How to remove stall switch for troubleshooting?

[M20 Ogler]

Stall horn works if it gets voltage but volts are not making it there. I’d like to take the switch out of the wing but the screws and backing nuts just spin and there is no way to get my arms in the inspection panel far enough to back up the nut w a wrench. Kinda stumped here. I can look w my cheapy iPhone endoscope but that it 

[EricJ]

I had mine out recently and it was difficult to get in and out.   I have long, skinny arms, so could just barely reach in there and use some creative means to get a tool on the nut.   This was at the expense of much of the skin on my arm from the inspection plate hole, despite taping the edge of it.

One of the nuts, at least on my J, could be held with a long extension on a socket and a wrench at the inspection plate hole.   I don't think that was possible on the other one, so I found a way to get a box-end on it and keep it captive.    My personal wingspan was just sufficient to be able to hold the tool on the nut and loosen the screw on the front at the same time.

FWIW, while I did rehab the entire switch while it was out, I suspect the issue with mine was just corrosion on the screw that held the ground wire on.    You may have the same issue on the + side screw, who knows.   I don't think that really made much difference as in my case I don't think it would have been any easier to try to clean that up in place without removing the switch.

[Prior owner]

Mooney sells an “upgraded” switch kit with a doubler that goes behind the Leading edge wing skin. The switch and the doubler will require trimming in order to fit in the location of the old switch. Also, flight testing and adjustment of the switch position with the slotted holes until it activates the horn at the appropriate IAS.

A skinny arm will definitely be needed to get it out- it’s a long reach to the leading edge from the inspection hole…

[carusoam]

There are pics around here…

Because every now and then one of these things has to come out…

There is OH info as well…. And cleaning recommendations….

and a pic of a second elbow too….  

There is some details on marking things before removing them…. Because you really want to have it go in pretty much where it came from… closely adjusted to some number of kias before the stall occurs… (10kias?)

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[M20 Ogler]

Turns out I am able to get my arm in there and reached the stall switch. I just needed to have more pain tolerance. 
 

the good news is my stall switch works just fine no need to remove it. I was able to put my fluke across the leads at the horn with the meter set to beep for continuity to ground. And I could message in morse code with the stall switch. I also have voltage at the horn with master on amd stall switch closed

so the bad news is I was wrong about the horn working fine if it gets voltage. 
 

do I need a new horn?

Edited September 24, 2021 by M20 Ogler

[Ragsf15e]

Someone more knowledgeable will be along soon, but I thought i read about it being called a “sonalert” or something like that?  Is it in your parts manual?

 I believe there’s another one for the gear warning.

[M20 Ogler]

I envy the owners of experimental aircraft. Just throw a 12volt piezoelectric buzzer in there that you can get off Amazon for $10

[MikeOH]

14 minutes ago, M20 Ogler said:

I envy the owners of experimental aircraft. Just throw a 12volt piezoelectric buzzer in there that you can get off Amazon for $10

That's exactly what it is: SONALERT SC628 piezoelectric buzzer. Available from DigiKey. Just pull your old one to confirm the part number.

[EricJ]

27 minutes ago, M20 Ogler said:

I envy the owners of experimental aircraft. Just throw a 12volt piezoelectric buzzer in there that you can get off Amazon for $10

 

7 minutes ago, MikeOH said:

That's exactly what it is: SONALERT SC628 piezoelectric buzzer. Available from DigiKey. Just pull your old one to confirm the part number.

Yup.   There is no FAA-PMA source for the Sonalerts, so no need to pay AMUs for it, just regular plebian prices.    A web search on Mallory SC628 or Sonalert SC628 gets a lot of sources anywhere from $14-$20 ea.   You can get a 2-pak on Amazon for $40.

 

 

[A64Pilot]

For those concerned about the legality of using a non PMA source for parts, this AC may help you, for switches and relays etc it’s particularly helpful as those were almost always outsourced by most any manufacturer.

https://www.faa.gov/documentlibrary/media/advisory_circular/ac_23-27.pdf

[carusoam]

The cool thing about it not being the switch… the switch is hard to access….

The uncool thing about it being the Sonalert… the Sonalert is hard to access….   

The ceiling typically comes out for that….

But, since you are in there… get ready to check everything while the ceiling is out…

It may be the wires going to the Sonalert…. So don’t rush to get the ceiling down too quickly….

PP thoughts only, not a mechanic…

Best regards,

-a-

[M20 Ogler]

My current stall horn is located behind the instrument panel attitude indicator bolted to the firewall. Confirmed by putting my ohm meter in series with it to chassis ground and then closed the stall switch on the wing. 
 

edit: I used the audio continuity test setting on my ohm meter and put it in place of the stall horn in the circuit to test the stall switch. 

8 hours ago, carusoam said:

The cool thing about it not being the switch… the switch is hard to access….

The uncool thing about it being the Sonalert… the Sonalert is hard to access….   

The ceiling typically comes out for that….

But, since you are in there… get ready to check everything while the ceiling is out…

It may be the wires going to the Sonalert…. So don’t rush to get the ceiling down too quickly….

PP thoughts only, not a mechanic…

Best regards,

-a-

 

Edited September 27, 2021 by M20 Ogler

[Guest]

Is it one of these?

[M20 Ogler]

1 minute ago, M20Doc said:

Is it one of these?

Yes that’s it 

[Guest]

A friend of mine has one in his Piper Arrow.  He took it apart and cleaned and adjusted it.

Clarence

[carusoam]

2 minutes ago, M20Doc said:

A friend of mine has one in his Piper Arrow.  He took it apart and cleaned and adjusted it.

Clarence

Way cool Clarence!

See if you made @M20 Ogler’s day complete!

As always… thanks for sharing your detailed aviation knowledge!
 

 

Best regards,

-a-