Odd headset puzzle

[fernytickles]

Has anyone ever come across this problem....not personally experienced, but explained to me second hand.

Cessna 560, Telex 850 headsets.
Plug in both 850s and both comm 1 & comm 2 become live, intermittently, on the headsets.

Cessna mechanic said "headsets are powered through the avionics, which is what causes both comms to become live at the same time".

I'd never heard of this problem, but I haven't been around aviation since it first started and was interested to hear if anyone else has experienced this.

[Taxi2parking]

I'm fairly sure we had a similar issue on some of theExcels in our company using telex headsets....

[JRBarrett]

Are you saying that you are receiving incoming transmissions from both COM radios, even if only one of the two COMs is selected on the audio panel?

The fact that the headset is "powered by the mic jack" shouldn't have any bearing on the issue. That simply means that the noise reduction circuitry in the headset takes its power from the voltage on the microphone line in the jack. (Typically about 5 volts).

Do the aircraft's audio panels have an "auto" button? If those are depressed on either or both audio panels, it is possible to receive on both radios, even if only one is selected to receive.

Another possibility: the Telex 850 can operate in stereo IF the jack in the aircraft is wired for discrete left and right channels. If the jacks are wired in mono, (as is typical), that may have something to do with the problem. If the headset plug isn't seated quite right in the aircraft headphone jack, it could be bridging receive audio from one side over to the other via the intercom. If the headset or line cord has a "stereo/mono" switch, be sure its set to "mono" on both headsets.

Jim Barrett (Avionics Tech)