Jump to content

Recommended Posts

I have a 1981 M20J and I've replaced one or more of the micro switches twice and I've replace the entire switch with new, twice...over the past 8 years.  I find it hard to believe this is normal and I'm convinced there is something else going on that causing this ongoing problem.

Thoughts?

Thanks in advance for your feeback

Rick

Link to comment
Share on other sites

I have a 1981 M20J and I've replaced one or more of the micro switches twice and I've replace the entire switch with new, twice...over the past 8 years.  I find it hard to believe this is normal and I'm convinced there is something else going on that causing this ongoing problem.

Might want to post a picture of your switch so we know what you have.


Tom
Link to comment
Share on other sites

2 hours ago, skykrawler said:

What symptom resulted in the replacement?

Electrical or mechanical?  In other words what is the ongoing problem? Is it intermittent?

Which autopilot?

 It worked fine last week and did not work during pre flight yesterday, with no symptoms leading up to the failure.

KFC200

Link to comment
Share on other sites

The last time I had a problem with this on my 81 J it turned out to be that the raised area on the thumbpiece was worn down so that it didn't make proper contact with the microswitch.  Mine has been trouble free for many years now but I dont use it a lot.

Link to comment
Share on other sites

Is it possible that some of these switches are plastic and some are metal?

Both parts of my KAP150’s switch look metalish in comparison to Zu’s... I also have both switches in black, not that burnt orangish color...

I have put untold stress on mine... during a few Go-Arounds... over the years...

Powering up, trimming down, flying the plane... it is a challenge to actually feel the switch...

If one is plastic, it might not be handling the stress of a fully up-trimmed go-around...? :)

PP thoughts only, not a CFI...

Best regards,

-a-

Link to comment
Share on other sites

On 4/8/2019 at 1:13 AM, carusoam said:

Is it possible that some of these switches are plastic and some are metal?

Both parts of my KAP150’s switch look metalish in comparison to Zu’s... I also have both switches in black, not that burnt orangish color...

I have put untold stress on mine... during a few Go-Arounds... over the years...

Powering up, trimming down, flying the plane... it is a challenge to actually feel the switch...

If one is plastic, it might not be handling the stress of a fully up-trimmed go-around...? :)

PP thoughts only, not a CFI...

Best regards,

-a-

I can't answer the plastic versus metal question...either way, its some of the most expensive metal or plastic I've ever purchased before

  • Like 1
Link to comment
Share on other sites

I don’t know if my experience is either relevant or helpful, but about 6 months ago my trim quit working.  I figured it was a bad switch but it turned out the switch was simply slightly out of adjustment.  The micro switch just needn’t to be adjusted, not replaced.  Works fine.

Link to comment
Share on other sites

On 4/7/2019 at 10:14 AM, Zulee said:

 It worked fine last week and did not work during pre flight yesterday, with no symptoms leading up to the failure.

KFC200

So I guess you are saying it did nothing during the pre-flight.  And I will assume your Trim power switch on the panel is ON.

With the aircraft on the ground and not running.....as you toggle each of the two switches you should be able hear a click in each direction.  This sound is the contacts transferring.  Verify that you hear that sound on both.  If not there is a mechanical problem with switch.

Here is how to verify the trim switch operation and connections.

Avionics on, autopilot powered but not engaged.    Toggle only the red side of trim switch each direction and check that the trim clutch engages by moving the wheel manually and feeling the resistance.  If not, it could be a power problem related to the AP disconnect button.   If the clutch engaged both directions proceed.....

Engage autopilot.  Push both trim buttons up - AP should disconnect.  Engage autopilot, push both switches down, AP should disconnect.

If this all works it is not a problem with the switches or connections to the AP.  If it doesn't it could be a problem with the switches or the wires that routes through the wheel/column.   The wires undergo a certain amount of flex where they emerge from the control tube.

Attached is the TRIM PREFLIGHT CHECK. for the 150 which should be similar.

trim-preflight.pdf

Link to comment
Share on other sites

  • 2 months later...

It's been a few weeks but here is the follow up on the trim switch.  

I tracked down a new one (wow, are they expensive) but before we replaced the old one we wanted to do a little more troubleshooting.  As we began the process, it was first believed to be an electrical issue...turns out, it was not.  As RobertE mentioned above, it turned out to be a mechanical issue and to answer Carusoam's question...the switch is plastic with metal tabs that wrap around each micro switch, which is what actually depresses the little red (plastic) button on the micro switch itself.

After removing the switch and using a very bright light we were able to observe the mechanics of how this plastic/metal conglomeration worked.  In essence these little micro switches have very little tolerance in terms of how hard they can be depressed.  We noticed that 2 of the 3 tabs pushed "just enough" to hear the switch click and you could still see about half of the red button when fully depressed.  However, on the 3rd micro switch depressed so far there was little to no red showing and the first indication that maybe this was our problem or at least another area to explore a little deeper.

The switch housing itself has two screws that run laterally through the housing and through the three micro switches.  The screw holes are perfectly round so initially we thought there was no way to "adjust" the amount of downward pressure on that 3rd micro switch.  So we removed the two screws so we could get a closer look at how this puppy goes together and thanks to all the wires soldered in place, the three  micro switches slid out in a cluster.  Once we removed the switches from the housing we noticed a little metal plate on vertical side of the housing that had elongated holes.  SCORE!!!!!

While the metal plates seemed to be glued into place, with just a little force they easily broke loose and we were able to position them enough to offset the downward pressure on the micro switch button.  Once we made this adjustment we could hear the click and see about half of the little red micro switch button as we saw with the other two.  

Call it blind luck or absolute curiosity, but once we made adjustments to the plate and reassembled and installed the old switch back in place...it worked like a charm.

I'm not sure the situation/solution we found with my switch to be consistent with others posting trim switch issues, but it's worth a look-see and costs nothing versus hundreds of dollars for a new switch that you may not need.

 

  • Like 3
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.