Intercom problem

[Taltruda]

I’ve got a weird problem with my intercom or radio, not sure which one is the offender. It’sa PM1000 II intercom with an Icom IC-a200 radio. All works normally when I first turn on the avionics switch. However once I transmit, my back seater cannot hear me, and I have to turn off- then on the intercom to restore the intercom function. (I can still hear the intercom from the back seater). Here’s where it gets weird, When I turn off the intercom, the radio becomes “Hot” meaning it’s transmitting. I have verified this by turning off the intercom and speaking to ATC. Any suggestions on where to start? Thanks in advance!

 

[BobTurner]

Your intercom has a ‘fail-safe mode’, where the pilot’s headset including PTT are routed, via a relay turning off, directly to your com. That’s why you can talk to ATC with the intercom off. I’d be looking for some weird internal failure on the pilot PTT line, where once the PTT is pushed the line hangs up at ground voltage, even after the switch is released, until you cycle power. A voltmeter on the PTT line should confirm or refute this idea.

 

[blaplante]

more debug

Can he hear you when you do that initial transmission?
How about a subsequent transmission?

Some of those ICom's have an internal intercom function. Doubt that is the problem, but make sure it is turned off.

 

[Taltruda]

My back seater can hear me when I transmit on the radio, but can’t hear me on the intercom after the first tx. I can hear the back seater though. When I shut the intercom and my radio goes to full time TX, the rear seater can’t hear my transmission.

 

[BobTurner]

When I shut the intercom and my radio goes to full time TX, the rear seater can’t hear my transmission.

This part is how it should be. With the intercom powered off, a relay should drop and connect the pilot (but only the pilot) directly to the radio. Back seater won't hear anything, nor will you hear him. But why the PTT circuit seems stuck "on" but only after the first transmission, that's the mystery. You could try contacting the guys at PS, they might have an idea.