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  #1  
Unread 06-05-24, 05:20 PM
Melliot Melliot is offline
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Need Pic of trim/ap wiring plug

We bought a 77' P337, and AP hasn't worked. Just trying to track down the issue. First thing I've found is this plug and circuit board with 3 wires broke off of it as the yoke was hitting the wiring harness. I was hoping someone could take a picture of there's so I know what color wire goes to what point on the board. Only 3 wires are broke on mine. The wiring diagram in the manual doesn't specify nor does the Cessna 400A manual. Just need a Pic please. I'll troubleshoot more after getting all 3 wires soldered back.
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File Type: jpg 20240605_133659.jpg (70.3 KB, 179 views)
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  #2  
Unread 06-05-24, 07:47 PM
RandyArizona RandyArizona is offline
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Quote:
Originally Posted by Melliot View Post
We bought a 77' P337, and AP hasn't worked. Just trying to track down the issue. First thing I've found is this plug and circuit board with 3 wires broke off of it as the yoke was hitting the wiring harness. I was hoping someone could take a picture of there's so I know what color wire goes to what point on the board. Only 3 wires are broke on mine. The wiring diagram in the manual doesn't specify nor does the Cessna 400A manual. Just need a Pic please. I'll troubleshoot more after getting all 3 wires soldered back.
What you are looking for, (I believe), is the Avionics service/parts manual.
D4548-2-13
I have a set for the 1974-1976 models.
If you give me a little more information, I may be able to track down the pages that you need. (the 76-77 models were almost identical)
I will need autopilot model.
The plug and circuit you are looking at, is the board that the wiring goes thru / to the yoke, and then to the items, (ie, ap disconnect/map light/ptt switch)
Let me know, I will attempt to photocopy the pages you need.
Regards,
Randy
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  #3  
Unread 06-05-24, 08:31 PM
RandyArizona RandyArizona is offline
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The item you show in the picture, is listed at
parts manual
FIG 94A
Items are
36 3421-0000 connector socket
43 S1961-1-0 Housing
44 1570306-1 board-circuit
45 3428-1002 header

From my quick look at the avionics manual, and wiring diagrams,
it appears, the mechanic chooses the wires he uses from the connector and header. I don't know. The manual is vague.
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  #4  
Unread 06-06-24, 06:04 AM
Melliot Melliot is offline
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Yes, that seems to be what I need. I have a 1977 T337G. Cessna 400A autopilot. Not sure if those wires would effect the ap or not. Electric trim still works. Thanks for any help!


Quote:
Originally Posted by RandyArizona View Post
What you are looking for, (I believe), is the Avionics service/parts manual.
D4548-2-13
I have a set for the 1974-1976 models.
If you give me a little more information, I may be able to track down the pages that you need. (the 76-77 models were almost identical)
I will need autopilot model.
The plug and circuit you are looking at, is the board that the wiring goes thru / to the yoke, and then to the items, (ie, ap disconnect/map light/ptt switch)
Let me know, I will attempt to photocopy the pages you need.
Regards,
Randy
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  #5  
Unread 06-06-24, 06:05 AM
Melliot Melliot is offline
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Yeah, that's the kicker. I may just have to rewire the whole thing or see if those wires that are broke do anything anyway. I was hoping it was standard wiring and I just didn't have the diagram.
Quote:
Originally Posted by RandyArizona View Post
The item you show in the picture, is listed at
parts manual
FIG 94A
Items are
36 3421-0000 connector socket
43 S1961-1-0 Housing
44 1570306-1 board-circuit
45 3428-1002 header

From my quick look at the avionics manual, and wiring diagrams,
it appears, the mechanic chooses the wires he uses from the connector and header. I don't know. The manual is vague.
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  #6  
Unread 06-06-24, 09:17 AM
RandyArizona RandyArizona is offline
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Give me a few hours, we’ll see what we can do for you.
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  #7  
Unread 06-06-24, 02:01 PM
rustymwm rustymwm is offline
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Name:  400A Wiring Diagram.PNG
Views: 331
Size:  386.5 KB

The attached files are from the 77-78 Avionics manual D4580-2-13.

In order for the autopilot to power on, pin A on the control unit must be grounded. It is certainly possible that one of your broken wires is the cause of your dead autopilot.

Since your electric trim is functioning, pin D on the trim switch is properly grounded. Thus, the problem could be: 1) the autopilot disconnect switch on the yoke is not closed, 2) the g-switch is open, or 3) there is a fault in the associated wiring - probably one of your broken wires.

As you can see on the diagram, the color code for the wire on your circuit board is yel/grn (1). I could not identify this wire in your picture. If you cannot identify the wire based on the color code, an alternative method would be to use a multi-meter. With the AP powered off, there should be little to no voltage on the wire. With the AP powered on, there should be near 25V on the wire. Note: You will have to hold the AP power switch "on" when you check the powered on state of the wire. If the switch stays on by itself, then forget all of the above - it is not the problem.

As for the other 2 wires, since the pitch trim works, they could be related to either the mic push-to-talk switch or the map light on the yoke.

Hope that helps.
Attached Files
File Type: pdf 400A Wiring Diagram.pdf (645.1 KB, 161 views)
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  #8  
Unread 06-06-24, 02:08 PM
RandyArizona RandyArizona is offline
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I was beaten to it.
Attached are what I have.
"like a chinese buffet, take what you want, and leave the rest..."
Attached Files
File Type: pdf 06161601.PDF (259.2 KB, 161 views)
File Type: pdf 06161602.PDF (869.6 KB, 150 views)
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  #9  
Unread 06-06-24, 02:09 PM
RandyArizona RandyArizona is offline
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Last pdf file of the autopilot
Attached Files
File Type: pdf 06161603.PDF (666.7 KB, 181 views)
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  #10  
Unread 06-07-24, 04:20 PM
Melliot Melliot is offline
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You all are awesome! Thanks and I'll see what I find when I get home.

Quote:
Originally Posted by rustymwm View Post
Attachment 3076

The attached files are from the 77-78 Avionics manual D4580-2-13.

In order for the autopilot to power on, pin A on the control unit must be grounded. It is certainly possible that one of your broken wires is the cause of your dead autopilot.

Since your electric trim is functioning, pin D on the trim switch is properly grounded. Thus, the problem could be: 1) the autopilot disconnect switch on the yoke is not closed, 2) the g-switch is open, or 3) there is a fault in the associated wiring - probably one of your broken wires.

As you can see on the diagram, the color code for the wire on your circuit board is yel/grn (1). I could not identify this wire in your picture. If you cannot identify the wire based on the color code, an alternative method would be to use a multi-meter. With the AP powered off, there should be little to no voltage on the wire. With the AP powered on, there should be near 25V on the wire. Note: You will have to hold the AP power switch "on" when you check the powered on state of the wire. If the switch stays on by itself, then forget all of the above - it is not the problem.

As for the other 2 wires, since the pitch trim works, they could be related to either the mic push-to-talk switch or the map light on the yoke.

Hope that helps.
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