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

I've posted twice before on the problems I have been having with my
Narco radio's:
http://groups.google.com/group/rec.a...1307ec4df68cc6

I've decided that I'm going to pull the radio and the connector tray
and run new coax from the radio to the antenna, after cleaning every
contact point I can find with contact/connector cleaner. I figure the
worst case scenario is that I will have spent $20 - $30 for cable,
which is far less than taking it into an avionics shop for more
troubleshooting! Been there, done that!

I've pulled the radio out several times during troubleshooting, but
never paid attention to what would be entailed in pulling the connector
tray. For those who have done this before, is it going to be blatently
obvious when I get in, what needs to be done? Is it pretty
straight-forward, or am I going to be squeezing my head between the
rudder pedals and scraping my arm and knuckles on all of those hidden
dangers, lurking behind the panel?

Any tips or recommendations on how to pull the connector tray?

My thought on running coax is to do it as if I were pulling electrical
wire... Tape a new coax end, to the old coax end at the tray, and pull
from the antenna end to feed the new coax through. This way, I
shouldn't have to pull any plastic.

Any suggestions or lessons learned will be greatly appreciated!

Thanks and Best Regards,
Todd

"three-eight-hotel" wrote in message
oups.com...
I've posted twice before on the problems I have been having with my
Narco radio's:
http://groups.google.com/group/rec.a...1307ec4df68cc6

I've decided that I'm going to pull the radio and the connector tray
and run new coax from the radio to the antenna, after cleaning every
contact point I can find with contact/connector cleaner. I figure the
worst case scenario is that I will have spent $20 - $30 for cable,
which is far less than taking it into an avionics shop for more
troubleshooting! Been there, done that!

It may work. At the very least you will have new cable.



I've pulled the radio out several times during troubleshooting, but
never paid attention to what would be entailed in pulling the connector
tray. For those who have done this before, is it going to be blatently
obvious when I get in, what needs to be done? Is it pretty
straight-forward, or am I going to be squeezing my head between the
rudder pedals and scraping my arm and knuckles on all of those hidden
dangers, lurking behind the panel?

The tray is generally held to the rack by four pan head or flathead screws.
If the installer was nice, he put rivnuts in the rack so all you have to do
is back the screws out. If he was not so nice, you wind up squeezing,
scraping, and bloodying getting a wrench into a LITTLE TINY gap in the rack
to hold the nut while you back the screw out.

DOn't even ASK about holding that nut when putting the tray back in. Come
to think of it, you won't have to worry about it because that nut will drop
right out of the wrench and become a permanent part of the weight and
balance ... not to be found until you pull negative g's and it relocates
itself between the master switch bus and ground.



Any tips or recommendations on how to pull the connector tray?

My thought on running coax is to do it as if I were pulling electrical
wire... Tape a new coax end, to the old coax end at the tray, and pull
from the antenna end to feed the new coax through. This way, I
shouldn't have to pull any plastic.

Cut the new coax with a 45 degree angle on the coax and put the point of the
cut down so that it has a fighting chance to wedge itself rather than
butting up against a grommet of some sort. I myself prefer safety wire
instead of tape ... and I pull the safety wire through with the old coax
THEN the new coax. That way you aren't trying to pull double thicknesses of
coax through a single thickness space.

Jim

It may work. At the very least you will have new cable

That's what I was thinking...

The tray is generally held to the rack by four pan head or flathead screws.
If the installer was nice, he put rivnuts in the rack so all you have to do
is back the screws out. If he was not so nice, you wind up squeezing,
scraping, and bloodying getting a wrench into a LITTLE TINY gap in the rack
to hold the nut while you back the screw out.

I'll keep my fingers crossed and hope for the best

DOn't even ASK about holding that nut when putting the tray back in. Come
to think of it, you won't have to worry about it because that nut will drop
right out of the wrench and become a permanent part of the weight and
balance ... not to be found until you pull negative g's and it relocates
itself between the master switch bus and ground.

Now that's funny!!! LOL!

Cut the new coax with a 45 degree angle on the coax and put the point of the
cut down so that it has a fighting chance to wedge itself rather than
butting up against a grommet of some sort.

Will do... Thanks for that tip!

I myself prefer safety wire
instead of tape ... and I pull the safety wire through with the old coax
THEN the new coax. That way you aren't trying to pull double thicknesses of
coax through a single thickness space.

I was thinking something similar, it just seemed easier to explain it
that way...

Thanks for the feedback! I'm going to try and get to it Saturday and
thought I would probably get all of it done, except pulling the new
coax (don't have any yet). I could order the exact length I would
need, after I pull the old one.

Is there a reg on using RG-400 coax or can it be RG-58? I didn't see
coax on your site, but saw the connectors... Is that something that
can be ordered through RST, if I provided you with a length?

Thanks again!
Todd

"three-eight-hotel" wrote:
I've decided that I'm going to pull the radio and the connector
tray and run new coax from the radio to the antenna,

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

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. May take just an inspection mirror. I'd use
my $400 flexible, illuminated, magnifying boroscope. Next colon
cancer check, I'm using that to then check that doctor!

An avionics tech can visually check your connector from the front,
knowing what looks normal. He can maybe feel for integrity of the
wire connections from the back, having fondled hundreds. That's
why it's easy for him; hard for us.

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.

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

Good luck!

Fred F.

RST Engineering wrote:

DOn't even ASK about holding that nut when putting the tray back in.

And since it's you doing the work, *you* will drill the holes out, borrow a
pop-rivet tool, and insert aviation quality rivnuts (like the original installer
should've done).

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.

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

"three-eight-hotel" wrote in message
ups.com...
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.


Hello. I have just arrived, so may be sticking my nose in, but this seems to
have narrowed it down quite a bit. If the radio was fine in another plane,
and another radio failed in yours, the radio is ok. It is your wiring in
your airplane. I agree it is not the antenna or coax. as this should affect
both tx and recieve. Jiggling yhe cables helped for a time. This is where I
would focus my time and money, I think.

Harvey

three-eight-hotel wrote:
: 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???

Sidetone is, by definition, NOT the audio you hear when you receive. That's
the "received audio." Sidetone is you getting to hear yourself when you transmit.

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.

The "sidetone" there is actually just the intercom functioning normally.

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)

So it has always transmitted properly?

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.

Sidetone can be done in the intercom, the radio, or both. All it's doing is
looping back your mic signal into your own headset when the transmit button is down.
It just depends on how far up the chain you go before it loops back. When I installed
my intercom and coms, the intercom was initially wired to produce the sidetone.
I reconfigured the setup so that each radio provided its own sidetone. That way I
could ensure that all the signals were going all the way to the radios (and back to
me).

Here's something to think about based on my experience. Before we finished
the interior, we had a couple of intercom jacks in the back seats just zip-tied up,
but with bare 0.250/0.208 jacks wired in. Every once in awhile, they would move so
that in-flight the jacks would touch something aluminum. That would cause a really
ugly static, intermittent signal on the intercom if it hit a MIC wire. Between that
and the possibility of the intercom sharing multiple mics together, see if that adds
something to your debug equation.


: 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!

"Fade out with scratchiness" sounds like it could be internal to the radio.

: 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?

Neither the thermal stresses nor the vibration are adequately simulated by
letting the thing warm on the bench for 5 hours. Do you have active cooling and is it
in good shape? i.e. a fan or ram-air blowing on it?

Just a thought... not too likely.

: 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.

I hear you. Troubleshooting intermittent problems sucks. Another possibility
is wrong spacers on one or more trays. My mechanic had troubles with his transponder
and intermittent connections on an encoder line or two. After a bunch of rewires,
checking, etc, we discovered that some small nuts/washers were installed on the wrong
side of the connector on the back of the tray. It was preventing the connector from
seating an additional 1/8" and causing intermittent failures on a few pins.

: 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.

From that right there, it sounds like you can rule out your radio. Don't
discount multiple *different* failures in the debug equation. Maybe it's your audio
panel or intercom?

: 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?
Doesn't *need* it, but it's probably wired to use it. If you've got a set of
direct-to-radio heaset plugs, those should still work with the ADF and audio panel
out. It also likely doesn't change anything whether they're in or not, though.

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

RG-400 shouldn't really be necessary at VHF frequencies. The materials are
better, and it has better high-frequency characteristics (e.g. transponder or DME).
At VHF it primarily serves to be more of a PITA to work with (much more rigid). It
also screwed with my compass once because it had a copper/tin-clad steel center
conductor.

-Cory

--

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

TaxSrv wrote:
: "three-eight-hotel" wrote:
: I've decided that I'm going to pull the radio and the connector
: tray and run new coax from the radio to the antenna,

: 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.

Oh, and I forgot on my other post that I concur it's most likely NOT the coax.
That doesn't really cause scratchiness.... you either have signal or you don't.
Scratchiness is caused by the signal to from your mics or to your headset (or from
within the audio panel, intercom, or radio, which is pretty much ruled out at this
point, too).

-Cory

--

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

Sidetone is, by definition, NOT the audio you hear when you receive. That's
the "received audio." Sidetone is you getting to hear yourself when you transmit.

The "sidetone" there is actually just the intercom functioning normally.

That all pretty much makes sense to me...

So it has always transmitted properly?

I'm pretty sure it has... I recall one of my first failures, while
shooting ILS approaches at SAC. After minutes of trying to figure out
why ATC wasn't responding to me, I grabbed my handheld to find out that
they had been hearing me all along. However, at that time, I was
hearing sidetone while xmitting, just not hearing audio back.

Here's something to think about based on my experience. Before we finished
the interior, we had a couple of intercom jacks in the back seats just zip-tied up,
but with bare 0.250/0.208 jacks wired in. Every once in awhile, they would move so
that in-flight the jacks would touch something aluminum. That would cause a really
ugly static, intermittent signal on the intercom if it hit a MIC wire. Between that
and the possibility of the intercom sharing multiple mics together, see if that adds
something to your debug equation.

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...

"Fade out with scratchiness" sounds like it could be internal to the radio.

That's a tough one, because I don't even know if I'm describing this
symptom well... It's very quick and is simply an indication that the
failure is occurring. It's not a long drawn out fade, and the
scratchiness is really more of a quick (but barely audible) static that
I hear, when the radio fails.

Neither the thermal stresses nor the vibration are adequately simulated by
letting the thing warm on the bench for 5 hours. Do you have active cooling and is it
in good shape? i.e. a fan or ram-air blowing on it?

Not that I am aware of???

I hear you. Troubleshooting intermittent problems sucks. Another possibility
is wrong spacers on one or more trays. My mechanic had troubles with his transponder
and intermittent connections on an encoder line or two. After a bunch of rewires,
checking, etc, we discovered that some small nuts/washers were installed on the wrong
side of the connector on the back of the tray. It was preventing the connector from
seating an additional 1/8" and causing intermittent failures on a few pins.

That 1/8" issue is one of the top things in my mind... I'm thinking
the whole exercise of pulling, cleaning and reinstalling may enable me
to get a proper seating, that may not be occurring now???

From that right there, it sounds like you can rule out your radio. Don't
discount multiple *different* failures in the debug equation. Maybe it's your audio
panel or intercom?

Possibly???

RG-400 shouldn't really be necessary at VHF frequencies. The materials are
better, and it has better high-frequency characteristics (e.g. transponder or DME).
At VHF it primarily serves to be more of a PITA to work with (much more rigid). It
also screwed with my compass once because it had a copper/tin-clad steel center
conductor.

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

Thanks to you, and to all for your input! I feel like Chevy Chase, in
Fletch, when I'm looking at this stuff! I'm pretty darn sure the whole
problem is in the Fetzer Valve... Now if I can just round up some
gauze and some ball-bearings, I think I might be able to get this
problem licked! ;-) Ohhh, and I'll have to clean the windows too,
because they've got "filth muck" all over them!

Todd