Urgent help needed - electrical trim switch (yoke)

[NicoN]

We actually have trouble with the ectrical trim switch in our M20K /S/N 25-385).

For a qhile we have seen the Fuse/switch for the electrical trim trapping some times.

Today, I opened the yoke to change the MIC-button and almost all of the cables were torn off ( or I gave some wires the rest:-(   )

So, I was looking on my printout of the electrical scheme and  - I did not find this switch ( shame on me).

On top comes, that my PDF of the maintencance manual is corrupt and no more readable

So, please:

1. Is the PDF of Maintenance manual available somewhere

2. Has someone an idea of where the trim switch is located on the electrical scheme and how that switch works ?

 

I think , it is not part of the A/P (which is a Century 21), as this A/P has no ALT-hold function.

Thank you a lot

[OR75]

So what altitude hold system is it ?

[NicoN]

Actually our M20k has no ALT-hold originally. We have an S-TEC 60 PSS, but this guy does not affect Elevator-Trim

This switch has the up/down function and by pushing it activates a clutch. So, normally you can hear the trim motor running by activating the up or down function, but the trim wheel does not move at all. This happens only if you push it down also.

 

 

Edited July 24, 2020 by NicoN

[carusoam]

Nico,

See if you can post a pic of the switch...
 

That will get a lot of eyeballs on it...

Trim switches, very often are supplied by AP manufacturers...

BK switches are terrible e expensive....

Aircraft spruce may have something your mechanic will approve for use....

Best regards,

-a-

[GeeBee]

For S-Tec autopilots

https://www.aircraftspruce.com/catalog/elpages/trimswitch11-15410.php

 

 

[Missile=Awesome]

I have the System 60 PSS and it is NOT a split trim on yoke.  It is just the standard elevator trim.  Who made/makes the standard yoke trim switch you see on Mooney aircraft?

Edited July 24, 2020 by Missile=Awesome
Added Photo

[OR75]

6 minutes ago, Missile=Awesome said:

I have the System 60 PSS and it is NOT a split trim on yoke.  It is just the standard elevator trim.  Who made/makes the standard yoke trim switch you see on Mooney aircraft?

That’s weird because I have a 60PSS and it is a split trim on the yoke 

the original part is made of plastic that becomes brittle over time and breaks. It is not cheap to replace and the Cignet part above made of aluminum is a great replacement.

the 2 switches are 3-poles switches and, if the plastic part is in good shape, can be replaced for cheap if you have the wiring diagram and are good with soldering. Note that the Cignet part above includes the 2 switches (they are the red color switches) 

 

[Missile=Awesome]

1 hour ago, OR75 said:

That’s weird because I have a 60PSS and it is a split trim on the yoke 

the original part is made of plastic that becomes brittle over time and breaks. It is not cheap to replace and the Cignet part above made of aluminum is a great replacement.

the 2 switches are 3-poles switches and, if the plastic part is in good shape, can be replaced for cheap if you have the wiring diagram and are good with soldering. Note that the Cignet part above includes the 2 switches (they are the red color switches) 

 

What is the purpose in having the switch “split”?

[Rwsavory]

4 minutes ago, Missile=Awesome said:

What is the purpose in having the switch “split”?

So that a switch failure won't result in a trim runaway.

[PTK]

2 hours ago, Missile=Awesome said:

What is the purpose in having the switch “split”?

In the BK ap the left side powers the trim servo clutch while the right side controls the servo motor direction of travel. Both must engage in order to operate the electric trim in the desired direction.

[GeeBee]

4 hours ago, Missile=Awesome said:

I have the System 60 PSS and it is NOT a split trim on yoke.  It is just the standard elevator trim.  Who made/makes the standard yoke trim switch you see on Mooney aircraft?

Seen them on King Air's with Century A/P. Should be common enough.

 

 

[laytonl]

I Believe the switch wiring diagram for the Century is in the autopilot manual.  Lee

[Missile=Awesome]

1 hour ago, GeeBee said:

Seen them on King Air's with Century A/P. Should be common enough.

 

 

Mine works fine.  Guess I am cheating death with a runaway trim without the split control...who knew?...

[NicoN]

it is exactly this siwtch.

The switch is perfect, I think.

But cables are torn off, so I need some help what the switch does and which cables are there.

There is on cable coming from the TRIM INterrupt button which has 12 V on it

The button has no splited button.

It contains 3 little switches. 2 for up/down and 1 for the clutch

 

Edited July 25, 2020 by NicoN

[OR75]

12 hours ago, NicoN said:

it is exactly this siwtch.

The switch is perfect, I think.

But cables are torn off, so I need some help what the switch does and which cables are there.

There is on cable coming from the TRIM INterrupt button which has 12 V on it

The button has no splited button.

It contains 3 little switches. 2 for up/down and 1 for the clutch

 

If it is a century switch, the century website has the wiring diagram for the different trim switches. But honestly, you may want to have a shop look at it and redo the wiring for you. 
it is too risky to just guess what you have 

[bradp]

Look for a post by me with troubleshooting trim circuit breaker a few years ago.  When I resoldered my leads I drew out a little  wiring diagram. 
 

here it is 

https://mooneyspace.com/topic/19611-trim-cb-popping/?do=findComment&comment=375210

 

somewhere I have pictures I took when I was resoldering the switch I’ll see if I can find them.  
 

use this as reference only, of course.  A hand drawn picture by someone on the internet isn’t approved data. 

[NicoN]

Thank you for the picture.

As far as I understand, the trim switch has 2 functions:

1,. It activates the clutch (middle switch)

2. It works as a voltage reversing switch. Normally (doing nothing), both output lines are grounded. Operating the lever in one direction or the other just switches the posles.

It is a typical schematic called "H" to reverse DC motors

 

My problem  is not the switch, it is that all cables are torn off. So, I have 6 cables and not an excat idea what they do.

I have ...

2 cables (red/white and purple white) connected to 12V via Elev trim C/B

1 cable (yellow white) which seems to be connected to aircraft GND

1 cable (blue/white) which activates the clutch if you connect it to one of the 12 V cables

1 cable (black/white) going to the Trim Intterupt button with a little blue wire coming back from there. It has 12 V, but is not strong enough to power the clutch

2 cables which I was thinking is the DC motor itself.

But the motor does not activate, it is simply silent. And also, I do not find a resistance between the 2 cables (unlimited) For a DC motor I would expect a low resistance between them

 

Any idea of how the switch (and especially the cbles work ?

[OR75]

9 hours ago, NicoN said:

Thank you for the picture.

As far as I understand, the trim switch has 2 functions:

1,. It activates the clutch (middle switch)

2. It works as a voltage reversing switch. Normally (doing nothing), both output lines are grounded. Operating the lever in one direction or the other just switches the posles.

It is a typical schematic called "H" to reverse DC motors

 

My problem  is not the switch, it is that all cables are torn off. So, I have 6 cables and not an excat idea what they do.

I have ...

2 cables (red/white and purple white) connected to 12V via Elev trim C/B

1 cable (yellow white) which seems to be connected to aircraft GND

1 cable (blue/white) which activates the clutch if you connect it to one of the 12 V cables

1 cable (black/white) going to the Trim Intterupt button with a little blue wire coming back from there. It has 12 V, but is not strong enough to power the clutch

2 cables which I was thinking is the DC motor itself.

But the motor does not activate, it is simply silent. And also, I do not find a resistance between the 2 cables (unlimited) For a DC motor I would expect a low resistance between them

 

Any idea of how the switch (and especially the cbles work ?

The color code of a wire will not indicate where it should be connected. It can only help you trace where it is coming from 

i don’t think there is such thing as a clutch in a trim switch 
Again, someone needs to positively identify what trim switch You have 

[bradp]

@NicoN

can you crawl under the panel and shoot a picture of your relay and crawl I. The empennage and shoot a picture of your trim motor switch.  Data plates would be very helpful. 

[NicoN]

@OR75: Correct, the switch has not clutch. But normally, if you press the Actuator (on the switch), then a clutch in the trim motor activates and you cannot move the trim wheel by hand.

So, again: Move the trim switch to the up or down position, then the trim motor runs. But your trim wheel still does not move as the clutch is open. Press the trims switch AND move to up/down - then the motor runs an moves the trim wheel.

At the moment, I can close the clutch without the switch just by applying 12V to the bl/wt-wire. Now, I cannot move the trim wheel by hand.

But the second function - activating the motor with or without the clutch closed, dosent work.

 

ABout cabling: The cables ending in the yoke where the trim switch was connected, have colour codes, like blue/white or red/white and so on. Mooney uses these all white cables but with number codes printed on them.

This may be a sign, that this trim switch was added later and belongs maybe to the S-TEC 60 PSS.

 

 

[NicoN]

@bradp: 

  I have exact this motor and also a relay box which seems to be mounted close behind the big hole in the fueslage.

Any ideas of how this stuff works exact?

I did not find wring drawings for this on centuryflight nor on S-Tec

 

Edited July 28, 2020 by NicoN

[N201MKTurbo]

These are not exactly correct, but between the two all of your parts are there.

Century Trim wireing 1.pdf Century Trim wireing 2.pdf

[ArtVandelay]

I have this, I was able to fix problem by just cleaning connections, clearly this wasn’t a factory installation:

[carusoam]

Tom’s pic looks like a relay...

If you have a switch that doesn’t seem to work...

Chase the wires to see where they go... be on the look out for a relay....

relays don’t last forever...

often like to be cleaned...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Missile=Awesome]

13 hours ago, ArtVandelay said:

I have this, I was able to fix problem by just cleaning connections, clearly this wasn’t a factory installation:

Weird, I have that same relay in a Buzz Light Year toy.  Makes wings extend and lights actuate.  To infinity and beyond...