King Autopilot Disconnect Switch

[Steve W]

So, as it apparently happens frequently my King AP disconnect switch went out on my KAP 150. This is not asking for help, it's been replaced, but I wanted to provide the part number that might have been used for the replacement and what the old one looked like.

If I were to have ordered the replacement part from Mouser.com it would have been part number 633-MB2061SS1W01CC and it would have looked like the below(new switch on the left). (check the cap size before ordering, there is a large cap -CC and a small cap -BC, some other sites have reported the small cap, in reality it doesn't matter as you can reuse the cap)

But the most telling thing is what the old one looked like when disassembled. Notice the contact for the trim power side of the switch is basically totally gone as they run way too much power through it and using it to disconnect causes an arc. So, I've now learned(about $300 too late) to never use the Yoke disconnect switch except in an emergency and just disconnect from the autopilot front panel or by engaging the manual electric trim which might also be safe for the switches, although that unit is even more expensive to replace or rebuild.

Edit: and one other thing I learned is that it's a fully sealed switch, so spraying it with contact cleaner probably won't hurt to try and make it work again, but if it still doesn't work the problem still may be the switch as there's a good chance none of the cleaner actually got inside.

[carusoam]

Nice report, Steve!

Best regards,

-a-

[StevenL757]

I agree...nice PIREP.  The manual electric (split) trim switch sitting next to that red push-button are ~$875, so thank goodness you don't have to replace that bugger.  I may pick up a few of these from Mouser just in case.  I admit I'm guilty of disconnecting the AP more with that button than I am reaching down to the panel, so that's a habit I'll work on changing straight away.

Steve

[PTK]

Does the one from Mauser carry an STC or PMA?

[jetdriven]

Does it need one? I see the same part number on both.  Standard part. 

Edited February 2, 2018 by jetdriven

[PTK]

I don't know. I was simply asking if the 7$ Mauser switch had STC or PMA. Does a switch that's an intergral part of the flight control system, i.e. autopilot, in a certified ac need to be? If I was a betting man I would certainly think so but I'm not an expert and it's not my airplane.

 

[Steve W]

Luckily the FAA Approved Repair station reviewed the part and based on their findings that it was identical to the original part used it to do the repair and then did the necessary testing to determine the system was functional and signed it off for return to service. And really, NKK who makes the switches didn't have a PMA when they made the original part, and don't have a PMA now.

[jaylw314]

IIRC, electronic parts that are standard, e.g. have a part number, can be replaced with another without separate PMA's or meeting any TSO's.

[Maxim O]

Thank you Steve! I've run into the same problem with the switch and you've help me with this report a lot.

Best!

[carusoam]

Welcome aboard, Maxim!

Great thank-you note.

@Steve W did a great Job on that one.

Best regards,

-a-

[drb930]

Subscribed

[Marek7]

I was always told to use to disconnect switch on the yoke to avoid using the one on the king autopilot controller because they have a magnetic micro switch that fails with use.

Regards,

Mark

[Steve W]

6 hours ago, Marek7 said:

I was always told to use to disconnect switch on the yoke to avoid using the one on the king autopilot controller because they have a magnetic micro switch that fails with use.

 

I believe that's the KFC 200, not the 150. The 150 just has a normal button on the autopilot control head.

[Scottknoll]

On 2/2/2018 at 1:51 PM, Steve W said:

So, as it apparently happens frequently my King AP disconnect switch went out on my KAP 150. This is not asking for help, it's been replaced, but I wanted to provide the part number that might have been used for the replacement and what the old one looked like.

If I were to have ordered the replacement part from Mouser.com it would have been part number 633-MB2061SS1W01CC and it would have looked like the below(new switch on the left). (check the cap size before ordering, there is a large cap -CC and a small cap -BC, some other sites have reported the small cap, in reality it doesn't matter as you can reuse the cap)

But the most telling thing is what the old one looked like when disassembled. Notice the contact for the trim power side of the switch is basically totally gone as they run way too much power through it and using it to disconnect causes an arc. So, I've now learned(about $300 too late) to never use the Yoke disconnect switch except in an emergency and just disconnect from the autopilot front panel or by engaging the manual electric trim which might also be safe for the switches, although that unit is even more expensive to replace or rebuild.

Edit: and one other thing I learned is that it's a fully sealed switch, so spraying it with contact cleaner probably won't hurt to try and make it work again, but if it still doesn't work the problem still may be the switch as there's a good chance none of the cleaner actually got inside.

Steve W, what were the symptoms when you had this happen? I used the Red disconnect switch the other day, and lost ability for electric trim and autopilot. It happened immediately after using the red button, so I'm assuming I may have the same issue you had.

 

Thanks,

Scott

[N201MKTurbo]

I would verify that the disconnect relay has a flyback diode on its coil. If it doesn't, I would add one.

That's what usually causes that kind of damage on switch contacts that actuate a relay. It actually arcs when you release the switch. 

[Steve W]

1 hour ago, N201MKTurbo said:

I would verify that the disconnect relay has a flyback diode on its coil. If it doesn't, I would add one.

That's what usually causes that kind of damage on switch contacts that actuate a relay. It actually arcs when you release the switch. 

Relay?

There is no relay. It's directly powering the servos. It's under-rated and almost certainly getting the inductive kickback when it disengages the servos. If they had actually used a relay we'd not have this thread, especially if they put a diode on it. I'd have put a scope on it but I really didn't care that much.

 

1 hour ago, Scottknoll said:

Steve W, what were the symptoms when you had this happen? I used the Red disconnect switch the other day, and lost ability for electric trim and autopilot. It happened immediately after using the red button, so I'm assuming I may have the same issue you had.

In mine the Autopilot(KAP-150) wouldn't power up and would just beep repeatedly until you pulled the breaker. Sometimes it would re-engage when the breaker was reconnected but eventually that even stopped working.

 

[robertcor]

is the housing to pull out the a/p disconnect switch easy to open up ?

any special tricks or tools ?

 

thanks for the reply,  robert cordero   10/8/21

[PT20J]

6 hours ago, robertcor said:

is the housing to pull out the a/p disconnect switch easy to open up ?

any special tricks or tools ?

 

thanks for the reply,  robert cordero   10/8/21

Housing is held on with a couple of small screws. The switch cap screws onto the shaft. The silver bezel nut screws onto the switch. Unscrew cap the bezel to remove switch.

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[carusoam]

Welcome aboard Robert…

Share what you learn with your avionics guy… 

PP thoughts only, not a mechanic…

Best regards,

-a-