Transponder issue

I have a King KT76 transponder that has picked up a little problem. It
takes about 10 minutes before it starts transmitting the mode C
information. ATC is getting the transmission alright, there is just no
altitude information.

It started doing this about a week ago and has been ever since. Once it
starts transmitting mode C, it seems to work flawlessly.

Any idea what is the problem?

Has anyone see this before?

My biggest concern is that it may stop altogether. I do a lot of
instrument flying, so that would not be good.

We have a KT76 with an ACKA-30 encoder. Your problem may not be the
transponder, but a slow warm up on the encoder.

BT

"Jimmy B." wrote in message
ink.net...
I have a King KT76 transponder that has picked up a little problem. It
takes about 10 minutes before it starts transmitting the mode C
information. ATC is getting the transmission alright, there is just no
altitude information.

It started doing this about a week ago and has been ever since. Once it
starts transmitting mode C, it seems to work flawlessly.

Any idea what is the problem?

Has anyone see this before?

My biggest concern is that it may stop altogether. I do a lot of
instrument flying, so that would not be good.

I'll second the encoder comment. The normal failure mode of KT-76's is
for the tube to take some time to come to life, and that means no mode
a or mode c as far as ATC is concerned. If they're getting the mode a,
but no altitude, that sounds like the encoder.

That's not the transponder, it's the encoder. The little oven in the
encoder starts to wear out and take longer to heat up to the right temp.



Jimmy B. wrote:
I have a King KT76 transponder that has picked up a little problem. It
takes about 10 minutes before it starts transmitting the mode C
information. ATC is getting the transmission alright, there is just no
altitude information.

It started doing this about a week ago and has been ever since. Once it
starts transmitting mode C, it seems to work flawlessly.

Any idea what is the problem?

Has anyone see this before?

My biggest concern is that it may stop altogether. I do a lot of
instrument flying, so that would not be good.

"JB" == Jimmy B writes:
JB Has anyone see this before?

Others have mentioned the encoder. When I rented planes several had
the same problem you're describing.

The encoder on my Aircoupe went out on a cross-country, I noticed it
when Seattle Approach told me. The fix was very easy, buy another
encoder and have an avionics tech install and test it.

I had the same problem with mine (KT76 with Terra encoder). As the other
posters suggested, the problem was with my encoder (Would not warm up)
"Bob Fry" wrote in message
...
"JB" == Jimmy B writes:
JB Has anyone see this before?

Others have mentioned the encoder. When I rented planes several had
the same problem you're describing.

The encoder on my Aircoupe went out on a cross-country, I noticed it
when Seattle Approach told me. The fix was very easy, buy another
encoder and have an avionics tech install and test it.

Jimmy B. wrote:
I have a King KT76 transponder that has picked up a little problem. It
takes about 10 minutes before it starts transmitting the mode C
information. ATC is getting the transmission alright, there is just no
altitude information.
snip

I agree with everyone else. It's the encoder. Had the same thing
happen a year a couple years back.

I'll add the following recommendations:

1) buy a new encoder -- don't try to repair the existing one. It rarely
makes financial sense. The ACK is the least expensive. The Sandia the
most expensive. They differ in maximum approved altitude, number / type
of outputs (serial vs. gray code), and features (the Sandia has an
altitude monitor and 10' resolution).

2) if you have any plans to upgrade to a GPS or transponder that can
utilize it, buy an encoder that provides 10' resolution. They're a bit
more expensive, but they're worth it, IMHO.

-Doug

--
--------------------
Doug Vetter, CFIMEIA

http://www.dvcfi.com
--------------------

Thanks to all who mentioned the encoder. Do any of you remember how
much it cost to have the encoder replaced?




Doug Vetter wrote:
Jimmy B. wrote:

I have a King KT76 transponder that has picked up a little problem.
It takes about 10 minutes before it starts transmitting the mode C
information. ATC is getting the transmission alright, there is just
no altitude information.

snip

I agree with everyone else. It's the encoder. Had the same thing
happen a year a couple years back.

I'll add the following recommendations:

1) buy a new encoder -- don't try to repair the existing one. It rarely
makes financial sense. The ACK is the least expensive. The Sandia the
most expensive. They differ in maximum approved altitude, number / type
of outputs (serial vs. gray code), and features (the Sandia has an
altitude monitor and 10' resolution).

2) if you have any plans to upgrade to a GPS or transponder that can
utilize it, buy an encoder that provides 10' resolution. They're a bit
more expensive, but they're worth it, IMHO.

-Doug

--
--------------------
Doug Vetter, CFIMEIA

http://www.dvcfi.com
--------------------

Four screws, one static line and a single connector. Do it yourself.

Mike
MU-2


"Jimmy B." wrote in message
ink.net...
Thanks to all who mentioned the encoder. Do any of you remember how much
it cost to have the encoder replaced?




Doug Vetter wrote:
Jimmy B. wrote:

I have a King KT76 transponder that has picked up a little problem. It
takes about 10 minutes before it starts transmitting the mode C
information. ATC is getting the transmission alright, there is just no
altitude information.

snip

I agree with everyone else. It's the encoder. Had the same thing happen
a year a couple years back.

I'll add the following recommendations:

1) buy a new encoder -- don't try to repair the existing one. It rarely
makes financial sense. The ACK is the least expensive. The Sandia the
most expensive. They differ in maximum approved altitude, number / type
of outputs (serial vs. gray code), and features (the Sandia has an
altitude monitor and 10' resolution).

2) if you have any plans to upgrade to a GPS or transponder that can
utilize it, buy an encoder that provides 10' resolution. They're a bit
more expensive, but they're worth it, IMHO.

-Doug

--
--------------------
Doug Vetter, CFIMEIA

http://www.dvcfi.com
--------------------

Jimmy B. wrote:
Thanks to all who mentioned the encoder. Do any of you remember how
much it cost to have the encoder replaced?

If you replace it with the same thing, it takes a few minutes (plus whatever
wiggle time you take to get in position to reach it). You only need the tech to
test it and sign off your work.

George Patterson
Why do men's hearts beat faster, knees get weak, throats become dry,
and they think irrationally when a woman wears leather clothing?
Because she smells like a new truck.