Radio Trouble

OkieFlyer

OkieFlyer

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May 16, 2011
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3,225
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Lindsay, OK
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Display name:
Andrew L.
Went up this evening to enjoy the beautiful sky, and wound up having radio issues. I can't hear anything coming in! Intercom works fine, but I was unable to hear atis, and when I press the PTT, I couldn't hear myself. I spoke to a friend who was also out flying, and he said I was transmitting loud and clear. I could not hear his transmissions. Also, when I let go of the PTT, I could hear the little momentary fuzz noise (if that makes sense. Typical radio noise). It's an old Narco 120, and the T symbol was lighting up when I keyed up. Any idea what may cause that?
 
I would try a different headset before I had an avionics shop have a look at the radio itself.
 
I was thinking bad headset or corroded headset plugin. Try another headset or take the headset off and try the speaker. Or, maybe just check to be sure the intercom isn't set to speaker instead of headset. I have had that happen before by accidentally bumping the switch.
 
Turn the volume up, correct switches on the audio panel. Try another set up plug in location, different headset
 
Thanks guys. I did try a different headset, tried two different headsets in different jacks (pilot main, pilot aux, and copilot), messed with volume and squelch on both the radio and intercom, tried it on speaker, cycled all the switches, and basically fiddled with everything that will move on the radio, audio panel, intercom, and headsets.

I need to correct myself from the original post: The radio is Narco MK-12d. Narco CP-136 comm panel.
 
OkieFlyer said:
Thanks guys. I did try a different headset, tried two different headsets in different jacks (pilot main, pilot aux, and copilot), messed with volume and squelch on both the radio and intercom, tried it on speaker, cycled all the switches, and basically fiddled with everything that will move on the radio, audio panel, intercom, and headsets.

I need to correct myself from the original post: The radio is Narco MK-12d. Narco CP-136 comm panel.
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So what I am hearing is that there is no way, whether it be speaker or headphones that you can get com audio? I can't remember whether the CP136 has a "bypass" switch that lets you hardwire the radio directly to the speaker and phones. I don't believe that it did. How much diddling under the panel are you willing to do? Any test equipment at all?

Jim
 
weirdjim said:
So what I am hearing is that there is no way, whether it be speaker or headphones that you can get com audio? I can't remember whether the CP136 has a "bypass" switch that lets you hardwire the radio directly to the speaker and phones. I don't believe that it did. How much diddling under the panel are you willing to do? Any test equipment at all?

Jim
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Correct. No audio whatsoever from the radio.

I am willing to do whatever I need to do under the panel. I ain't skeerd, but I'm not terribly proficient at such things. I actually plan on moving my nav/comm and transponder down on the panel and moving my GPS up to the top, so I'm going to have to dig in anyway.

I currently have a multimeter, that's about it as far as test equipment.
 
weirdjim said:
Just curious. If the intercom was working, which implies that both his microphone and his earphone on his headset was working how it could be the headset?

Jim
Click to expand...
When it comes to things I am ignorant about I try what is easy first.
It is easy to try a different headset.
I have found that aviation radios and intercoms tend to be quirky so I would take it to someone who knows about such things next rather than trying to fix it myself.
I have found the interface between my radio and intercom particularly confusing.
I am not saying that is what he should do, that is what I would do based on my experience.
 
Vance Breese said:
When it comes to things I am ignorant about I try what is easy first.
It is easy to try a different headset.
I have found that aviation radios and intercoms tend to be quirky so I would take it to someone who knows about such things next rather than trying to fix it myself.
I have found the interface between my radio and intercom particularly confusing.
I am not saying that is what he should do, that is what I would do based on my experience.
Click to expand...

No worries, man. He's right that the headset is basically proven to not be the problem by working fine over the intercom. I knew that from the get go myself, but I still tried switching headsets. Got to eliminate even the most unlikely of causes. Thank you.
 
OkieFlyer said:
Correct. No audio whatsoever from the radio.

I am willing to do whatever I need to do under the panel. I ain't skeerd, but I'm not terribly proficient at such things. I actually plan on moving my nav/comm and transponder down on the panel and moving my GPS up to the top, so I'm going to have to dig in anyway.

I currently have a multimeter, that's about it as far as test equipment.
Click to expand...

OK, if you are going to be digging in anyway ... go to Radio Shack and get a quarter-inch phone jack. Stereo if you have to, but mono is easier. Take foot or two of 2 cheap wires and solder one end to the tip and sleeve connections on the phone jack. Solder straight pins or needles to the loose ends (from the XYL's sewing basket). Take a AAA-D flashlight battery and touch one of the pins to one end of the battery, and the other end to the other end of the battery. Did you hear a loud "click" in the headset when you touched the pins? Good. If not, figure out why.

Now comes the hard part. Find the "speaker out" wire from the radio. Poke one of the pins through this wire. Touch one of the other pins to airframe ground. Now do you have audio from the radio? Are you SURE you have the speaker out line? If you have radio audio the problem is in the audio panel OR in the interconnects between radio and audio panel.

If you don't have audio the problem is in the radio.

In either case, you know which box to take into the shop for fixit. As I understand it, there are several "online" shops that you SEND your radio to, they fix it, and send it back. I can't vouch for any of them, but I'm told they are half-price if you are willing to do the preliminary troubleshooting to find out which box it is.

Jim
 
weirdjim said:
OK, if you are going to be digging in anyway ... go to Radio Shack and get a quarter-inch phone jack.
Click to expand...

Good luck finding a Radio Shack. Let alone one with components. After the bankruptcy, Sprint was going to buy the ones they wanted to push cell phones.
 
weirdjim said:
OK, if you are going to be digging in anyway ... go to Radio Shack and get a quarter-inch phone jack. Stereo if you have to, but mono is easier. Take foot or two of 2 cheap wires and solder one end to the tip and sleeve connections on the phone jack. Solder straight pins or needles to the loose ends (from the XYL's sewing basket). Take a AAA-D flashlight battery and touch one of the pins to one end of the battery, and the other end to the other end of the battery. Did you hear a loud "click" in the headset when you touched the pins? Good. If not, figure out why.

Now comes the hard part. Find the "speaker out" wire from the radio. Poke one of the pins through this wire. Touch one of the other pins to airframe ground. Now do you have audio from the radio? Are you SURE you have the speaker out line? If you have radio audio the problem is in the audio panel OR in the interconnects between radio and audio panel.

If you don't have audio the problem is in the radio.

In either case, you know which box to take into the shop for fixit. As I understand it, there are several "online" shops that you SEND your radio to, they fix it, and send it back. I can't vouch for any of them, but I'm told they are half-price if you are willing to do the preliminary troubleshooting to find out which box it is.

Jim
Click to expand...

Sounds straightforward enough. I'll give it the ol' college try. Thank you so much for the write up Jim!
 
Yes, thanks for the write up, Jim. I definitely filed that one in the "will come in handy some day" folder.

My (much less technical input): I have had some success on older audio panels and radios, pulling them, using electrical contact cleaner on the output pins or contacts, and reinstalling them. On the troubleshooting process, I'm sure you tried deactivating squelch and turning up the volume on the MK12D when you were checking its output audio.
 
edo2000 said:
Yes, thanks for the write up, Jim. I definitely filed that one in the "will come in handy some day" folder.

My (much less technical input): I have had some success on older audio panels and radios, pulling them, using electrical contact cleaner on the output pins or contacts, and reinstalling them. On the troubleshooting process, I'm sure you tried deactivating squelch and turning up the volume on the MK12D when you were checking its output audio.
Click to expand...

Sure did. Thanks.
 
I had radio problems a few years back. I fiddled around with the old 175B a while. When I got tired of that I had an SL-30 put in by a Garmin shop. My comm is now crisp & clear.

Yeah, it cost a little $$$.
 
So I had a little time to fiddle with the radio while the plane is in for annual. I pulled the radio and cleaned the contacts up a bit with an eraser, shoved it back in, and now I have audio on speaker only. My feeble mind tells me that if I'm getting audio out to the speaker, then the radio is okay, and the problem must be somewhere down the line. Do you concur?

I'll pull the audio panel tomorrow, and see what else I can break.
 
OkieFlyer said:
So I had a little time to fiddle with the radio while the plane is in for annual. I pulled the radio and cleaned the contacts up a bit with an eraser, shoved it back in, and now I have audio on speaker only. My feeble mind tells me that if I'm getting audio out to the speaker, then the radio is okay, and the problem must be somewhere down the line. Do you concur?

I'll pull the audio panel tomorrow, and see what else I can break.
Click to expand...

The only problem with the eraser trick is that if the contacts are gold plated (flashed, actually) the eraser removes some or all of the plating. My Radio Shack still sells small spray cans of contact cleaner which (a) removes the same crud as the eraser and (b) leaves a film of cleaner on the contacts to keep them going a little longer between cleanings. If they are REALLY crudded up, spray the cleaner on a cotton rag and wipe the contacts THEN spray them to leave the aforementioned film.

The label says that the contents are tetrafluoroethane, cyclomethacone, and mineral oil (in that order). I have absolutely no idea how to synthesize this chemistry. Back in the day we used to use carbon tetrachloride, which explains a lot of how I got this way. Anybody got a formula for contact cleaner and preservative?

JIm
 
weirdjim said:
The only problem with the eraser trick is that if the contacts are gold plated (flashed, actually) the eraser removes some or all of the plating. My Radio Shack still sells small spray cans of contact cleaner which (a) removes the same crud as the eraser and (b) leaves a film of cleaner on the contacts to keep them going a little longer between cleanings. If they are REALLY crudded up, spray the cleaner on a cotton rag and wipe the contacts THEN spray them to leave the aforementioned film.

The label says that the contents are tetrafluoroethane, cyclomethacone, and mineral oil (in that order). I have absolutely no idea how to synthesize this chemistry. Back in the day we used to use carbon tetrachloride, which explains a lot of how I got this way. Anybody got a formula for contact cleaner and preservative?

JIm
Click to expand...

Thanks, Jim. Truth be told, the contacts look pretty darn clean to me, on both the radio and audio panel. I pulled the audio panel this morning and cleaned the contacts a little, again with the eraser, but I don't get after it hard enough to remove any plating, as far as I can tell. It didn't help anything. Still have audio to the speaker only. I snooped around the shop a bit, and noticed another plane with the same audio panel. I'm going to see if the fellow would be kind enough to let me test with his box. Here's what I'm thinking: If installing his box fixes the issue, then the problem has to be in my box (perhaps the Comm 1 switch). If the problem persists with his box installed, then the problem must be down the line, suggesting wiring from audio panel to intercom, or perhaps a contact on the intercom or wiring harness plug. Concur?


Didn't have much time to devote to this particular problem, between having to drill out a broken exhaust stud, and needing to go rest up for the night shift tonight. I'll hit it again soon.
 
OkieFlyer said:
Thanks, Jim. Truth be told, the contacts look pretty darn clean to me, on both the radio and audio panel. I pulled the audio panel this morning and cleaned the contacts a little, again with the eraser, but I don't get after it hard enough to remove any plating, as far as I can tell. It didn't help anything. Still have audio to the speaker only. I snooped around the shop a bit, and noticed another plane with the same audio panel. I'm going to see if the fellow would be kind enough to let me test with his box. Here's what I'm thinking: If installing his box fixes the issue, then the problem has to be in my box (perhaps the Comm 1 switch). If the problem persists with his box installed, then the problem must be down the line, suggesting wiring from audio panel to intercom, or perhaps a contact on the intercom or wiring harness plug. Concur?.
Click to expand...

What other electronics (if any) other than the #1 COM do you have wired through the audio panel? Marker beacon? #2 com? ANY other audio source?

Jim
 
weirdjim said:
What other electronics (if any) other than the #1 COM do you have wired through the audio panel? Marker beacon? #2 com? ANY other audio source? Jim
Click to expand...

Well, there's the marker beacon, although I've never even used it, and frankly, I'm not totally sure how it should work (don't judge me:(). Would I have to go fly an ILS approach to get sound over the marker beacons??? No Comm #2. I was actually thinking that if the test using the other guy's audio panel tells me that the problem lies in my audio panel, then I could rig my radio to Comm #2 and see if that works. Not sure how much work would go into that, but I would assume it's pretty straightforward.


Graueradler said:
Doesn't the speaker go through the audio panel?
Click to expand...

Yes it does. However, I believe the output to the intercom and output to speaker are separate, so that wouldn't really tell me much, I don't think. Thanks, Graueradler.

Audio panel wiring diagram:
http://trackeraff.com/IAS/manuals/Narco/CP 136/CP136-Pinout.pdf
 
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I'd suggest you pull the audio panel, inspect for bent or broken pins, then reseat it, making sure the connector is fully seated and snugged up. The locking pawl on those wind up in the wrong position and never fully engage correctly if the installer isn't paying attention. Then, eventually they start having problems like you describe.
 
I had a similar problem a couple weeks ago. While crossing the ADIZ into the bahamas, the 430 went whacko and I had constant static, It was a little better on the kx170, but that radio doesn't seem to "reach out" as far...week goes by of island hopping and getting by with poor reception, made it across the border, halfway back to Michigan, the usb cigerette adapter gets pulled out of the socket and all the static goes away...I blame it on the bermuda triangle. A new adapter and all is well. It was a "good"($20) one too. Still made in china, but I thought spending more might get me better quality.
 
Graueradler said:
That the "some where down the line" has to be in the audio panel or downstream of it. The radio and output into the audio panel is OK.
Click to expand...

How do we know that the com audio into the audio panel is OK? Some audio panels use the speaker audio to feed the speaker amp and the phones audio to feed the phones amp. Unless you have the maintenance manual for the Narco CP-136 you can't assume that one com audio input feeds both speaker and phones output.

What do you mean by the "radio and output"?

JIm
 
On the CP 135/136 pinout, I only see one input from each com radio and an output for each the speaker and the phones. The 120 does have a separate speaker output and a headphone output but it would be unusual for some one to install a com panel and leave the speaker hard wired to the receiver instead of wiring it to the CP. Of course I could be wrong but if the speaker is responding, it would seem that the radio com receiver is working and providing audio to pin J or H from Com 1 or 2 respectively and that the com panel is being successful in routing that signal to the speaker but not to the headphones. Wouldn't that indicate a problem either at the headphone/speaker selector switch or in the path between the switch and the headphones (i.e. downstream)?
 
Graueradler said:
On the CP 135/136 pinout, I only see one input from each com radio and an output for each the speaker and the phones. The 120 does have a separate speaker output and a headphone output but it would be unusual for some one to install a com panel and leave the speaker hard wired to the receiver instead of wiring it to the CP. Of course I could be wrong but if the speaker is responding, it would seem that the radio com receiver is working and providing audio to pin J or H from Com 1 or 2 respectively and that the com panel is being successful in routing that signal to the speaker but not to the headphones. Wouldn't that indicate a problem either at the headphone/speaker selector switch or in the path between the switch and the headphones (i.e. downstream)?
Click to expand...

Several of us that included a "bypass" switch on our panel designs did incorporate the speaker output of the radio to the intercom for a couple of reasons. The primary reason is that the bypass switch hardwired the #1 com directly to the aircraft headphone, speaker, and microphone jacks to take care of failure modes such as this one that we are discussing. The secondary reason was in antiquity when we had radios that glowed in the dark if you didn't load the speaker output you ran the risk of an unloaded output transformer taking a spike from the mismatch and burning a hole in the transformer insulation.

I have no idea if the 136 has this feature, but if you are telling me that the pinout has only ONE com audio input to the panel, then yes indeed, I'll argue that it has GOT to be in the panel ... we know the phones circuit is fine or the intercom wouldn't work. We know the com audio is getting to the panel or the speaker doesn't work. That leaves the box in the middle as the overwhelming choice for investigation.

JIm

JIm
 
weirdjim said:
Several of us that included a "bypass" switch on our panel designs did incorporate the speaker output of the radio to the intercom for a couple of reasons. The primary reason is that the bypass switch hardwired the #1 com directly to the aircraft headphone, speaker, and microphone jacks to take care of failure modes such as this one that we are discussing. The secondary reason was in antiquity when we had radios that glowed in the dark if you didn't load the speaker output you ran the risk of an unloaded output transformer taking a spike from the mismatch and burning a hole in the transformer insulation.

I have no idea if the 136 has this feature, but if you are telling me that the pinout has only ONE com audio input to the panel, then yes indeed, I'll argue that it has GOT to be in the panel ... we know the phones circuit is fine or the intercom wouldn't work. We know the com audio is getting to the panel or the speaker doesn't work. That leaves the box in the middle as the overwhelming choice for investigation.

JIm

JIm
Click to expand...

Jim, I'm not sure if you saw the pinout for the audio panel, but there is a link provided a few posts back. As Graueradler was saying, it appears that there is a single audio in from each radio (just com 1 in my case), then the audio panel splits it to speaker, phones, etc. Have a look, if you haven't already.
 
A kind fellow with the same audio panel was kind enough to let me borrow it to test it out in my plane. With his audio panel installed in my plane, everything worked flawlessly. So I have a bum audio panel. I'll see if there is anyone who can work on it, and if not, I guess I'll get a replacement.
 
Phones out shows as pin 13 on P101. You might open the case up and trace it back to see if you can see anything obvious.

You can find the diagram on the internet. Just google Narco CP136 installation.
 
Graueradler said:
Phones out shows as pin 13 on P101. You might open the case up and trace it back to see if you can see anything obvious.

You can find the diagram on the internet. Just google Narco CP136 installation.
Click to expand...

Hmm. But the problem has to be in the guts of the audio panel, which is a circuit board. I don't have the knowhow to do anything with that. That said, I did look over the circuit board with untrained eyes. Nothing jumped out at me.
 
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