KFC200 - KS271 Servo malfunctioning?

[Lino]

Hello to everybody!

Just joined the forum, I would like to ask the help of somebody.

I purchased recently a Mooney M20K 231.

In the right wing close to the end there is a Roll Servo KS271 with its mount KM275. As soon as I switch the Master switch even with Autopilot disengaged, I hear a noise coming from the servo such as something is permanently rotating inside. As I engage the autopilot it activates the Ailerons otherwise not of course. Autopilot in flight works correctly.

If I take out the autopilot fuse this noise stops.

Is it normal even if the autopilot is disengaged to have this permanent noise (I guess it is a rotation...)? If this is a problem, is it to guess a malfunctioning of the Roll Servo and its electronic inside or of the autopilot?

I thank you very much for your help!

Lino, Austria

[carusoam]

Welcome aboard Lino!

That sounds like you have identified what it is...

But it isn’t normal to have motors rotating continuously in the wings...

What autopilot does your K have? KFC200?

There will be a few recommendations that can be made to help identify what to look for... unfortunately, it is pretty late on the East coast...

You are up early.   

Best regards,

-a-

[Lino]

Hello carusoam, autopilot is a KFC200.....yes I am up early....live in Austria

[PT20J]

This doesn’t make sense.

1 Autopilot works OK

2 Noise happens even with autopilot off but master on.

I’m confused about autopilot fuse remark: it should be a circuit breaker, not a fuse

Does noise stop when you hold AP disconnect on the yoke?

Skip

[carusoam]

Skip,

It may be a translation error... fuse vs. CB...

We can assume, for the moment... the OP meant CB...

 

A Servo running continuously, and attached to a flight control.... sounds a bit scary to me...

+1 for pushing the red disconnect button to determine that the Servo goes quiet...

 

I don’t know enough specifics about the KFC servos to add very much...

It would help to know...

1) Is that the KFC Servo mounted in the wing...?

2) Does it have a clutch that is worn allowing it to stay running...?

 

Who else can we invite to the conversation today? Our bevan Rabel  guy? Our auto pilot guy (Bob Weber)?  And auto pilots central...? My memory isn’t awake yet...

Best regards,

-a-

[Lino]

Hello!

PT20J:

Yes it is a circuit breaker...pulling it out (that of the autopilot) the noise stops (sorry I am not english mothertongue).

As soon as I switch Master on and Radio/Avionic ON I can hear the noise. I did not try to push the red switch on the Yoke as I never engaged the autopilot, can be worth to try but of course if I provide supply why should this reach the servo if the autopilot is disengaged....?)

CARUSOAM:

The servo is mounted on the right wing, type KS271. It is made up of the Roll Servo+Mount, that is KS271+KM275. Yes I guess there is a clutch as otherwise I cannot explain why it makes this noise (guessed rotation) and works correctly because it acts on the alieron actually when autopilot is engaged. However the suspect fact is this guessed rotation even with autopilot disengaged (to me when autopilot is disengaged no power supply should reach the servo.....)

[carusoam]

Should be able to open the wing access panel to have a better look...

My KAP150 is presumed dormant until the avionics master is on, and the AP computer is on...

Its Test sequence needs to be started before anything is supposed to become operational...

The KFC200 is a bit older and less digital...

Sounds like some kind of relay has gotten stuck closed... to allow electricity to get to the motor...

 

One thing I know... there is a company called Bevan-Rabel that OHs BK servos... the company name has been recently updated... to something slightly different...

Something to start looking into... not a recommendation to service the Servo yet...

PP thoughts only, not a mechanic...

Best regards,

-a-

 

[Lino]

Thank you carusoam. I already opened the wing....an avionic engineer working on ultralight but expert enough, suggested me to let the servo been checked (there is electronic inside), pull it out and send to somebody for a check. However this does not convince me because the main issue to me is the energy that should not reach the servo until the AP is activated.

Yes to me also looks somethink more autopilot related rather than servo related...sound of a relay blocked....

[PT20J]

OK, I understand about the circuit breaker. The servo has two components: a motor and a clutch. That's why the manual elevator trim (I know your problem is with the roll servo, but it's the same idea) switch has two halves: one operates the servo and one operates the clutch. You have to press them both to get the trim to work and a test you should do is to make sure that pressing either alone will not run the elevator trim. But back to your issue. I suppose it is possible that some fault runs the motor but not the clutch. That's why I suggested the red A/P disconnect button since it's supposed to interrupt power to the clutch and motor as long as you hold it down. 

Skip

 

[Lino]

OK Thank you carusoam, I will try it as soon as I can reach the airport, within this week probably. Then I will let you know. Thanks again and have a nice week.

Lino

[Bob Weber]

Lino there is a fader circuit that is supposed to inhibit servo drive until the AP is engaged. I can help you here, webairconsulting.com

[PT20J]

@Lino I’d give @Bob Weber a shot. There are precious few folks in the US that really know how to troubleshoot these things anymore - probably a lot fewer in Europe. You can waste a lot of money overhauling and replacing parts trying to find the root cause of a problem. KFC 200 was a great  autopilot - it’s just old.

Skip

[Lino]

Thank you guys! I will contact Bob now!

Best regards, Lino

[DEGWS]

Had  the same problem with my pitch servo. 4 Transistors in the servo have been changed. Servo is working perfect thereafter!

Edited February 4, 2020 by DEGWS

[tmo]

@DEGWS - can you tell us who did the work on your servo?

[DEGWS]

Avionik Straubing in Germany. Best shop in Europe!