I'm Going In... Radio Saga Continued...

Todd ...

Everybody here is trying to tell you the same thing in different words. You
have a "I'll just pull wire and everything will be all right" fetish. Get
over it. "Bad wires" have about as much chance for failure as "bad bolts".

My advice is to tune in a constant signal ... like an atis or awos and start
moving things around briskly. When the signal fails or comes back after
failure repeat the jiggle. Narrow down the jiggle area.

Jim



I'm considering opening all of the intercom jacks (two in front and two
in back) and visually inspecting the connectors and wires there too,
just for grins. I'll pull new wire for them, if I have to as well...


That's good to know... The RG-58 is much cheaper!

Everybody here is trying to tell you the same thing in different words. You
have a "I'll just pull wire and everything will be all right" fetish. Get
over it. "Bad wires" have about as much chance for failure as "bad bolts".

Okay, so I hear you... but I think where my fetish lies is not with
pulling new wires, but in making sure there is proper seating, in
anything and everything I can get to. If what I'm hearing is that Coax
and wires will have nothing to do with it, I will move on from that
thought. I was thinking corrosion, rust, ??? on a coax connector, or
connector anywhere (especially connector tray - radio), for that
matter. Even you agreed that replacing the coax "may work" and that I
would only be out a couple of bucks, worst case. Your description of
cutting the coax at a 45 degree angle led me to think that you might be
questioning the coax "connector" to radio or antenna or at least be
keeping it on a list of suspects.

My advice is to tune in a constant signal ... like an atis or awos and start
moving things around briskly. When the signal fails or comes back after
failure repeat the jiggle. Narrow down the jiggle area.

I've been using the ATIS at SAC as my constant signal, and have been
forcefully pressing the radio in and shaking it from side to side to
see if I can get it to come in, so much so that the LED's dim on the
radio as I'm pushing it in. That's never got reception to come back.
As far as other things, which I assume you are talking about wires
behind the panel, I can certainly give that a try, once I can figure
out how to do that without putting my self into an unintentional
unusual attitude. I'm 6'2" and about 2 bucks, so I can barely get
behind the panel when the plane is parked safely on the ground, let
alone 5000 feet and 100 kts.

I REALLY do appreciate all of the input, and am not TRYING to be a
knuckle-head about all of this! I'm just trying to interplote the
input I am receiving and do things that are within my capabilities.
And in this case, my capabilities don't seem to cover a very broad
spectrum!

Thanks,
Todd

three-eight-hotel wrote:
: Okay, so I hear you... but I think where my fetish lies is not with
: pulling new wires, but in making sure there is proper seating, in
: anything and everything I can get to. If what I'm hearing is that Coax
: and wires will have nothing to do with it, I will move on from that
: thought. I was thinking corrosion, rust, ??? on a coax connector, or
: connector anywhere (especially connector tray - radio), for that
: matter. Even you agreed that replacing the coax "may work" and that I
: would only be out a couple of bucks, worst case. Your description of
: cutting the coax at a 45 degree angle led me to think that you might be
: questioning the coax "connector" to radio or antenna or at least be
: keeping it on a list of suspects.

Coax isn't all that hard to replace, necessarily... BUT it can be a big pain
to route. It goes all the way to the antenna... likely a fairly long way. Soldering
the ends on (well) requires a pretty good knowledge of a soldering iron... not just
"which end to grab." Given that it's very unlikely to be that particular one, I'd
start with something else.

: My advice is to tune in a constant signal ... like an atis or awos and start
: moving things around briskly. When the signal fails or comes back after
: failure repeat the jiggle. Narrow down the jiggle area.

: I've been using the ATIS at SAC as my constant signal, and have been
: forcefully pressing the radio in and shaking it from side to side to
: see if I can get it to come in, so much so that the LED's dim on the
: radio as I'm pushing it in. That's never got reception to come back.
: As far as other things, which I assume you are talking about wires
: behind the panel, I can certainly give that a try, once I can figure
: out how to do that without putting my self into an unintentional
: unusual attitude. I'm 6'2" and about 2 bucks, so I can barely get
: behind the panel when the plane is parked safely on the ground, let
: alone 5000 feet and 100 kts.

The problem my mechanic's transponder had couldn't be induced by forcing the
radio around in the tray. It was a mechanical stop near the connector. Couldn't
really make it come and go. Of course it was further complicated by the fact that the
only way to check it was to test-fly it and ask local ATC if they could read ModeC (I
don't have a transponder interroagtor). For your COM, it should be easier.

Just as a thought... have you tried pulling out the squelch when you're unable
to receive? If you don't hear static when you can't receive, it's likely in the
wiring/connector from the radio/intercom/audiopanel/jacks. If you hear static but you
still cannot receive, then it's much more likely the radio.

: I REALLY do appreciate all of the input, and am not TRYING to be a
: knuckle-head about all of this! I'm just trying to interplote the
: input I am receiving and do things that are within my capabilities.
: And in this case, my capabilities don't seem to cover a very broad
: spectrum!

The biggest thing would be to try and make it happen on the ground so that you
can troubleshoot it. I'm not familiar with Narco's trays, but on the King ones, the
connector can be disconnected from the tray. Then you could play with that without
being stuck with the geometry of the tray. Basically, stop at the top and work
down...

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

I was thinking corrosion, rust, ???

Rust is iron oxide and will only form on iron or steel. Corrosion is a
different matter, but you can rub or spray corrosion off. The only way coax
deteriorates is in sunlight or with water inside the shield. Age is a
second order factor.




on a coax connector, or
connector anywhere (especially connector tray - radio), for that
matter. Even you agreed that replacing the coax "may work" and that I
would only be out a couple of bucks, worst case.

Yeah, as well as throwing salt over my left shoulder has kept me from being
trampled by hippopotami all my life, but I don't think replacing the salt
shaker is going to have any effect.



Your description of
cutting the coax at a 45 degree angle led me to think that you might be
questioning the coax "connector" to radio or antenna or at least be
keeping it on a list of suspects.

No, I was telling you to do that so the square-cut coax wouldn't hang up on
the grommets as you pulled it.





My advice is to tune in a constant signal ... like an atis or awos and
start
moving things around briskly. When the signal fails or comes back after
failure repeat the jiggle. Narrow down the jiggle area.

I've been using the ATIS at SAC as my constant signal, and have been
forcefully pressing the radio in and shaking it from side to side to
see if I can get it to come in, so much so that the LED's dim on the
radio as I'm pushing it in.

Do you intend to destroy your radio in the fixit process?



That's never got reception to come back.
As far as other things, which I assume you are talking about wires
behind the panel, I can certainly give that a try, once I can figure
out how to do that without putting my self into an unintentional
unusual attitude. I'm 6'2" and about 2 bucks, so I can barely get
behind the panel when the plane is parked safely on the ground, let
alone 5000 feet and 100 kts.

You CANNOT do troubleshooting at 5K and speed. You HAVE to do it on the
ground. THe easy way is to pull the front seats out and lay on the floor.
I'm 6-3 and two and a quarter, and this is the only way I can troubleshoot
any airplane except a heavy with a radio rack in the belly.




I REALLY do appreciate all of the input, and am not TRYING to be a
knuckle-head about all of this! I'm just trying to interplote the
input I am receiving and do things that are within my capabilities.
And in this case, my capabilities don't seem to cover a very broad
spectrum!

You need to get the airplane to a place where you can get at the radio with
a constant signal. You also need access to tools and such when you DO find
the problem. I think I've got an old com test set around here somewhere
that radiates a constant low level signal on 122.8, powered by a 9 volt
battery. If you'd like to come up to Grass Valley and borrow it, I'd be
glad to loan it to you ... if I can find it.

Jim

Just a (dumb?) question to the OP: Does the radio tray have a BNC connector
for the coax cable connection? Can you try a piece of short coax connected
to a 'portable' antenna attached to some type of ground plane? If this setup
works, then you'll know it's somewhere in the original coax connections, if
the radio still doesn't receive, then it would be a different connection
problem.

Are you sure the radio itself is good?

If you have already tried this, disregard...

: The weird symptom that goes along with the not receiving is the
loss of
: sidetone, when I attempt to xmit.

I'm gettting a bit lost in facts and symptoms here. Anyway, we
must bypass intercom to isolate to which box. If the Narco, it
does not know receive audio from sidetone in the circuit area of
interest, if both those signals are absent.

There's audio leveling circuitry in there to which both mic audio
and receive audio are fed. The nature of that circuit is such that
component drift through heat upsets a delicate balance, and there's
many analog swith ICs in there to turn things on and off. The fact
that you can xmit w/o hearing mic audio I believe may isolate the
fault to a certain area of that circuit.

If true that it works for a while and then stops, that's gotta be
thermal. A wire or coax connection can theoretically behave like
that, but airplanes vibrate. The thermal expansion of metal is
like what in comparison? The only wire connection for your
symptoms should be phone audio out from the comm.

The reason I'm leaning in this direction is that there are simpler
circuits in comm boxes where all your symptoms could not happen.
In the Narco design it can; it's an electronic Rube Goldberg
machine. And the only company on earth who still write code for
the MK3870 CPU chip.

Fred F.

UPDATE:

Last night, I went up to the airport and pulled out the radio, and
pulled the connector tray as far out/forward as I could. I performed a
close visual inspection and noticed something that I hadn't noticed
before... The radio and connector union seems to be made through two
24 pin connectors and two BNC connectors. The BNC connectors are an
opposing male and female (one each on the tray, and one each opposing
on the radio). What I noticed (forgive any improper terminology) is,
that the male connector on the tray seemed to be missing one tooth (for
lack of a better word) on the outer ring of the connector and the
radio, seemed to be lacking two teeth, on the outer ring of it's male
BNC connector (that's almost half!)

Aside from not being a good thing, is this a likely suspect for some of
the symptoms I have been experiencing? Replacing those two male BNC
connectors would seem like good common sense, but is this just an
unfortunate coincidence of something else being found while
troubleshooting another problem?

Look... I'm admittedly a couple of bricks short of a fireplace, when
it comes to talking circuitry and componentry, so no piling on! ;-)
I've been paying attention to all of the posts, but alot of it seems to
be going over my head. It's not like I'm not listening... I promise,
I'm not going to go pulling any wire!

I may, however, take you up, Jim, on a trip to Grass Valley to borrow
your constant signal device or bird watt meter you mentioned in a
previous post. One step at a time, though, I guess...

Thanks,
Todd

"three-eight-hotel" wrote:
... the male connector on the tray seemed to be missing one
tooth (for lack of a better word) on the outer ring of the
connector and the radio, seemed to be lacking two teeth, on
the outer ring of it's male BNC connector (that's almost half!)

Aside from not being a good thing, is this a likely suspect for
some of the symptoms I have been experiencing?
....

Whatever's goin' on there will not cause a loss of sidetone.

Fred F.

Yeah... that makes sense. Thanks!

I pulled everything from the stack this weekend and visually inspected
everything I could see... As mentioned in a previous response, every
single screw, holding in every tray, had a nut on the back of it, and
half of them became part of the permanent W/B! I took an air
compressor with me, along with the component/connector cleaner and
cleaned every connection I could. I'm going to hold off on putting the
trays back in and borrow the tools from my mechanic to do it right,
rather than figure out how I'm going to hold nuts on the back of trays
for each screw.

While I was working on this, I ran into someone up at the Ghost-town
(err, I mean Georgetown) airport that I haven't seen in a while. He
offered to let me swap out and try his audio panel, to see if that
might be the culprit! As soon as I get the trays back in place and can
reseat all of the avionics devices, I'll give it a quick check flight
to see if I can get it to fail again, then try the replacement audio
panel.

Thanks for all of the responses, and I'll provide an update when I can.

Best Regards,
Todd

I will state again, I had very similar problems with my MK12D and it
went back to the factory. It is fixed and working fine. The side tone is
a product of the radio not the audio panel. How I isolated it was
swapping the two MK12Ds I had and the problem followed the radio.
Therefore not in the trays, coax, audio panel, etc.


-------------
Regards, Ross
C-172F 180HP
KSWI


three-eight-hotel wrote:
I've read your symptoms per your orig post, and you have one odd
collection of seemingly mutually-exclusive symptoms. If you can
xmit, but not receive, it's not the coax.


The weird symptom that goes along with the not receiving is the loss of
sidetone, when I attempt to xmit. That's the part that confuses me,
and leads me to question whether I can receive or not... Maybe I am
receiving, but just can't hear it??? I don't completely understand how
the radio, intercom and audio panel all tie together, so I'm confused
at the various symptoms I am encountering. i.e. a) clear side-tone
when talking over the intercom (no depression of the PTT) and able to
talk and listen to passengers. b) obviously clear transmission
(pressing PTT) but no sidetone and passenger doesn't hear me either.
(I say obviously clear because ATC acknowledged my transmission, which
I was able to confirm over a hand-held) c) Not hearing radio calls
(confirmed by listening and hearing them on a hand-held).

Sidetone is a function of the intercom, is it not? Meaning, if I were
to bypass the intercom and plug directly into the aircraft jacks (which
I have tried) I would not hear sidetone, when I attempted to transmit.
Either way, I was unable to hear known ATC coms while plugged directly
into the aircraft jacks.


Scratchiness, followed
by silence, isn't likely the connector, nor coax. Is that what it
still does?


It seems the first time it fails, it tends to fade out with
scratchiness. The last time I flew, I was able to turn the radio off
for a few seconds and turn it back on, to find it working for a minute
or two. This worked a few times, but failed to work, at all, the last
two times I tried it. The real ****er is that once I get it on the
ground, it seems to work fine!


It sounds like a thermal fault in the squelch
circuitry. Narco uses a large fancy squelch circuit, squelching in
2 different ways and works on a hair trigger. Bad thermal behavior
of a component could cause grief. My Narco comm 120 does similar
and obviously a thermal, w/o the annunciating scratchiness.
Similar circuit; no time to pull and fix in such nice weather yet.


I just had the radio in for some questionable repairs at an avionics
shop that is a certified Narco dealer. They ran it up on the bench for
4 or 5 hours, and said that everything was within specifications... Is
this something a normal bench runup would be able to detect?


You can't pull the tray without dealing with the wires at the
connector. If you can do that, you can just visually inspect the
stuff for integrity.


At some point, before my last two flights, I crawled into that
wonderful position with my head between the rudder pedals and reached
my arm up behind the radio to see if I could feel anything out of the
ordinary (like I would know what ordinary felt like!). I grabbed at
the cables and wires and performed a wiggle-and-seat manuver for
everything I could blindly grab... My following two flights, each
nearly two hours, resulted in no radio failures. I was convinced the
problem was gone (okay, I was praying that the problem was gone).
However, the last two times I flew, it was back... This is when I
decided that I might have temporarily fixed something, but that
vibration had caught back up with me and undid what I fixed. My hope
was that removing and cleaning all connection points and making sure
everything is seated snugly when reinstalled, would fix my problem once
and for all. The worst case scenario is $20 of coax cable and pulling
back bloody stumps when I try to retrieve my arms from behind the
panel. If I take it to an avionics shop at this point, I will be
looking at a minimum of $300 to troubleshoot, and I have already dumped
nearly $600 for a questionable radio repair and a new antenna, while
shotgun troubleshooting.


For thermal, did you try flying w/o any box above and below the bad
one? That's how I know my 120's a thermal glitch.


I haven't tried that, but I did fly with a TKM slide-out loaner and
encountered a similar failure. I also put my radio in another plane
and the pilot reported that it did not fail during a nearly 3 hour
flight.

Above my radio is the audio panel, and below it is an ADF. The ADF is
inop, so I could remove it... Does the radio require the audio panel
to be useable in the airplane? Could I pull out the audio panel and
ADF, leave the radio in and plug my headsets into the aircraft (non
intercom) jacks and be able to xmit/receive? I'm willing to try
anything I can, to avoid throwing good money after bad! It would be
one thing if I could explain a set of symptoms to an avionics shop and
get an estimate to put this issue to bed, but I can't reproduce the
issue at will, unless a tech is willing to go flying with me! :-(


Per other post, RG-400 will cure anything, nor do much
performance-wise at VHF.


I don't completely follow this one??? RG-400 is or isn't necessary, as
opposed to RG-58?

Thanks for taking the time to respond!

Todd