DSAB dropout - AP74 related?

[ChiefPilot]

Not sure if this goes here or the EFIS forum...

I recently finished installation of my EFIS-D10A, EMS-D10, AP74, and two SV32 AP servos.   Everything installed fine - I upgraded the firmware to 5.4 on everything and then configured the various pieces as needed.   So far so good!

The issue is that when I turn something else on, I lose DSAB communications - it doesn't matter if it's the strobes, pitot heat, avionics, landing light, etc.    I am running off just the battery at this point, but do have a bench power supply that supplies up to 5A @12V in addition to what the battery supplies.  

The problem does NOT happen if I do not have the AP74 plugged in - I can turn everything on and the everything functions normally (aside from the message about not being able to communicate to the AP74).      The EFIS still sees the EMS and servos without issue.   When the AP74 is plugged in and I power everything up, turning on anything else will cause the DSAB to disappear with the following symptoms :

1. All lights on the AP74 turn off
2. Communications between the EFIS and EMS is lost (no OAT reporting, etc.)
3. Messages about loss of communications on EFIS etc.


The problem remains until I power cycle the EFIS D10A; then it is ok.   It will not fix itself w/o powering down the EFIS and restarting.

Any suggestions?

Thanks!

 

[dynonsupport]

Chief,

I understand your last comment "The problem remains until I power cycle the EFIS D10A; then it is ok. It will not fix itself w/o powering down the EFIS and restarting."-- However, did you wait a full 90 seconds with no avail? If not, could you give it a try? Coincidentally, we are chasing a subtle DSAB error and your answer to this question would help me know if your situation falls into this category of error. Otherwise, we can look more specifically at the AP74, it could very well be a problem with that unit, but let me know on this question first.

Santa

 

[ChiefPilot]

Chief,

I understand your last comment "The problem remains until I power cycle the EFIS D10A; then it is ok. It will not fix itself w/o powering down the EFIS and restarting."-- However, did you wait a full 90 seconds with no avail? If not, could you give it a try? Coincidentally, we are chasing a subtle DSAB error and your answer to this question would help me know if your situation falls into this category of error. Otherwise, we can look more specifically at the AP74, it could very well be a problem with that unit, but let me know on this question first.

Santa

I will certainly check this out and time it for at least 90 seconds - thanks Santa!

 

[ChiefPilot]

I tried the test again tonight with similar results - I timed it for over two minutes and DSAB never came back. I believe I have identified a causal factor, however...

I have tied my AP74 to my audio panel to receive alerts as outlined in the "AP74 Electrical Installation" section of the manual on page 6-5 of the EFIS-D10A installation manual. The key factor here is that the audio line was just a length of 22awg wire; in fact, it was the same wire that came in the EFIS harness which I simply moved from the EFIS to the AP74 connector. I believe this wire was acting like an antenna, since I disconnected it and had no more issues with DSAB dropping out. I replaced it with a length of shielded wire, grounded at the audio panel, and the issue did not/does not appear.

If you'd like, I'd be happy to replace it with the unshielded wire if you'd like to gather data or investigate the issue further - I'll have good access behind the instrument panel for another couple of months.

Thanks!
-Brad Benson

 

[dynonsupport]

Brad,

Nice job narrowing it down to the audio line. I think I want to explore this a little more to try and get to the bottom of it fully. You pretty much have dealt with your issue, but since you are willing to try a couple more things that would be great, as it could help other folks out there. Could you email support@dynonavionics.com with your info and a reference to this thread and ask for the email to be forwarded to Nick. Then I will contact you directly and we can try a couple things.

Thanks for your help with this,

Nick

 

[ChiefPilot]

Hi Nick,

Done - thanks!

-Brad

 

[dodsond]

I am having a similar problem but I did't think much of it. I am in a hangar and when I transmit on my Comm 2 (an SL30) on higher frequencies, I get an audio feedback in the headset and my DSAB goes nuts. Sometimes I lose things and they come back, sometimes not until I cycle power to the EFIS.

I assumed it was antenna feedback from transmitting inside a metal hangar (near a corner even). The audio feedback had me a little worried. My HS34 is connected to the auido panel unswitched input with a reostat per the instructions. I will have to look to see if the wires are shielded, but I doubt it

I would like some follow up if there is a potential problem/solution.

I am not flying yet but I can test it outside in a week or two.

 

[ChiefPilot]

I am having a similar problem but I did't think much of it.  I am in a hangar and when I transmit on my Comm 2 (an SL30) on higher frequencies, I get an audio feedback in the headset and my DSAB goes nuts.  Sometimes I lose things and they come back, sometimes not until I cycle power to the EFIS.

I assumed it was antenna feedback from transmitting inside a metal hangar (near a corner even).  The audio feedback had me a little worried.  My HS34 is connected to the auido panel unswitched input with a reostat per the instructions.  I will have to look to see if the wires are shielded, but I doubt it

I would like some follow up if there is a potential problem/solution.

I am not flying yet but I can test it outside in a week or two.

I'm actually in the back corner of a metal hangar as well but transmitting hasn't been an issue for my project's system. By chance have you put a VSWR meter on your comm antenna from the point where it connects to the radio?

 

[dynonsupport]

dodsond,

See if you can figure out where the noise is coming from. You could disconnect the HS34 audio wire from the audio panel and see if the nose and DSAB issues are still there. Then we can narrow it down a little.

Nick

 

[dodsond]

I did a quick test the yesterday with the hangar door open and did not get the feedback, but that test was very brief.

I am nearly ready to fly and the airplane is all put together for its airworthiness inspection.  I don't really want to take it apart at this time.  So far, the problem was only on comm 2 so I can work around it if it persists when outside.  I will do some more checking in the next few weeks when I go some preliminary ground ops and check back in here.

My VSWR is not great, but not horrible either, FWIW.

Doug Dodson
Glasair II-S FT