instructions (page 4-25 on the version that I had handy) say this:
To minimize the possibility of audio “humming”, a 16 AWG wire may optionally be connected between the ground point for the intercom/audio panel/radio(s) and SkyView display case(s). To attach the wire to the SkyView display case, a 4-40 x 3/16” long screw may be screwed into the threaded boss above the USB ports on the back of the SkyView display.
I have not yet done this, but I can include it as a troubleshooting step. All of the units are installed in a single aluminum instrument panel.
Here is how it is currently wired:
Skyview Pin 30 (audio ground) on the left screen is connected to the same pin on the right screen. Same with Pin 31 and 13. Pin 31 and 13 (left and right skyview audio out) are then connected together, and then that goes into pin 31 (unswitched mono audio in) on the intercom/AP. The combined left and right Skyview pin 30 (audio ground) are connected to pin 32 on the intercom, which is the audio low for the unswitched input.

Let me know if any more detail might help. There are other Dynon components but I haven't listed them since only the screens go to the audio system.

 

[mmarien]

The sounds are on the intercom, not sure what you mean?

If the handheld picks up the same rice crispies sounds then it narrows it down to a problem with the SV installation. If not then I would look at the intercom/radio for the problem.

Turning on SV introduces the noise but it also could be a ground loop in the radio/intercom wiring causing the problem. In other word, SV could be grounding through the intercom so the problem only appears when SV is on. Ground SV directly to the battery to see if that changes anything.

 

[jaredyates]

I'm not following what you mean, can you use more words please? Are we talking about a handheld VHF radio? Are we trying to determine if the sound is transmitted over the radio when the pilot keys the PTT? On the intercom, the sound is pretty quiet, I'm not sure that it would be discernible above the usual noises one hears on the VHF transmission.

As for testing by grounding the SV directly to the battery, is that in addition to the grounds that are currently in the system, or separate from them, and are you talking about grounding the SV case, pin 21/22, etc?

 

[mmarien]

I'm just trying to determine where the noise is coming from. When you turn on SV you say you are getting crackling noise through the intercom. If the noise is generated by SV then it will also affect any radio near SV. So get a VHF handheld radio, hold it near SV and turn on SV. If there is no crackling noise generated on the handheld then the problem probably isn't SV.

How are you doing your grounding? Do all grounds run back to a grounding bar, or are you grounding things to the frame?

If SV isn't creating noise on the handheld, then it's coming from somewhere else. Probably the wiring. I'm suggesting a ground loop may be causing the problem. The noise appears when you turn SV on. If SV is finding it's ground through the intercom, then it will cause lots of noise on the intercom. To try and isolate the problem, disconnect the two SV ground wires from where you have them grounded and ground them directly to the battery. Then check to see if the noise is still there.