JohnB

Nav light on - autopilot shutoff problem

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This is a strange one, but it’s a shot in the dark to see if anyone else has had a similar problem. A few months ago, my autopilot kfc 150 shutoff in flight for no reason I could identify then and would not come back on. Replaced the ap disconnect switch with a new one and later realized that switch wasn’t faulty, but the problem was, when I turn my nav light switch  on, my autopilot disconnects. Doesn’t happen with any other lights or switches, even if I turn all other switches on other than the nav switch. Had led nav lights installed around 6 years ago, and no major avionics work in the last year.

Was wondering for any electrical person out there might have any thoughts? Or if by some odd chance, someone else has had a similar problem? Shop is looking for a chaffed wire now. Looking for ideas rather than trying to replace everything ($$$$) and see if it works later approach. 

 

 

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I know the nav light dims the gear down light on the annunciator on  the M20M, maybe there's a voltage drop when it happens.

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39 minutes ago, LANCECASPER said:

I know the nav light dims the gear down light on the annunciator on  the M20M, maybe there's a voltage drop when it happens.

Interesting thought. As my nav light turns on, unlike all other rocker switches, it changes the dimming on all of my annunciator and panel lights. I wonder if it also dims the annunciators on my kfc 150 and perhaps that connection is faulty... Hmmm good food for thought.. ill look into it. thanks!

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1 hour ago, JohnB said:

Interesting thought. As my nav light turns on, unlike all other rocker switches, it changes the dimming on all of my annunciator and panel lights. I wonder if it also dims the annunciators on my kfc 150 and perhaps that connection is faulty... Hmmm good food for thought.. ill look into it. thanks!

I would check the bus voltage with the nav lights on and off. It sounds like there may be a problem with the nav lights causing a voltage drop. I don’t think the nav lights should affect the panel lights. The autopilot might just be more sensitive to voltage than the other avionics.

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30 minutes ago, PT20J said:

I would check the bus voltage with the nav lights on and off. It sounds like there may be a problem with the nav lights causing a voltage drop. I don’t think the nav lights should affect the panel lights. The autopilot might just be more sensitive to voltage than the other avionics.

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Got it.. I like this voltage drop idea that you and @LANCECASPER have.. Ill get my avionics shop to check it Monday. Thanks!!

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14 hours ago, JohnB said:

Interesting thought. As my nav light turns on, unlike all other rocker switches, it changes the dimming on all of my annunciator and panel lights. I wonder if it also dims the annunciators on my kfc 150 and perhaps that connection is faulty... Hmmm good food for thought.. ill look into it. thanks!

Turning on the NAV lights does dim all the other lights, deliberately, as it assumes night.  It also enables the dimmer rheostats in the lower right hand panel.  Try turning the rheostats full ON to see if it makes any difference.  Older wiring can create some problems.  My plane is in maintenance now for a problem with the prop deice.  Turns out it was a broken ground wire.  It took a number hours to find the problem.  I'm looking forward to getting the plane back this week--maybe.  Turns out I'm in the group in California that is supposed to self isolate.  Thank you, John, for your input on the other thread.

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2 hours ago, donkaye said:

Turning on the NAV lights does dim all the other lights, deliberately, as it assumes night.

Some models do that, true. That design can lead to issues and it is worth checking to see if a part of the autopilot system is (improperly) powered by the dimmer bus.
 
Last week I flew a plane with a recently-installed uAvionix tailbeacon.  The new ADS-B hardware is powered by the Nav light circuit.  So the Nav lights have to be on all the time, which makes the annunciator lights impossible to read in daylight.   

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12 hours ago, donkaye said:

Turning on the NAV lights does dim all the other lights, deliberately, as it assumes night.  It also enables the dimmer rheostats in the lower right hand panel.  Try turning the rheostats full ON to see if it makes any difference.  Older wiring can crea

Turns out I'm in the group in California that is supposed to shelter in place.  Thank you, John, for your input on the other thread.

Great ideas and thank you. Hope the other thread info helps too 

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I Typically fly with all the nav lights on in daylight...

The M20R dims the annunciator panel automatically... making the green gear down light hard to see in daylight...

The auto-dimming based on the nav lights being on was a bit of a surprise...

maybe this is a surprise for someone else...?

Best regards,

-a-

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On 3/16/2020 at 9:02 PM, carusoam said:

I Typically fly with all the nav lights on in daylight...

The M20R dims the annunciator panel automatically... making the green gear down light hard to see in daylight...

The auto-dimming based on the nav lights being on was a bit of a surprise...

maybe this is a surprise for someone else...?

Best regards,

-a-

Piper came up with a “clever” nav light switch. It’s at the end of travel of the thumbwheel rheostat for the panel lights. You cannot turn on the panel lights without turning on the nav lights. Pretty clever way to keep from forgetting to turn the nav lights on. Turning on the nav lights also dims the annunciator lights. 

During a daytime checkout in a Seminole, the instructor thought we should shut down an engine and land with it feathered. He didn’t want me to put the gear down until we had the runway made, so we put it down on one mile final. No green lights. Low, slow, didn’t want to go around on one engine. Quickly figured someone had turned the panel lights down all the way but not clicked off the nav lights. So, yep, I’ve been there.

I didn’t know Mooney also dims the panel lights with the nav lights on late models; my J doesn’t do that and I cannot recall another airplane that does that. Seems kind of silly unless the later planes have really bright bulbs or something.

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On 3/15/2020 at 10:46 PM, JohnB said:

This is a strange one, but it’s a shot in the dark to see if anyone else has had a similar problem. A few months ago, my autopilot kfc 150 shutoff in flight for no reason I could identify then and would not come back on. Replaced the ap disconnect switch with a new one and later realized that switch wasn’t faulty, but the problem was, when I turn my nav light switch  on, my autopilot disconnects. Doesn’t happen with any other lights or switches, even if I turn all other switches on other than the nav switch. Had led nav lights installed around 6 years ago, and no major avionics work in the last year.

Was wondering for any electrical person out there might have any thoughts? Or if by some odd chance, someone else has had a similar problem? Shop is looking for a chaffed wire now. Looking for ideas rather than trying to replace everything ($$$$) and see if it works later approach. 

I have dealt with multiple issues like this.

 

  Bob Weber

Autopilot Consulting

webairconsulting.com

On 3/15/2020 at 10:46 PM, JohnB said:

 

 

 

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On 3/16/2020 at 10:02 PM, carusoam said:

I Typically fly with all the nav lights on in daylight...

The M20R dims the annunciator panel automatically... making the green gear down light hard to see in daylight...

The auto-dimming based on the nav lights being on was a bit of a surprise...

maybe this is a surprise for someone else...?

I leave my Nav lights on all the time. Even when she's parked in the hangar. It's harder to close up the hangar and leave the Master on, with the Nav lights lighting up the place.

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There may have been a hint...   like a screw fell on the floor...

-a-

 

Bob’s pic above with my edits...

2C349453-5F61-4CB8-9861-02A7F922FAEF.jpeg

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13 hours ago, Bob Weber said:

This is what we found the last time I heard this story...

 

A screw out?  Not sure that  could cause the autopilot to disconnect only when the nav lights are turned on and have both work fine independently. Or can it?  If that's true, where is this array? 

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Each of these types of problems have their unique causes, I call them "new and improved". I doubt we will find anything this severe with this issue, but we can locate it with a voltmeter quicker than a checkbook. Cheaper too! How much was that disconnect switch? Did anyone troubleshoot, or just shotgun parts?

 

Bob Weber

Autopilot consulting

webairconsulting.com

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18 hours ago, carusoam said:

There may have been a hint...   like a screw fell on the floor...

-a-

 

Bob’s pic above with my edits...

2C349453-5F61-4CB8-9861-02A7F922FAEF.jpeg

Anthony doesn't miss a thing . . . sharp as a marble!

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7 minutes ago, LANCECASPER said:

Anthony doesn't miss a thing . . . sharp as a marble!

The screw was more visible in another shot, it was lodged a row below and close to the buss. It was located within an hour or two of the initial evaluation call, from Australia...

Bob Weber

Autopilot Consulting

webairconsulting.com

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Nice all,

 

it’s amazing the breadth of knowledge on this board. Impressive diagnostic @Bob Weber from such a distance! Thank you all. My installer found the problem, it was a diode that had gone bad that was related to my TXi install. Works like it should now. Thank again everyone for the tips! 

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Great pirep for Mr. Weber!

Thanks for posting the details.

Best regards,

-a-

 

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