J

jeffsvan

Well Known Member
I have a Narco AR850 15 pin encoder wired to a KT76 transponder tray (It has a AT165 replacement transponder installed).
This has been functioning nicely for the last 2 years.
I am now installing a 430W and need to tap into the 15 pin grey code signal harness. It looks like I really just need the A, B, and C altitude pin signals.

I plan to make the current transponder cable into a 'Y' cable to piggyback into the signal.
I have been told by others that this is acceptable. Also I was told that the 430W and the new encoder should not need any diodes installed inline on the harness to prevent signal dropout
Is this true?

There are a few pins that I am questioning.
On the P4001 Garmin 430W main connector:
Pin 70 is altitude D4
Since the encoder only reads to 30k and has no pin D4 I think i can leave this one blank?
Pin 60 Altitude common (ground) can i leave this blank too since power and ground are already connected to the encoder? or does it still have to be tied into encoder ground?

On the AR850 connector encoder pin 6 is simply labeled (Enable). does this need to tie into the garmin 430 in any way? What does this pin do?

thanks for any help anyone can give.
 
jeffsvan said:
I have a Narco AR850 15 pin encoder wired to a KT76 transponder tray (It has a AT165 replacement transponder installed).
This has been functioning nicely for the last 2 years.
I am now installing a 430W and need to tap into the 15 pin grey code signal harness. It looks like I really just need the A, B, and C altitude pin signals.

I plan to make the current transponder cable into a 'Y' cable to piggyback into the signal.
I have been told by others that this is acceptable. Also I was told that the 430W and the new encoder should not need any diodes installed inline on the harness to prevent signal dropout
Is this true?

There are a few pins that I am questioning.
On the P4001 Garmin 430W main connector:
Pin 70 is altitude D4
Since the encoder only reads to 30k and has no pin D4 I think i can leave this one blank?
Pin 60 Altitude common (ground) can i leave this blank too since power and ground are already connected to the encoder? or does it still have to be tied into encoder ground?

On the AR850 connector encoder pin 6 is simply labeled (Enable). does this need to tie into the garmin 430 in any way? What does this pin do?

thanks for any help anyone can give.
Click to expand...

D4 - not req'd
Pin 60 - should be fine with no connection.
Pin 6 - does not go to 430, grounding this pin enables the encoder.

Personally, I would consider getting a new encoder with serial data output, it's plug n play with the KT 76 gilliam code and 1 wire for the serial data to the 430. (I've replaced many of the old AR850's so they don't live forever) so the install would be much easier and you would have 10 ft resolution for the 430.
 
new encoder

So far this unit is working fine.
When it does go down, what make/model encoder do you recommend
for my setup. thanks
 
jeffsvan said:
So far this unit is working fine.
When it does go down, what make/model encoder do you recommend
for my setup. thanks
Click to expand...

In order of preference:
Transcal
Sandia
ACK

all of the above are available with serial output.

Also when you get done with the above re-wiring or new encoder install, you need to have the xpdr/encoder system tested to ensure it's working correctly.
 
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more....

You said: Pin 60 - should be fine with no connection.
Pin 6 - does not go to 430, grounding this pin enables the encoder.

So Pin 6 needs to be tied to ground?

I seem to remember when looking at another guys harness he
had Pin 60 tied into Pin 6 and they both pinned out to ground?

I am assuming this has something to do with 'encoder strobe' circuit?

This is the last tiny bit of my harness i need to double check and i am ready to power up :)

thanks so much for your kind replies
 
The encoder enable pin 6 must already be tied to ground if the encoder has been working.
 
even more..

YES it is connected to ground . I just went and checked.
Thanks again for your help I really appreciate it.

So the last bit of verification i need:
should Pin 60 Altitude common (ground) on Garmin 430w main connector
be tied into Pin6 going to ground. OR just leave Pin 60 completely disconnected ?

Your first thought was to leave it disconnected.
 
jeffsvan said:
YES it is connected to ground . I just went and checked.
Thanks again for your help I really appreciate it.

So the last bit of verification i need:
should Pin 60 Altitude common (ground) on Garmin 430w main connector
be tied into Pin6 going to ground. OR just leave Pin 60 completely disconnected ?

Your first thought was to leave it disconnected.
Click to expand...

It wouldn't hurt to tie 60 to ground, I'm "pretty confident" it will work if it's not, but, if you're already in there it may be a good idea to just go ahead and do it.
 
lastly..

DONE. Just went and wired it.

The only last things I can think of:

On my hand held backup mic:
There is not a specified set of pins for it on my PMS6000MS connector.
I am thinking I should piggyback it onto the Pilot Mic input Pins.
The mic has its own jack as well as built in PTT switch.

Also my external intercom speaker is grounded to airframe.
The PMA6000MS diagram is showing pins for BOTH speaker Hi and Speaker Lo.
I am hoping I wont have to run a new 2 wire cable to the speaker, and be able to just hook up speaker Hi and leave that airframe ground as-is.

Does this all sound reasonable to you?

I will test it all before I install the radio wiring permanently.

So far everything I have wired up is looking neat and tidy, and working well too! All grounds and shields were done correctly and with proper tools and materials.
 
jeffsvan said:
DONE. Just went and wired it.

The only last things I can think of:

On my hand held backup mic:
There is not a specified set of pins for it on my PMS6000MS connector.
I am thinking I should piggyback it onto the Pilot Mic input Pins.
The mic has its own jack as well as built in PTT switch.

Also my external intercom speaker is grounded to airframe.
The PMA6000MS diagram is showing pins for BOTH speaker Hi and Speaker Lo.
I am hoping I wont have to run a new 2 wire cable to the speaker, and be able to just hook up speaker Hi and leave that airframe ground as-is.

Does this all sound reasonable to you?

I will test it all before I install the radio wiring permanently.

So far everything I have wired up is looking neat and tidy, and working well too! All grounds and shields were done correctly and with proper tools and materials.
Click to expand...

"Back-up" mic/headphone jacks should go directly to the radio, just piggy backing it onto the current mic jack really doesn't do much as a "back-up".
Back-up jacks will take the intercom out of the picture in case it fails.

Not sure on the type of speaker amp the PMA6000 uses, some units use an isolated amp where the ground in not really "ground". You could ring out from the "low" output to ground and see what you get, if you get 0 resistance that you can assime the low = aircraft ground.
 
I will check for ground on that speaker low pin tonight when i work on the plane. If not I already made the new cable that will have to connect to the speaker.

The PMA6000 audio panel has a failsafe mode that defaults to Com 1 if the audio panel is shut off or blows a fuse. This was why I was thinking it was OK to hook up the handheld mic to the same pins as the headset mic jack. I wasnt going to 'piggyback' it to the headset mic jack, I wanted to connect it directly to the same pins right at the audio panel.

This has been a great learning experience for me. working with the aviation grade wires, cables, crimpers, and other tools. I used a magnifying visor and light to examine each crimp as I made them. I purchased many things from Stein and now have a complete avionics toolbox. My favorite are the handheld thermal wire strippers. I used them on almost everything.
 
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A general rule is to avoid multiple current paths, so called "single point grounding", which is why PS would like you to isolate the speaker from the airframe, and run a separate wire from Lo on the audio panel to the speaker connection. Using the airframe as a conductor may or may not allow "ground loop" noise (usually alternator whine) to be heard in your audio. Try it and see is the only way to know for sure.
 
The speaker 'Lo' pin did not go to ground. I ran a shielded pair to the speaker. That was what the PMA6000 manual called for.

So far everything else it ok.
 
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