push to talk won't transmit

[JoeM]

I'd appreciate any troubleshooting ideas....

When I push the copilot PTT switch (Two wires), I don't get a side tone, other aircraft / ATC can't hear me (I do not get "carrier no voice"), and there is no voice transmission through the intercom. The T light in each radio lights up and I do hear a click in the headset.

Have tried different headsets (all work on pilot side). PTT works. Both radios have same issue and work fine, including intercom, from pilot's side. Have tried intercom without PTT and copilot side doesn't work either. Have replaced PTT switch and confirmed it is working.

Equipment consists of 2 KX 155 TSOs, KMA 24 audio panel, Sigtronics SPA 400 TSO, and new wiring.

[Matt Ward]

I had a somewhat similar issue that was related to the wires behind the plugs not being grounded. Hard issue to diagnose but that was it after finally finding it!

[PT20J]

1 hour ago, Mooney79329 said:

, and new wiring

Well, I’d start there. Since the transmit lights on the radios work, the PTT and audio panel selector must be working. So, it must be a connection from the mic jack.

Skip

[JKeeth]

12 hours ago, Mooney79329 said:

When I push the copilot PTT switch (Two wires), I don't get a side tone, other aircraft / ATC can't hear me (I do not get "carrier no voice"), and there is no voice transmission through the intercom. The T light in each radio lights up and I do hear a click in the headset.

This might be a stupid question, but is the intercom switch in the ALL or CREW mode? If the intercom is in the ISO mode, then I believe what you are experiencing is normal, as only the pilot can transmit on the radios when the intercom is in ISO mode.

I'm in the process of troubleshooting a very similar issue with a Sigtronics SCI-4 intercom, but in my case transmitting from the copilot side works fine. I cannot however transmit from the pilot side when the intercom switch is in the ALL or CREW mode. The radios appear to be transmitting as the TX indication appears on both radios, but there is no voice heard on the receiving end. However, if the intercom is in ISO mode, then transmitting on the pilot side works correctly and sounds great, which tells me the wiring is okay from the pilot mic jack and PTT switch to the intercom, and from the intercom through the aux mic jack and to the audio panel. I'm leaning towards the intercom being defective, which was installed new a couple of weeks ago.

12 hours ago, Mooney79329 said:

Have tried intercom without PTT and copilot side doesn't work either.

Not sure what you mean by this statement. Can you elaborate?

Also, can you confirm the intercom audio is working normally at all seats? Pilot and passengers can hear copilot, and vice versa? If so, then that would indicate the wiring from the copilot mic jack to the intercom is good.

Jim K.

 

[JoeM]

Intercom question seems to be the right one so far. Will report after I test again with intercom in correct position.