Need PTT help- PMA-4000

[sgfreeman]

PMA-4000 with Garmin GNS-300XL GPS/Com (both installed) and SL-30 (tray and harness installed but SL-30 itself not installed). Stark Avionics did the wire harness for all avionics.

Two problems that may be related:
1) When I power up the PMA-4000 and GNS-300, the lighted Com1 and Com2 push buttons are steady. When I press the PTT button they flash as stated in PMA-4000 documentation. When I plug my Mic jack in (Peltor 7004) both the 4000 and 300 show transmit without the PTT button depressed. I have verified the wiring between the mic jacks and PTT button several times-it is per the PS Engineering Schematic and continuity checks show the wires are correct to the Mic Jack. I can pull the mic jack PTT connector away from the Headset plug and the transmit mode stops until I press the PTT button again.
I can't figure out why the PTT circuit closes when I plug the headset in and it makes contact with all three jack connectors. It behaves like the sleeve and PTT tip are connected within the headset. I can hear the "click" when I depress the PPT button both when the headset Mic is plugged in and when it is not.
2) I cannot hear myself talk thorugh the headset in any scenerio.

Any help would be very much appreciated.

This is getting frustrating.

Thanks.

 

[L.Adamson]

I'm looking at my PMA 8000B wiring diagram, and haven't thought it all through...

But are your mic/headphone jacks totally isolated from the panel with isolating washers; so they don't ground out?

L.Adamson

 

[LOGGY]

ground

double check the tip .....it sounds like your grounding ..........do you have a handheld radio to check if you are transmitting?

 

[sgfreeman]

Yes, I have insulating washers and have verified the jacks are not grounding out. Also, just to make sure, I removed the jacks from their mounting holes (just suspended in air by the wires) and the problem still exists. I do have a handheld and will try to validate if I am transmitting tonight- thanks for the suggestion.

 

[647jc]

Maybe an obvious question but are you sure you have wired the small jack for the MIC and the large jack for Headphone?

 

[sgfreeman]

Joe,
I feel like a real dummy. You hit the nail on the head. I have a handheld with adapters for my headset. The adapters on the small end that go into the handheld have a larger plug for the mic and smaller for the phones- opposite of the full size plugs. I just assumed the larger plug on the headphones was the mic also. Embarassing to admit, but I really did do it. Thanks for the help. I ordered new jacks and will try again. I guess one good thing came of it, I did continuity checks on all my connectors all the way to the audio panel and everything checks out.

Thanks again and you will have a good story for some hanger laughs....you won't believe what this one guy did.....

Scott

 

[647jc]

Scott,

Glad I could help. That was about the only scenario I could imagine that would result in what you were describing. Don't feel too bad about the mistake, we ALL and I mean ALL have made similar mistakes and will probably make more in the future.

 

[noelf]

I went through the same thing just last week...

...my setup is Garmin audio panel, SL30, SL40, txponder, and GPS...all individual units.

Powered up the audio panel, and the 2 coms...Sigtronics headset in pilots side mic and headphone jacks. As soon as the the SL30 (com 1) was powered on, it went to transmit mode, and 30seconds later the stuck mic LED came on.

Tried the SL40 (com 2) and the same thing happened. Tried plugging into the passenger side jacks, and the same symptoms as before were observed. The headphones were pure noise/ static, and I was unable to adjust the volume down.

Lots of trouble shooting later, I "discovered" that the Sigtronics mic plug (3 contacts, .206in diameter) was constructed different than the plug on my David Clark headset mic plug. The DC plug was the true PL-068 style that mated exactly to the jacks installed in the aircraft. When compared to the Sigtronics plug, the overall length dimensions were different.

The Sigtronics mic plug uses a "commercial" version of the plug as compared to the DC's. The Sigtronics version contained a rubber over mold around the plug/wire connections, and this molding continued to include the "face" of the mic plug. This prevented the plug from seating all the way into the the jack, with the result that the Sig plug Ring and Sleeve contacts were shorted together by the contact position detents on the jacks.

I spent some internet time trying to find out if the jacks or the plugs were out of spec, and why the DC vs the Sig's were different. I checked out the Switchcraft website, as well as some others, and only overall dimensions are given. But the real shocker is an abstract to a report by the Audio Engineering Society, Inc (report # AES-R3_2001) that describes a paper which expresses a concern that there are no "standards" which give the detailed dimensions for the TRS (tip, ring, sleeve) type of jacks and plugs used in the industry. One manufacturer may have invented one set of dimensions, and it may not be the same as a second manufacturer.

My DC mic plug has a different length dimension than the Sig.
The DC has plug detents in the tip and ring areas, the Sig has a detent only in the tip area.
The physical location of the plug "ring" area is noticeably different between the two headset types, with the result that the Sig unit is not compatible to the jacks (ACS p/n JJ-033) as installed in my aircraft.

Bottom line...using the David Clark headsets cleared up my stuck mic problems.