Narco Mark 12-D - Open Mic Sound

[Skates97]

37 minutes ago, Andy95W said:

Sorry, Rich, I should have specified only volume on the headsets.

I'm thinking if pulling the squelch knob doesn't do anything, then it is probably malfunctioning and is now always on.  

Do you have a second radio, and does it happen to that one?  Or, if you actually turn the radio off, does the problem go away?  I think if you keep working on isolating the problem you will find it.

It does not happen on my second radio. If I turn the radio off the sound is gone, but when I turn it back on it is back. I know that should make it an issue with the radio, but after finding out that my wife is having a different symptom on her headset it made me think perhaps it is something to do with the intercom. I honestly don't know how the two radios are wired into the intercom but I am going to have a look the next time I get out to the hangar. At the very least I will check connections and also clean them with some contact cleaner.

[carusoam]

One of the challenges with Narco radios were the knob gears were made out of plastic.  They were sensitive to age.  The gear teeth fell off.

when you say the squelch function doesn't work and the knob that operates the squelch function doesn't work, I think you may have found the problem on that wonderful radio by that wonderful radio supplier...

Pull the radio...

1) try to look at the knob from the inside of the box...

2) if that is the problem, find a knob/gears that has been well taken care of...

3) find a different radio with a WAAS output...

4) I left a Narco radio at the company. They wanted $50 to inspect a broken gear on a tuning knob. Yeah, $50 bucks was a lot to me at the time... enough to remember and still be bitter about. 

5) sounds like you may be caught in the same trap...  fifty cent gears that make the radio work...

Good luck with your search...

Best regards,

-a-

Edited June 5, 2017 by carusoam

[Marauder]

It does not happen on my second radio. If I turn the radio off the sound is gone, but when I turn it back on it is back. I know that should make it an issue with the radio, but after finding out that my wife is having a different symptom on her headset it made me think perhaps it is something to do with the intercom. I honestly don't know how the two radios are wired into the intercom but I am going to have a look the next time I get out to the hangar. At the very least I will check connections and also clean them with some contact cleaner.

Another to look at is the connection in the rack. This was my Narco Mark 12D+'s issue.

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[Skates97]

Some success. I removed the radio and cleaned the connections on the back with electrical contact cleaner. I also did my best to clean the connections on the tray. After sliding it in and out of the tray a few times I checked it out. The squelch seems to work now and I flew for about 10 hours this past weekend without the usual problems of the open mic/squelch sound.

However, the wiring from the PTT to the intercom is possibly as old as the plane and very brittle feeling. I was going to replace it just to see if it would clean up the sound a little more. What gage wire is that and does it need to be shielded or unshielded? The stuff that is in there right now just looks like plain old 18 gage or close to that., maybe even 22 gage.

[Andy95W]

PTT wiring doesn't carry any amperage so you could use anything from 24 gauge and up.  18 is a bit thick for running through the yoke tube, and 24 may not last as long when it flexes with movement. 20 or 22 works well, just make sure it is good quality MilSpec wire.