Help with Garmin GMA245 and KX125

[infiniteaircenter]

Hello everyone, I am desperately seeking advice on wiring issue in a RV9A. I have the following:
- Garmin GMA245 audio panel connected to:
- IFD440 GPS/NAV/COMM
- King KX125 NAV/COMM

The issue is wiring for KX125 and it stems from this one pin 7 on the unit. I am not sure where it goes and/or connects to. From the schematics, it looks like it goes to the mic jack and some say it goes to aircraft ground. But I am not sure as IFD440's Mic Ground connects to Audio Lo on the GMA245.

Initially, I had pin 7 not connected to anything and the result was: When PTT is depressed, TX is visible on both GMA245 and KX125 but no audio is heard.

Then similar to IFD440's connection, I connected both pin 6 and pin 7 together to GMA245's COMM2 Audio Lo. The result was pretty much the same but now there is tremendous amount of static heard on test radio (not KX125 but a handheld unit) when I transmit.

At this point, I am about to connect pin 7 on KX125 to aircraft ground but wanted to seek advice beforehand.

So any advice/suggestion would be appreciated. Thank you

 

[vikbee]

Connect pin 7/P100 of KX125 to pin 10/P2401 of GMA245. Use two conductor shielded cable for wires connecting to pins 7/P100 and H/P100. Ground the shield at GMA245 side only. Isolate the shield at the KX125 side.

Of cause you can connect pin 7/P100 of KX125 directly to the airframe ground, but you can create a ground loop and pick up some noise. Mic signal is weak and is amplified quite a bit, together with the noise. Chasing the source of the noise later on might ruin your day ... or two ... or three ...

On a side note:
Mic key wire does not have to be shielded, so you can use a separate wire for that, but instead of the above mentioned two wire cable I usually use three wire one and use the third wire to connect pin 8/P100 of KX125 to pin 12/P2401 of GMA245. Just to avoid of using a separate wire for mic key. Up to you.

Vik

 

[infiniteaircenter]

Connect pin 7/P100 of KX125 to pin 10/P2401 of GMA245. Use two conductor shielded cable for wires connecting to pins 7/P100 and H/P100. Ground the shield at GMA245 side only. Isolate the shield at the KX125 side.

Of cause you can connect pin 7/P100 of KX125 directly to the airframe ground, but you can create a ground loop and pick up some noise. Mic signal is weak and is amplified quite a bit, together with the noise. Chasing the source of the noise later on might ruin your day ... or two ... or three ...

On a side note:
Mic key wire does not have to be shielded, so you can use a separate wire for that, but instead of the above mentioned two wire cable I usually use three wire one and use the third wire to connect pin 8/P100 of KX125 to pin 12/P2401 of GMA245. Just to avoid of using a separate wire for mic key. Up to you.

Vik

Thanks Vik! I will try that. Right now, I have it jumpered from Pin 6 to Pin 7 behind KX125 which made horrible static noise when transmitting.

 

[infiniteaircenter]

Connect pin 7/P100 of KX125 to pin 10/P2401 of GMA245. Use two conductor shielded cable for wires connecting to pins 7/P100 and H/P100. Ground the shield at GMA245 side only. Isolate the shield at the KX125 side.

Of cause you can connect pin 7/P100 of KX125 directly to the airframe ground, but you can create a ground loop and pick up some noise. Mic signal is weak and is amplified quite a bit, together with the noise. Chasing the source of the noise later on might ruin your day ... or two ... or three ...

On a side note:
Mic key wire does not have to be shielded, so you can use a separate wire for that, but instead of the above mentioned two wire cable I usually use three wire one and use the third wire to connect pin 8/P100 of KX125 to pin 12/P2401 of GMA245. Just to avoid of using a separate wire for mic key. Up to you.

Vik

Hi Vik,

Still not working. In the notes section for KX-125, it says to switch 2 wires. So does this mean that from GMA245 P2401 Pin 10, it should go to KX-125 P501 Pin 16?