Electric Trim Quit Working

[Sheriff23]

My electric trim quit working.   I have a 67 M20F with an STEC 60-2 and electric trim. The manual trim works just fine with no issues but the electric is INOP.  It quit working on a recent flight.  The trim switch is the split rocker switch on the pilots yoke.  I was troubleshooting the trim today and when I depress the switch I can hear an actuation or something running in the tail of the airplane, but the trim does not move and the indicator doesn’t change. When I adjust it manually the trim does move and the indicator moves.  
 

I’m planning to have the local Mooney service center look at it but I figured I’d ask here if anyone has any ideas?

[ShuRugal]

My electric trim quit working.   I have a 67 M20F with an STEC 60-2 and electric trim. The manual trim works just fine with no issues but the electric is INOP.  It quit working on a recent flight.  The trim switch is the split rocker switch on the pilots yoke.  I was troubleshooting the trim today and when I depress the switch I can hear an actuation or something running in the tail of the airplane, but the trim does not move and the indicator doesn’t change. When I adjust it manually the trim does move and the indicator moves.  
 
I’m planning to have the local Mooney service center look at it but I figured I’d ask here if anyone has any ideas?

If you hear the trim motor, but trim doesn't move, sounds like a busted chain. Pop the tail access panel off and shine a flashlight in there.

[Cruiser]

you might be hearing the trim motor run. There is a clutch between the motor and the trim gear. 

[Sheriff23]

15 minutes ago, Cruiser said:

you might be hearing the trim motor run. There is a clutch between the motor and the trim gear. 

Doesn’t the split rocker switch activate the trim and the clutch separately?  I’ll check the chain....the MSC is going to look at it. 

[Cruiser]

No, one side of the switch powers the servo, the other side connects to ground. If you hear a clicking sound, that is the servo engaging the clutch. 

[Sheriff23]

On 4/21/2020 at 6:16 PM, Cruiser said:

you might be hearing the trim motor run. There is a clutch between the motor and the trim gear. 

So the MSC checked it...they said the chain is good and one side of the servo is running but it’s not turning the trim gear on the other side. They’re recommending pulling the motor to have the avionics shop bench test it. Has anyone ever heard of that before or are aware of the repair?

[N201MKTurbo]

13 minutes ago, Sheriff23 said:

So the MSC checked it...they said the chain is good and one side of the servo is running but it’s not turning the trim gear on the other side. They’re recommending pulling the motor to have the avionics shop bench test it. Has anyone ever heard of that before or are aware of the repair?

It sounds like the clutch isn’t working. Probably a wiring issue.

[Cruiser]

IF you can find an avionics shop that works on S-Tec , they might have a test unit that plugs into the servo. It will run both the motor in both directions and energize the clutch. 

 

[Sheriff23]

18 minutes ago, N201MKTurbo said:

It sounds like the clutch isn’t working. Probably a wiring issue.

That’s what it was thinking...based on some of the posts on here. Do you suspect the wiring issue is in the yoke at the switch or at the motor?

[N201MKTurbo]

3 minutes ago, Sheriff23 said:

That’s what it was thinking...based on some of the posts on here. Do you suspect the wiring issue is in the yoke at the switch or at the motor?

No way to tell. I would  push the switch to move the trim and start wiggling the wiring until it moves to find the break.

[ShuRugal]

No way to tell.

Multimeter.

[N201MKTurbo]

6 minutes ago, ShuRugal said:

 

 

Multimeter.

 

Sure, you could trace it through, but I bet I can find it a lot faster wiggling wires.

[Sheriff23]

31 minutes ago, N201MKTurbo said:

Sure, you could trace it through, but I bet I can find it a lot faster wiggling wires.

Sounds like I now have plans for Sunday!  Trying to run the trim while wiggling wires....I’d like to avoid having the trim motor pulled if I can. 

[ShuRugal]

Sure, you could trace it through, but I bet I can find it a lot faster wiggling wires.

Assuming it's a broken wire, and not bad contacts in the switch.

[carusoam]

First line of defense...

a spray can of contact cleaner... and cleaning each connecting point from one end to the other...

Switches have a way to collect dirt in them...

PP thoughts only, not an electrician...

Best regards,

-a-

[bgpilot1]

Ah, I owned 9516M for many years.  Great plane.  I believe I had the servos overhauled around 2016.  And I recently had your same issue with my M20K with the KAP150 autopilot, even after the trim servo was overhauled 2x by Duncan Aviation.  The trim motor would operate but the clutch wouldn't engage consistently or at all.  

Call Bob Weber at webairconsulting.com.  He can help you quickly diagnose the issue and work with your avionics/mechanic.  Highly recommend Bob's service.  

Regards,

Barry

Edited July 27, 2020 by bgpilot1

[Sheriff23]

59 minutes ago, bgpilot1 said:

Ah, I owned 9516M for many years.  Great plane.  I believe I had the servos overhauled around 2016.  And I recently had your same issue with my M20K with the KAP150 autopilot, even after the trim servo was overhauled 2x by Duncan Aviation.  The trim motor would operate but the clutch wouldn't engage consistently or at all.  

Call Bob Weber at webairconsulting.com.  He can help you quickly diagnose the issue and work with your avionics/mechanic.  Highly recommend Bob's service.  

Regards,

Barry

Barry,

You’re right....N9516M is a great plane and I love it!  The trim is working great....turned out to be a loose connection on the trim motor wiring harness.

 

sheriff