RV12 Alarm sounds when PTT pressed

[richardsmi]

My RV12 and Dynon D180 have operated well for 100 hours in the UK.
I now have Exhaust temp alarms jumping to 1000deg+ figures when engine not running. This happened infrequently.
Now the problem has become serious because EVERY time I press the PTT to transmit the high exh temp alarm sounds and by the time you have hit the button to silence the alarm you have lost have half of your message, and communication with Air Traffic Controllers is very poor
Is there a simple fix?
I have checked the exhaust sensors and the wiring and can not find anything obviously wrong.???

 

[Dynon]

That sounds like a broken wire or EGT probe somewhere and it's acting as an antenna. Ignore the com thing for now, that's expected with an open wire that's getting RF energy. We'd recommend pulling the EGT, checking the probe, and then tracing the wires to see if the EGT is OK.

 

[richardsmi]

Thank you for that guidance I will certainly check that out.
May I ask a couple of questions to help my understanding:
a) If there is a broken wire associated with the EGT why did I get wild alarms before which went into the red range which did not seem to affect radio reception?
b) Wouldn't a broken wire affect the Comms all of the time and not be cured by pressing the alarm cancel buton?
c) If I can not find a broken wire is there a way in the Dynon set up that I can remove or isolate the EGT facility which will allow clear comms to be achieved.
d) Have there been similar reports where the Dynon has had to be returned to you the USA?
Best wishes Richard

 

[dynonsupport]

Ok, so there are two issues here:

1) The EGT reads 1,000 on the ground and changes when you press PTT. This is a broken wire going to the EGT. Thermocouple read random temperatures when they are open/not connected, and act like antennas for RF energy when they are like this.

2) Your radio transmission issue. We can't think at all what this would have to do with us. Sounds like a broken or weak antenna connection somehow. Having a broken antenna wire may make your EGT issue worse since a broken antenna connection can cause the COM radio to put most of it's energy inside the plane rather than transmitting it outside. This doesn't mean the Dynon is causing it, it's just reacting to getting a lot more RF energy than before.

If you are having the situation that the nose made by the alarm is the thing causing the poor reception, then that sounds like a mis-wired or broken intercom. The alarm noise should not have anything to do with your radio.

I think you need to look at the radio first, and get that fixed. I can't imagine it has anything to do with any Dynon equipment, unless somehow your radio antenna cable has become shorted to an EGT wire somewhere. Once the radio is fixed, then look for lose/broken EGT wires.

 

[richardsmi]

I don't feel we are singing off the same hymn sheet and it is probably because I have explained well enough the problem.
1.Without the Dynon the radio behaves properly.In fact the radio always functions well.
2 Having now checked the EGT wiring and security of the probes. I can confirm it is OK
3 For some time (last 20 hrs or so)I have had silly EGT readings which occur randomly but mainly on start up. For example one or the other EGT readings shoots up high when the engine has been only running for seconds and could not possibly have reached alarm temperatures. I generally ignore these and they settle down early in the flight . I can live with this.
4 The most recent effect is the pressing of the PTT actually "causes" the EGT to go into an immediate alarm state and it is the alarm sounding in my headset which kills sensible Comms with Air Traffic controllers. Stop transmitting and/or press he cancel button and the EGT returns to a normal / green level.
These symptoms do not seem to relate to a broken wire as the radio fuctions normally as so can the EGTs when they have done their "start up dance"
5. As an experiment I have set the EGT alarm to "Off" in an attempt to be able hear radio calls even if the EGT wants to jump araound but have not flown it yet.
6. What I would like to understand is "What is the link between pressing the PTT and the resultant instantanious EGT alarm condition?"

 

[dynonsupport]

The link between pressing PTT and the EGT alarm is that a lot of RF energy will cause incorrect EGT readings. They are very sensitive.

If it starts suddenly, this comes from one of two things:

1) Broken RF cabling, bad antenna ground, etc. This pumps a lot more of your radio power inside the plane rather than out.

2) Broken EGT wire. This makes the EGT into an antenna.

 

[richardsmi]

Thank you for your response on the 5th.
Since then I have:
Set the Dynon so that there is not an Alarm signal if the EGT goes over normal limits for what ever reason.
Went flying and carried out some radio checks
The radio worked perfectly. I made contact with two Airports one 40 miles away and the second 30 miles away. Radio checks with them was signal strength 5.

Pressing the PTT caused the EGT to fly upto high levels intermittently. Before,with the alarm sound on, it was every time the PTT was pressed.
So I now have a fully functioning radio as a result of eliminating the alarm noise and a EGT reading on the Dynon which is doing what it wants with no broken wires??

 

[TRCsmith]

This sounds like a problem I have. I have a portable APRS unit I fly with (inside the plane). When it sends out a burst of data it causes the EGT's and CHT's to jump into the red thus sending off the alarm (female voice).
In my case like you say, it puts all of it's energy inside the plane. So that is my problem not the skyview. Now I have noticed that pressing the mic button will cause the temps (EGT's CHT's) to move towards the max but it hasn't set of the alarm (female voice).
I have a Long EZ and my COM antenna is in the winglet approximately 11 feet from the EMS computer, but the com coax cable runs within a foot of the EMS computer. If that could be a problem just say "yep" no other explanation necessary. :

 

[dynonsupport]

TRCsmith,

We have a fix for SkyView systems where ALL thermocouples change with RF energy. Contact our support staff via email or phone, and we can update your EMS-220 module to get rid of this behavior. We will need it here to physically modify it.

This is only on SkyView systems, and only when all channels change, which is why this has not been referenced for the original poster who has a D180 and only one channel mis-behaving.