Mark 12D Problem???

Well... My old instructor just took a student up in a 150, with my
Narco in it and flew it for just over an hour... It didn't act up at
all...

Next test... A (known to be working) TKM has been put in my plane and
I will go out and give it a shot this weekend. I'll post the results
on Monday...

Best Regards,
Todd

Okay, so it's not the radio..... ??? I took off with the TKM,
yesterday morning, and it failed within 20 minutes! Same symptoms!
Reception started to get scratchy, then no transmission with a loss of
side-tone...

I'm not sure if it makes sense to isolate the audio panel from the
radio, since we have confirmed that the radio works in another plane
and a working radio does not work in my plane???

Is the audio panel the logical culprit? I failed to mention earlier
that the audio panel had been replaced last year with a used one,
because I was encountering a "stuck-mike"... However, the radio worked
fine for several months as I finished up my IFR work and took my
check-ride in the plane.

I haven't spoken with my mechanic yet this morning, but I'm thinking
that he is leaning towards the audio panel as well... Any next step
suggestions? See if I can swap out the audio panel with a working one
too, I guess???

Thanks for the feedback!

Clyde - I have seen a lot of unhappy Narco owners in the newsgroups,
and probably wouldn't make it one of my top choices if I were to go
down the road of buying a new radio. At this point, I'm trying not to
throw good money after bad and am just trying to get up in the air
again without having to rely on my hand-held! ;-) If the day comes,
where I am faced with the purchase of a new radio, I will probably bite
the bullet and see how I can tweak the finances to put in something
like a Garmin GNS with built in com. As for a second radio, I'll have
to start hitting the research! Best Regards!

Think about it, grasshopper. The receive circuits ("scratchy reception")
and transmit circuits (no transmission & loss of sidetone) are completely
separated in the audio panel.

What is the ONLY element in the chain common to both transmit and receive?
Do the words antenna/feedline strike a familiar note?

Jim



"three-eight-hotel" wrote in message
oups.com...
Okay, so it's not the radio..... ??? I took off with the TKM,
yesterday morning, and it failed within 20 minutes! Same symptoms!
Reception started to get scratchy, then no transmission with a loss of
side-tone...

I'm not sure if it makes sense to isolate the audio panel from the
radio, since we have confirmed that the radio works in another plane
and a working radio does not work in my plane???

Okay, so bear with me cuz technical electronics is not my forte'. I
can talk software and web development all day long, but circuit talk
hurts my head... ;-)

If I get scratchy to loss of reception, that's going through one
circuit path in the audio panel. No transmission and side-tone loss is
taking another route in the audio panel. So what I think you are
saying is that it is not likely that both circuits went bad at the same
time?

The antenna was just replaced with a brand new one and my old one is
currently on eBay to minimize my losses! That would leave the
feedline... Is that something I could easily replace on my own? Would
that be a legal thing for me to repair or should I just point my
mechanic in that direction and eat the cost of the feedline and
installation labor?

Sorry for being such a knuckle-head... I guess I should have paid more
attention in those electonics classes? I do remember something like
"Bad Boys Rape Our Young Girls But Violet Gives Willingly"??? ;-)

Greatly appreciate the input!!!

If I get scratchy to loss of reception, that's going through one
circuit path in the audio panel. No transmission and side-tone loss is
taking another route in the audio panel. So what I think you are
saying is that it is not likely that both circuits went bad at the same
time?

That is correct. The odds of BOTH circuits failing at the same time comes
somewhere around the odds of winning an argument with an FAA inspector.

Receive audio comes in one pin, goes to an audio processor, and out to a
phones/speaker amplifier. That's one channel. Sidetone also goes through
that channel.

Microphone audio comes in one pin, mic key comes in another pin, both go
pretty much unimpeded (except for a little diode switching) back to the
transmitter.

BTW, how do you KNOW you aren't transmitting? Are you transmitting carrier
but no audio? Or no carrier at all?

Does this happen on the ground? It seems to take about a half hour for the
symptoms to appear. Does it happen with just the radios on and the engine
stopped? You need to keep the battery up to voltage while checking it
static, so get one of those little 5-10 amp battery chargers to keep the
bats batting while you do the test.



The antenna was just replaced with a brand new one and my old one is
currently on eBay to minimize my losses! That would leave the
feedline... Is that something I could easily replace on my own? Would
that be a legal thing for me to repair or should I just point my
mechanic in that direction and eat the cost of the feedline and
installation labor?

Always look at the LAST thing you did before a failure to localize the
problem. How do you KNOW the antenna is good? Can you get at the connector
at the base of the antenna to look at the possible corrosion and/or tarnish
of the silver plated body? And is the center pin pushed back into the body
of the connector? The tip of the gold plated center pin ought to be nearly
flush with the bottom plane of the connector. Me? I'd put a bidirectional
("Bird") wattmeter in the line and see what was happening when the transmit
failure mode happens.

Simply replacing the feedline is doing what is called "shotgun analysis".
That is, start replacing parts until it works right. That's lousy practice.
Besides, what makes you think a regular mechanic knows how to put an RF
connector onto coax? Most mechanics have less knowledge of electronics than
you do. Some are great. Others are machinists, engine gurus, sheetmetal
wizards, etc.. We all have our specialties.

As to the legality ... hmmm. Ron Natalie, do you know if the radio coax is
connected to the landing light circuit {;-) THe point being, what is
"easily" replaceable? Most aircraft run the coax along the instrument
panel, up the door post, across the headliner, through the aft bulkhead,
along the fuselage formers until it comes to the antenna. Other than
tearing the airplane completely apart, it is fairly simple to replace. Like
I said, go to all that work just to find that it isn't the problem? Not me.




Sorry for being such a knuckle-head... I guess I should have paid more
attention in those electonics classes? I do remember something like
"Bad Boys Rape Our Young Girls But Violet Gives Willingly"??? ;-)

"Better Be Ready Or Your Great Big Venture Goes West".


Jim

On Mon, 11 Jul 2005 10:09:30 -0700, "RST Engineering"
wrote:

. . .THe point being, what is
"easily" replaceable? Most aircraft run the coax along the instrument
panel, up the door post, across the headliner, through the aft bulkhead,
along the fuselage formers until it comes to the antenna. Other than
tearing the airplane completely apart, it is fairly simple to replace. Like
I said, go to all that work just to find that it isn't the problem? Not me.

Looking at the antenna connector is a good idea. But for shotgun
troubleshooting, I wouldn't be averse to temporarily running a length
of coax from the back of the panel through the cabin to the antenna
just to get a data point..

Don

There's an idea. If the antenna has a connector on both ends (radio as well
as antenna) I've sure got enough 50' cables that we could string one on a
temporary basis between radio and antenna just to eliminate that
possibility. While we are at it, we could patch in a Bird bidirectional
wattmeter and the fellow would at least know if he was putting juice into
the antenna. I'd be happy to lend him both, but NOT between now and
Oshkosh.

Jim




"Don Tuite" wrote in message
...
On Mon, 11 Jul 2005 10:09:30 -0700, "RST Engineering"
wrote:

. . .THe point being, what is
"easily" replaceable? Most aircraft run the coax along the instrument
panel, up the door post, across the headliner, through the aft bulkhead,
along the fuselage formers until it comes to the antenna. Other than
tearing the airplane completely apart, it is fairly simple to replace.
Like
I said, go to all that work just to find that it isn't the problem? Not
me.

Looking at the antenna connector is a good idea. But for shotgun
troubleshooting, I wouldn't be averse to temporarily running a length
of coax from the back of the panel through the cabin to the antenna
just to get a data point..

Don