Mark 12D Problem???

On Tue, 5 Jul 2005 08:45:50 -0700, "RST Engineering"
wrote:

A classic connector symptom. "I took it out, put it back in and it worked
fine for half an hour, then crapped out again". You repositioned the
connector and it worked it's way back by vibration to it's normal
intermittent position.

Eliminate problems one by one. Does your audio panel have a bypass mode or
can you patch-pin around it to hardwire the radio into the aircraft system
and eliminate all the other radios? What other avionics are sharing the
audio panel wiring? Can you shut everything down except this ONE radio to
see if it really is the radio?

As to the Narco dealer replacing an intermittent diode ... hmmm ... never
yet found an "intermittent" diode in the last 50 years of designing and
fixing this stuff. The diode is good or it isn't. There isn't any
in-between. Intermittent solder connections ... thousands. Intermittent
semiconductor parts ... for all intents and purposes never.

Jim

I would tend to agree, they sould either work or die, but...!

We have 2x Narco 12D+ and one had an intermittent transmitt audio (and
sidetone) loss. We decided to leave it until the next service and use
the other set. That too became intermittent a couple of times, but not
at the same time. Just before being sent away they both decided to
fail on me at the same time.
I understand it was a known problem and due to a zener diode. Both
sets were repaired and have been working for 6 months.

It's not likely to be temperature related as it was during the winter
in Scotland.


"three-eight-hotel" wrote in message
roups.com...
I have been struggling with a radio problem for some time now and am
having a tough time finding the real "root cause"! (I have a Narco -
Mark 12D)

It started several months back, when I would occaisionally get a "stuck
mike". After several phases of trouble-shooting, it appeared to be a
problem with the audio panel, which was replaced and seemed to solve
the problem.

A month or so ago, I lost contact with ATC while shooting some practice
approaches... Apparently, they could hear me, but I couldn't hear them
(confirmed by using my hand-held). Ever since then, I have been having
strange issues with the radio, but it will occaisionally work fine for
20 minutes or so???

Symptoms:
1. No side-tone when transmitting???
2. Occaisional loss of reception on known frequencies
3. No response (on known frequencies) to transmissions

I took the radio into a Narco dealer and they confirmed a problem with
the transmission switch (replaced a diode) and yellow-tagged the radio.
I put the radio in the plane and it worked like a champ for about 30
minutes and started to exhibit the symptoms again??? I took it back to
the dealer and the bench tested it for a couple of hours and said that
it worked fine and everything was within specs! :-(

I'm worried about throwing good money after bad and don't even know
where to begin in resolving this issue. (I can't afford to throw a lot
of money at new avionics and would like to get what I have working, if
at all possible)

Does anybody have any recommendations at troubleshooting this problem?
My mechanic is at a loss as well. The loss of side-tone, while
transmitting, seems to be an interesting issue...

Any suggestions would be greatly appreciated!