Mark 12D Issues (Troubleshooting Update)

I had posted an issue I was having, regarding my Narco radios, back
before Osh and got some valuable feedback:

http://groups.google.com/group/rec.a...09e45844bccf31


What I was lacking was some decent troubleshooting! This weekend, I
took my brother-in-law up in the plane and handed him a handheld, and
we tried several different things... I'd like to throw them out to see
if this narrows down the possibilities to those of you with far more
expertise in avionics/electronics than I!

1. We departed our local airport, both of us plugged into the intercom
jacks and I made a radio call (and heard others making calls on the
same frequency). I had side-tone in my transmissions and everything
seemed fine

2. 5 minutes after take-off, I noticed a constant scratchy reception
(continuous static, with something resembling radio calls through the
fuzz)... I tuned to a local ATC frequency and switched over, noticing
no difference in static.

3. I had my passenger plug into the same ATC frequency and indicate
whether or not he was hearing any transmissions between ATC and other
aircraft, as I was hearing static... He was in fact listenting to coms
between ATC and other aircraft (loud and clear)

4. 5 or so minutes after that, there was silence on my radio! I tuned
to the local frequency and tried to make a "radio-check" call, and
there was no side-tone. From my point of view, plugged into the
intercom, I had a completely dead radio (complete silence with no
side-tone on transmission)

5. I had my passenger tune to the same local frequency (on the
hand-held), and performed another "radio-check" call. The passenger
heard me loud and clear, yet I had no side-tone and still had silence
on the radio.

6. I then tuned to the local ATC frequency and had the passenger tune
to the same frequency. I unplugged my headsets from the intercom jacks
and plugged them straight into the aircraft jacks. I had the passenger
give me an indication if he was hearing coms between ATC and other
aircraft. He was hearing coms, yet I was still experiencing silence.

7. I then plugged back into the intercom jacks and made a "radio-check"
call to ATC. My passenger heard my call on the ATC frequency and also
heard ATC respond to me... "LOUD AND CLEAR"!!! ??? I still had
silence, and no side-tone on transmission.

So it appears as though I am transmitting fine (without side-tone
though), but I am receiving nothing. Sometimes everything will work
normally for 30-45 minutes before these symptoms start to appear. The
last few threads of the original post were leading me to believe that
this could be a COAX issue between the radio and the antenna... Does
this still seem like a possibility?

The radio has been run up on a bench for 4-5 hours and supposedly,
everything is within specifications. (I also threw a working radio in
my plane and was able to encounter a failure with it). The antenna is
brand new and was replaced during this troubleshooting process.

Does anybody have an idea of what the issue is? I would really like to
have it narrowed down to one or two possibilities before I go back to
the mechanic and start taking things apart. My semi-shotgun approach
has already cost me a fair amount of money and I am no better off today
than I was when we started this process.

Thanks for listening and thanks in advance for any input!

Best Regards,
Todd

On 6-Sep-2005, "three-eight-hotel" wrote:

So it appears as though I am transmitting fine (without side-tone
though), but I am receiving nothing. Sometimes everything will work
normally for 30-45 minutes before these symptoms start to appear. The
last few threads of the original post were leading me to believe that
this could be a COAX issue between the radio and the antenna... Does
this still seem like a possibility?

Unlikely. The same antenna is used for both transmit and receive, and would
have no effect on sidetone in any case.


The radio has been run up on a bench for 4-5 hours and supposedly,
everything is within specifications. (I also threw a working radio in
my plane and was able to encounter a failure with it). The antenna is
brand new and was replaced during this troubleshooting process.

Does anybody have an idea of what the issue is? I would really like to
have it narrowed down to one or two possibilities before I go back to
the mechanic and start taking things apart. My semi-shotgun approach
has already cost me a fair amount of money and I am no better off today
than I was when we started this process.

My first guess was a problem in the intercom, but since you bypassed it
without effect that eliminates that possibility.

Most likely, based upon your troubleshooting results, the audio output from
the radio is intermittent. However, since the same problem was observed
using another radio, this suggests two possibilities. One is the connector
in the radio mounting tray. The contact for audio output (which carries
both sidetone and receive audio) could be intermittent. The other
possibility (unless you have eliminated it in your troubleshooting, which is
quite likely) is that your headset is defective and that there is nothing
wrong with the radio.

First, eliminate the headset if you have not done so already. If it is OK,
I'd focus on the tray connector.

-Elliott Drucker



--
-Elliott Drucker

Thanks Elliott!

My passenger was also experiencing the same symptoms I was, while his
headsets were plugged into the intercom system. First, he heard the
same scratchiness as the radio started to fail, then silence. He also
didn't hear my transmissions, when I lost side-tone and never heard any
transmissions between ATC and other traffic while on the local ATC
frequency.

That doesn't necessarily rule out a headset problem, but may make it a
less likely probability since we both seemed to experience the same
symptoms at the same time.

The connector, however, is suspect. Jim Weir had suggested I purchase
some connector cleaner spray, which I did and applied. That just
ensured the connectors were clean, but doesn't guarantee that the
connection is good. I will call the local avionics shop and see if
they can easily check a connector issue!

Thanks a bunch!
Todd

I have a 1977 Cessna R172K. You've not said what your a/c is, but my
experience seems similar and may give you a clue.

One day I couldn't receive SJC ground when I switched to #2 radio after I
landed. When later troubleshooting the problem, I discovered a relay hanging
under the instrument panel that is activated whenever I press the
yoke-mounted transmit button. Among other things, it interrupts the receive
side to the headset - so no sidetone when plugged directly into the jacks
under the instrument panel. After unplugging/replugging/tapping the relay
(and if I recall, trying to squirt contact cleaner into it), the problem has
gone away, never to reappear (knock on wood). Note that this relay is
between the headset jacks and the Cessna audio panel. I have no idea whether
this was original or some add-on jury-rig.

Another anecdote of general interest. I've owned my a/c since 1990. Came
with one MK12D slide-in replacement, and I soon after bought another MK12D
slide-in replacement for my other Cessna radio which had died. I continued
to have intermittent problems over the next several years, usually corrected
by reseating the radio in the tray. Finally it got to be very irritating.
After concerted effort at troubleshooting, I discovered that one of my
NAV/COM trays was actually 1/8 " longer than the other! Even with the radio
fully seated, the plugs at the back were barely making contact. I found a
used tray at a local avionics shop that was the same length as the shorter
one. With that in place, I've had no problem with it since (again, knock on
wood).

Deane Judd
N1514V

"three-eight-hotel" wrote in message
oups.com...
I had posted an issue I was having, regarding my Narco radios, back
before Osh and got some valuable feedback:


http://groups.google.com/group/rec.a...09e45844bccf31


What I was lacking was some decent troubleshooting! This weekend, I
took my brother-in-law up in the plane and handed him a handheld, and
we tried several different things... I'd like to throw them out to see
if this narrows down the possibilities to those of you with far more
expertise in avionics/electronics than I!

1. We departed our local airport, both of us plugged into the intercom
jacks and I made a radio call (and heard others making calls on the
same frequency). I had side-tone in my transmissions and everything
seemed fine

2. 5 minutes after take-off, I noticed a constant scratchy reception
(continuous static, with something resembling radio calls through the
fuzz)... I tuned to a local ATC frequency and switched over, noticing
no difference in static.

3. I had my passenger plug into the same ATC frequency and indicate
whether or not he was hearing any transmissions between ATC and other
aircraft, as I was hearing static... He was in fact listenting to coms
between ATC and other aircraft (loud and clear)

4. 5 or so minutes after that, there was silence on my radio! I tuned
to the local frequency and tried to make a "radio-check" call, and
there was no side-tone. From my point of view, plugged into the
intercom, I had a completely dead radio (complete silence with no
side-tone on transmission)

5. I had my passenger tune to the same local frequency (on the
hand-held), and performed another "radio-check" call. The passenger
heard me loud and clear, yet I had no side-tone and still had silence
on the radio.

6. I then tuned to the local ATC frequency and had the passenger tune
to the same frequency. I unplugged my headsets from the intercom jacks
and plugged them straight into the aircraft jacks. I had the passenger
give me an indication if he was hearing coms between ATC and other
aircraft. He was hearing coms, yet I was still experiencing silence.

7. I then plugged back into the intercom jacks and made a "radio-check"
call to ATC. My passenger heard my call on the ATC frequency and also
heard ATC respond to me... "LOUD AND CLEAR"!!! ??? I still had
silence, and no side-tone on transmission.

So it appears as though I am transmitting fine (without side-tone
though), but I am receiving nothing. Sometimes everything will work
normally for 30-45 minutes before these symptoms start to appear. The
last few threads of the original post were leading me to believe that
this could be a COAX issue between the radio and the antenna... Does
this still seem like a possibility?

The radio has been run up on a bench for 4-5 hours and supposedly,
everything is within specifications. (I also threw a working radio in
my plane and was able to encounter a failure with it). The antenna is
brand new and was replaced during this troubleshooting process.

Does anybody have an idea of what the issue is? I would really like to
have it narrowed down to one or two possibilities before I go back to
the mechanic and start taking things apart. My semi-shotgun approach
has already cost me a fair amount of money and I am no better off today
than I was when we started this process.

Thanks for listening and thanks in advance for any input!

Best Regards,
Todd

I recently went though two issues with a MK12D and were resolved by
Narco. The first one was that I would also loose sidetone and not be
transmitting. We could never find the problem in the avionics shop on
the bench. It would not happen all the time. To comfirm that this
problem was in the radio and not elsewhere in the system, I swapped the
two MK12Ds in the radio stack and the problem followed the radio. It was
a specific radio problem. I sent the radio to Narco with my
troubleshooting and they found several issues with the old radio, one of
which could cause the problems I was having. I got the radio back and no
further "no sidetone" problems. However, I started having another
problem with the receive audio, where it would just drop out. I got in
the habit of pulling the volume knob out to be sure I still had audio.
And several times I would not. I contacted Narco and sent it back under
the repair wannenty. This just happened to be a defective volume
control. I got the radio back and now I have not had any problems in the
20 hours I have on it. Narco did a good job. Now to send in the other
radio for some needed R&R: bad display and frequecy not always indexing
when turning the knob.

Regards, Ross
C-172F 180HP
KSWI


three-eight-hotel wrote:
I had posted an issue I was having, regarding my Narco radios, back
before Osh and got some valuable feedback:

http://groups.google.com/group/rec.a...09e45844bccf31


What I was lacking was some decent troubleshooting! This weekend, I
took my brother-in-law up in the plane and handed him a handheld, and
we tried several different things... I'd like to throw them out to see
if this narrows down the possibilities to those of you with far more
expertise in avionics/electronics than I!

1. We departed our local airport, both of us plugged into the intercom
jacks and I made a radio call (and heard others making calls on the
same frequency). I had side-tone in my transmissions and everything
seemed fine

2. 5 minutes after take-off, I noticed a constant scratchy reception
(continuous static, with something resembling radio calls through the
fuzz)... I tuned to a local ATC frequency and switched over, noticing
no difference in static.

3. I had my passenger plug into the same ATC frequency and indicate
whether or not he was hearing any transmissions between ATC and other
aircraft, as I was hearing static... He was in fact listenting to coms
between ATC and other aircraft (loud and clear)

4. 5 or so minutes after that, there was silence on my radio! I tuned
to the local frequency and tried to make a "radio-check" call, and
there was no side-tone. From my point of view, plugged into the
intercom, I had a completely dead radio (complete silence with no
side-tone on transmission)

5. I had my passenger tune to the same local frequency (on the
hand-held), and performed another "radio-check" call. The passenger
heard me loud and clear, yet I had no side-tone and still had silence
on the radio.

6. I then tuned to the local ATC frequency and had the passenger tune
to the same frequency. I unplugged my headsets from the intercom jacks
and plugged them straight into the aircraft jacks. I had the passenger
give me an indication if he was hearing coms between ATC and other
aircraft. He was hearing coms, yet I was still experiencing silence.

7. I then plugged back into the intercom jacks and made a "radio-check"
call to ATC. My passenger heard my call on the ATC frequency and also
heard ATC respond to me... "LOUD AND CLEAR"!!! ??? I still had
silence, and no side-tone on transmission.

So it appears as though I am transmitting fine (without side-tone
though), but I am receiving nothing. Sometimes everything will work
normally for 30-45 minutes before these symptoms start to appear. The
last few threads of the original post were leading me to believe that
this could be a COAX issue between the radio and the antenna... Does
this still seem like a possibility?

The radio has been run up on a bench for 4-5 hours and supposedly,
everything is within specifications. (I also threw a working radio in
my plane and was able to encounter a failure with it). The antenna is
brand new and was replaced during this troubleshooting process.

Does anybody have an idea of what the issue is? I would really like to
have it narrowed down to one or two possibilities before I go back to
the mechanic and start taking things apart. My semi-shotgun approach
has already cost me a fair amount of money and I am no better off today
than I was when we started this process.

Thanks for listening and thanks in advance for any input!

Best Regards,
Todd

I have a 1977 Cessna R172K. You've not said what your a/c is, but my experience seems similar and may give you a clue

My plane is a 1976 Cessna 172M (Skyhawk), and the Narco is a slide out
replacement for the Cessna radios.

I discovered a relay hanging under the instrument panel that is activated whenever I press the yoke-mounted transmit button. Among other things, it interrupts the receive side to the headset - so no sidetone when plugged directly into the jacks under the instrument panel

I have PTT on both yokes with intercomm jacks on both sides. The
problem seems to exist in both sides, although that doesn't mean they
both don't run to a common relay??? I can certainly look... ;-)

After concerted effort at troubleshooting, I discovered that one of my NAV/COM trays was actually 1/8 " longer than the other! Even with the radio fully seated, the plugs at the back were barely making contact. I found a used tray at a local avionics
shop that was the same length as the shorter one

This is seeming more and more like a likely possibility. I'm
considering taking the plane back to the avionics shop and seeing if
they can troubleshoot an issue between the tray connector and the
radio.

Thanks much for the response!
Todd

I recently went though two issues with a MK12D and were resolved by Narco. The first one was that I would also loose
sidetone and not be transmitting

We could never find the problem in the avionics shop on the bench

Wow! This would be a huge bummer, having already spent ~$400 to
replace a transmission switch diode??? I was, however, able to
duplicate the problem with a "known to be working" TKM radio, and an
old "original" Cessna radio.

However, I started having another problem with the receive audio, where it would just drop out. I got in the habit of pulling the volume knob out to be sure I still had audio. And several times I would not.

So many things to try and so many different scenarios for utilizing my
passenger with the handheld, that I don't recall playing with the
volume control (pulling it out)... Shoot!!! I'll have to try that one
next time I go up!

Thanks a lot for your response. The feedback from these groups is very
helpful and gives me things to try that I may not think of or forget
during this frustrating process!

Best Regards,
Todd

What kind of intercom are you using. We had quite a time getting our
Flightcom intercom to interface with our Narco's. Sidetone was a major
hassle.

Al
1964 Skyhawk
KSFF-Spokane, WA

three-eight-hotel wrote:
I had posted an issue I was having, regarding my Narco radios, back
before Osh and got some valuable feedback:

http://groups.google.com/group/rec.a...09e45844bccf31


What I was lacking was some decent troubleshooting! This weekend, I
took my brother-in-law up in the plane and handed him a handheld, and
we tried several different things... I'd like to throw them out to see
if this narrows down the possibilities to those of you with far more
expertise in avionics/electronics than I!

1. We departed our local airport, both of us plugged into the intercom
jacks and I made a radio call (and heard others making calls on the
same frequency). I had side-tone in my transmissions and everything
seemed fine

2. 5 minutes after take-off, I noticed a constant scratchy reception
(continuous static, with something resembling radio calls through the
fuzz)... I tuned to a local ATC frequency and switched over, noticing
no difference in static.

3. I had my passenger plug into the same ATC frequency and indicate
whether or not he was hearing any transmissions between ATC and other
aircraft, as I was hearing static... He was in fact listenting to coms
between ATC and other aircraft (loud and clear)

4. 5 or so minutes after that, there was silence on my radio! I tuned
to the local frequency and tried to make a "radio-check" call, and
there was no side-tone. From my point of view, plugged into the
intercom, I had a completely dead radio (complete silence with no
side-tone on transmission)

5. I had my passenger tune to the same local frequency (on the
hand-held), and performed another "radio-check" call. The passenger
heard me loud and clear, yet I had no side-tone and still had silence
on the radio.

6. I then tuned to the local ATC frequency and had the passenger tune
to the same frequency. I unplugged my headsets from the intercom jacks
and plugged them straight into the aircraft jacks. I had the passenger
give me an indication if he was hearing coms between ATC and other
aircraft. He was hearing coms, yet I was still experiencing silence.

7. I then plugged back into the intercom jacks and made a "radio-check"
call to ATC. My passenger heard my call on the ATC frequency and also
heard ATC respond to me... "LOUD AND CLEAR"!!! ??? I still had
silence, and no side-tone on transmission.

So it appears as though I am transmitting fine (without side-tone
though), but I am receiving nothing. Sometimes everything will work
normally for 30-45 minutes before these symptoms start to appear. The
last few threads of the original post were leading me to believe that
this could be a COAX issue between the radio and the antenna... Does
this still seem like a possibility?

The radio has been run up on a bench for 4-5 hours and supposedly,
everything is within specifications. (I also threw a working radio in
my plane and was able to encounter a failure with it). The antenna is
brand new and was replaced during this troubleshooting process.

Does anybody have an idea of what the issue is? I would really like to
have it narrowed down to one or two possibilities before I go back to
the mechanic and start taking things apart. My semi-shotgun approach
has already cost me a fair amount of money and I am no better off today
than I was when we started this process.

Thanks for listening and thanks in advance for any input!

Best Regards,
Todd

I'm not sure??? It's a fairly generic looking intercom, and doesn't
have a model name or number on it???

I've owned the plane for 3 years now, and flew it with no radio
problems for the first 2 years. This problem just crept up 6, or so,
months back.

In the occurences where I'm able to fly for 45+ minutes, before the
radio fails, it works very well. I send and receive loud and clear,
and would have no indication of any problems whatsoever. That is what
has me leaning towards a connection issue (although I'm not sure if
heat is ruled out as an issue either???).

Thanks for the response! I'll take all the input I can get, because I
am at my wits-end and just want this nightmare to be over! The more
information I can take to the avionics shop, or to my mechanic, the
better!

Best Regards,
Todd

I guess I should have mentioned that it is a "panel-mounted" 4-place
intercom... It has jacks mounted to the aircraft, positioned at all
four seats. I recall using a portable Flightcom intercom at one point
and wanted to make the distinction.

Thanks!
Todd