Loose wire or something worse?

[skydvrboy]

I can no longer hear my #2 radio.  It worked when I left my home base and quit before I got to my destination with no hint at what was to come.  I have a KMA20 audio panel and the #2 radio is a KX125.  As I started testing, I found I can transmit, but not hear.  What is the likelihood that this is just a loose wire on the  KMA20?  That seems to me to be the most likely culprit. 

Additional testing I didn't think of doing would be to see if I can hear the Morse code on the Nav radio.  I'll test that tomorrow morning.  I'm pretty sure both the Nav and Comm audio come through the Comm channel on the KMA20.  If I can't hear the code, then I'm almost positive the problem lies with the audio panel and not the radio.

When I called a well known and highly regarded avionics shop, they wanted me to pull my radio and send it to them for testing.  I balked at that and asked them if they could instead get my whole plane in the shop to diagnose the problem.  I'm taking it to them tomorrow and will request that they inspect the KMA20 for a loose wire on pin 15 before they remove my #2 radio.

Anything else I'm missing here?  Other tests I should run to diagnose?  Questions I should ask the shop?

Edited October 5, 2021 by skydvrboy

[ArtVandelay]

I assume you tried a different headset and tried the copilot jacks?

[Yetti]

I've done that a couple of times and found that if I push the plug all the way into the jack it works better.    You should pull it out and push it in several times to clean the pins in the back.   Also swap one and two.

[skydvrboy]

1 hour ago, ArtVandelay said:

I assume you tried a different headset and tried the copilot jacks?

Actually, no, I didn't think of this since the #1 radio was working perfectly for both receive and transmit.  I'm not sure it's even possible for the headset or jack to be the problem, since there is a single audio out for the entire audio panel, but I'll give it a try.  It certainly can't hurt anything!  Thanks for the suggestion.

[ArtVandelay]

Actually, no, I didn't think of this since the #1 radio was working perfectly for both receive and transmit.  I'm not sure it's even possible for the headset or jack to be the problem, since there is a single audio out for the entire audio panel, but I'll give it a try.  It certainly can't hurt anything!  Thanks for the suggestion.

Good point. FYI, my audio panel has com and nav audio on different inputs (wires), so if both are silent I guess would suspect the radio.

[skydvrboy]

I’m at the avionics shop now. Five minutes in and they had the radio pulled and bench tested.  Dead audio out on the radio. Per the shop, the KX125 has a single audio out for both Nav and com. You listen to Nav by turning up the Nav volume on the radio.  I had both volumes at max, but when one’s dead, they’re both dead.

Edited October 5, 2021 by skydvrboy

[skydvrboy]

A leaking capacitor on the speaker output fried the circuit board. They’re going to change out the board and remaining old capacitors that are likely to leak and warranty the radio. I could probably get a used one for about the same price or a bit less, but the old capacitors in it would be just as likely to leak.

[LANCECASPER]

On 10/5/2021 at 9:11 AM, skydvrboy said:

A leaking capacitor on the speaker output fried the circuit board. They’re going to change out the board and remaining old capacitors that are likely to leak and warranty the radio. I could probably get a used one for about the same price or a bit less, but the old capacitors in it would be just as likely to leak.

Wow a radio shop that actually works on radios - very rare these days. Let me guess - the tech is over 60?

[skydvrboy]

2 hours ago, LANCECASPER said:

Wow a radio shop that actually works on radios - very rare these days. Let me guess - the tech is over 60?

If I had to guess, he was around 80. I kind of felt sorry for him working so late in life, but he genuinely looked like he was having fun.

[Marauder]

Wow a radio shop that actually works on radios - very rare these days. Let me guess - the tech is over 60?

A lot of the newer avionics are using wave solder technology for attaching components. Most of the older avionics can be serviced if it has through hole components and those components are available. And of course, the tech may need to use, heaven forbid, an oscilloscope to diagnose a problem.


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