I'm posting this in the Audio Panel space because it's the only hardware common to both radios.  Read my story and let me know if I need to call for an exorcism.

I was flying about 1000 nm last week (yes, home from OSH) and at least half a dozen times I lost the ability to hear incoming comm on BOTH radios!  It happened while with Chicago center, Minneapolis center, Kansas City center, and Fort Worth center; I don't think there were all having transmission issues on the same day.  Here's what I know -

1. All would be quiet and I would get an urgent call from either center or another airplane center had pressed into service to help contact me.  When I would answer I could always hear fine and the transmissions from other aircraft and center with both strong and clear.

2. Other times it was the reverse, things would be quiet and I would key up for a radio check.  Two or three calls later I would hear the response and they would always tell me they heard every request and responded each time.  I only heard after several responses.

3. I switched to my backup radio and had the same thing happen!

4. At one point I turned an ATIS freq that was nearby and monitored.  Things were fine for a while and then the transmission stopped.  The RX indicator on the 540 was not lit.  When ATIS was again audible it was the same broadcast as before.  The time was not the appropriate time for a change to ATIS.

5. While I do not believe my airplane was hit by lightening, it was parked in the North 40 at OSH all during the week and there were a few strong storms that passed near the area.  Heavy rain and strong winds were common and a few rumbles of thunder.  I don't camp at the airplane so I wouldn't know how it was at that exact spot during the storms.

As far as I know now there are no common parts between the radios other than the 240 audio panel.  However, that should not inhibit the RX light on the 540 even if it blocked the audio from coming through.  Also, my with was with me and we could always talk to each other - which was easy in times of silent radios!

Lastly, being a long trip I brought an MP3 player and plugged it in through a music input jack through the 540.  The music never stopped playing (I pressed the 'music' button on the 240 so the music doesn't mute during radio transmissions) so I know there wasn't a loss of all sound.

 

Did your avionics guy, who did the install, wire up the interlock to mute the receivers in the other one is transmitting? If so, I would pull that wire out and see what happens. 

Tony, the install was done over a year ago with no issues until the last flight so I don't think it would be an incorrect wiring.  If it were it would happen all the time.

Like you I don't believe it could be the audio panel but I posted here because that's the only common piece between the two radios.  Otherwise all systems are separate including antenna and wiring.  Just strange to have them both act the same wrong way at the same time.