PTT circuit

[jsstevens]

I replaced the cable on a Gulf Coast Avionics GCA-4T headset. It's a simple mono headset with no PTT. I copied the wiring colors. Upon testing the headset works except the mic intermittently sticks open (as if the PTT is being held down).

According to the diagrams I've found, the PTT shorts the tip and sleeve on the mic plug. I've got an AVCOMM headset with a PTT built into the earcup. I put my ohm meter on the tip and sleeve and pushed the PTT expecting to read a short. Nope, all open. I've ohmed the tip & sleeve on the GCA and it seems to be solidly open.

What am I missing?

John

 

[yetti]

The "short" is to ground of the airframe. The PTT NO switch just completes the circuit when closed.

 

[bluerooster]

Yes, if the sleeve is isolated from earth then you get no connection. What the PTT does is provide a ground path to complete a circuit.

 

[jsstevens]

So if I put an ohm meter across the sleeve and tip of the mic plug, then push the button on the headset I should read a short? This would be "providing a ground path to complete the circuit", correct?

John

 

[bnt83]

So if I put an ohm meter across the sleeve and tip of the mic plug, then push the button on the headset I should read a short? This would be "providing a ground path to complete the circuit", correct?

John

Yep

 

[jsstevens]

OK, but when I did that, I didn't get a short. Of course, I've never tried to use the PTT on that headset because all the planes I've been in had PTT on the yoke. So maybe it's broken. Hmm.

At any rate, it seems I'm looking for an intermittent short on the repaired headset, which is what I suspected from the beginning.

John

 

[yetti]

So if I put an ohm meter across the sleeve and tip of the mic plug, then push the button on the headset I should read a short? This would be "providing a ground path to complete the circuit", correct?

Maybe. A PS Audio panel has instructions to modify various headsets to work with their panels. With PTT on the yoke it is wired from a pin on the audio panel to the NO switch then to airframe ground

 

[weirdjim]

So if I put an ohm meter across the sleeve and tip of the mic plug, then push the button on the headset I should read a short? This would be "providing a ground path to complete the circuit", correct?

John

No. You were correct in your first comment that the PTT switch shorts the SLEEVE to the RING, not the tip. The SLEEVE (the long metal shaft at the bottom of the metal plug) is normally connected in the aircraft through the headset jack to airframe ground. The PTT switch IN THE AIRPLANE then shorts the RING to airframe ground through the SLEEVE. If someone can tell me how to SIMPLY post an image to this board, I'll be happy to post a picture out of our instruction manual for the headset.

Don't worry about what it does in the airplane. Test the headset all by itself without worrying about how the airplane is wired.

If you've got an ohmmeter, then you've got a voltmeter and a milliammeter as well in a multimeter. We can use a 9 volt battery and 1k resistor (if you can lay your hands on these) to test the microphone circuit as well. Get back to this board on whether the PTT on the headset does in fact short sleeve to ring.

Pictorially --- ======sleeve====== - ==ring== - =tip=>

Jim

 

[jsstevens]

No. You were correct in your first comment that the PTT switch shorts the SLEEVE to the RING, not the tip. The SLEEVE (the long metal shaft at the bottom of the metal plug) is normally connected in the aircraft through the headset jack to airframe ground. The PTT switch IN THE AIRPLANE then shorts the RING to airframe ground through the SLEEVE. If someone can tell me how to SIMPLY post an image to this board, I'll be happy to post a picture out of our instruction manual for the headset.

Don't worry about what it does in the airplane. Test the headset all by itself without worrying about how the airplane is wired.

If you've got an ohmmeter, then you've got a voltmeter and a milliammeter as well in a multimeter. We can use a 9 volt battery and 1k resistor (if you can lay your hands on these) to test the microphone circuit as well. Get back to this board on whether the PTT on the headset does in fact short sleeve to ring.

Pictorially --- ======sleeve====== - ==ring== - =tip=>

Jim

Thanks Jim. I'll test that this weekend.

 

[denverpilot]

If someone can tell me how to SIMPLY post an image to this board, I'll be happy to post a picture out of our instruction manual for the headset.

You create the image and simply drag and drop it from your file browser onto the browser edit box for your post. It'll upload it and ask you right below the edit box whether you want full sized or a thumbnail.

 

[bnt83]

PTTs that I have wired pull the tip to ground. If a PTT contained in a headset does different, it won't work.