KFC150

[KLRDMD]

On my last flight of the day Wednesday I had a trim failure alarm on my KFC150 autopilot. The autopilot had always worked fine before that. The trim light just blinks during the self test and when I push the test switch all the lights illuminate and then the command bars fall out of view and the trim light constantly blinks again. The electric trim still works. I recycled the breaker Wednesday and flew a number of legs today so it has been electrically recycled a number of times now with no improvement. My manual trim wheel seems stiffer than I recall but I rarely use it since I have electric trim, which works fine.

My avionics guy can't get to it for while. Is there somewhere I can lube and see if the manual trim gets easier and maybe the autopilot will work again if something is just binding or dry. If so, I assume removing the belly panel (one piece belly) and looking up in there, something may be obvious ?

Thoughts ?

[Cruiser]

Run the trim wheel all the up and back down with the manual trim wheel between the seats. If it is smooth and does not bind or stick then the airplane side of the autopilot is probably not your problem.

It could be in the computer or it could be a bad servo in the equipment bay. I think the trim servo is in the center with the chain and sprocket. You can try unplugging and cleaning the connector.

Since your electric trim works it would indicate the servo and connections are OK. Problem is probably in the computer.

[KLRDMD]

23 minutes ago, Cruiser said:

Run the trim wheel all the up and back down with the manual trim wheel between the seats. If it is smooth and does not bind or stick then the airplane side of the autopilot is probably not your problem. It could be in the computer or it could be a bad servo in the equipment bay. I think the trim servo is in the center with the chain and sprocket. You can try unplugging and cleaning the connector. Since your electric trim works it would indicate the servo and connections are OK. Problem is probably in the computer.

I have used the manual trim from takeoff to full up and it is fine. I'll run it full down tomorrow. I think my avionics guy said he thinks it is a servo, I think he said there are two. It could be slipping or worn out, I think he said. I'll clean everything tomorrow and see if it is any better.

Thanks -

[donkaye]

1 hour ago, KLRDMD said:

On my last flight of the day Wednesday I had a trim failure alarm on my KFC150 autopilot. The autopilot had always worked fine before that. The trim light just blinks during the self test and when I push the test switch all the lights illuminate and then the command bars fall out of view and the trim light constantly blinks again. The electric trim still works. I recycled the breaker Wednesday and flew a number of legs today so it has been electrically recycled a number of times now with no improvement. My manual trim wheel seems stiffer than I recall but I rarely use it since I have electric trim, which works fine.

My avionics guy can't get to it for while. Is there somewhere I can lube and see if the manual trim gets easier and maybe the autopilot will work again if something is just binding or dry. If so, I assume removing the belly panel (one piece belly) and looking up in there, something may be obvious ?

Thoughts ?

Most likely the AP disconnect switch.   That is the usual culprit.

[KLRDMD]

Just now, donkaye said:

Most likely the AP disconnect switch.   That is the usual culprit.

Why would that lead to a trim alarm indication ?

[donkaye]

Just now, KLRDMD said:

Why would that lead to a trim alarm indication ?

Pushing the Trim Test causes the AP to run a systems check.  If it fails the test by continuing to alarm, the AP won't work.  From experience on 2 occasions over the past 24 years it has been the AP disconnect switch that needed to be replaced.  You could have another problem, but it is unlikely from my experience.

 

 

[KLRDMD]

Just now, donkaye said:

Pushing the Trim Test causes the AP to run a systems check.  If it fails the test by continuing to alarm, the AP won't work.  From experience on 2 occasions over the past 24 years it has been the AP disconnect switch that needed to be replaced.  You could have another problem, but it is unlikely from my experience.

It fails before it gets through the self test. If I force the trim test, it fails that too. I'll look at the switch tomorrow, thanks.

[carusoam]

Ken are you familiar with what each beep means during the start-up test?

BK has the operator's manual on line for the KFC...

Observing which beep is missing can get you closer.

Best regards,

-a-

[KLRDMD]

23 minutes ago, carusoam said:

Ken are you familiar with what each beep means during the start-up test? BK has the operator's manual on line for the KFC...Observing which beep is missing can get you closer.

It isn't beeping at all during the startup test. It really isn't even getting to the startup test, it seems.

[KLRDMD]

I went out to the hangar today and started taking things apart looking for my problem.

First I disassembled the left side of the left yoke, where the A/P disconnect, PTT & electric trim are located. After careful inspection, all seemed well so I put it all back together.

Then I removed the belly panel. Fortunately I have an '85 with the one piece belly. The chain and sprocket  had what looked like carpet contamination so I cleaned that up and lubricated it. There wasn't a lot of debris there but some. Likewise the screw had debris caked in some of the threads on the distal end that required quite a bit of effort to clean. I removed all the old grease with TriFlow, cleaned everything up and re-greased it and now the manual trim moves easier. Those fixes made me feel better about getting it cleaned up and lubed properly but were not the cause of my problem.

Finally I opened up the empennage. I had my son in the cockpit and had him turn on the master and avionics master and it is quite obviously the trim servo that's bad - you can hear it in the cockpit and I felt it when giving power to the unit. I cleaned all the electrical contacts and lubricated the chain and sprocket here too, just because I was there but I need to either get a trim servo or have mine overhauled. It is a KS 179, P/N 065-0052-04, 14V. Any recommendations ?

[LANCECASPER]

These people have an FAA repair Station and repair servo motors. I have not used them, but they posted on here a few years ago.

http://www.bigwoodselectric.com/

[KLRDMD]

Just now, LANCECASPER said:

These people have an FAA repair Station and repair servo motors. I have not used them, but they posted on here a few years ago.

http://www.bigwoodselectric.com/

Thank you

[carusoam]

Nice work defining the issue, Ken.

Best regards,

-a-

[csarles]

I am curious as to the outcome and cost of this. I am having this same servo being rebuilt right now. Insanely expensive. Bendix King is over 6k and 3 weeks.  Duncan in Michigan is 6.5k but only a week. 

[donkaye]

From my experience they should be rebuilt for under 3K.  Try Autopilots Central in Tulsa OK.

[KLRDMD]

8 hours ago, donkaye said:

Try Autopilots Central in Tulsa OK.

My avionics guy said Autopilots Central isn't what it used to be. The guy that owned it sold it to someone else and many of the old time employees have retired. Only the name is the same.

[flyboy0681]

3 hours ago, KLRDMD said:

My avionics guy said Autopilots Central isn't what it used to be. The guy that owned it sold it to someone else and many of the old time employees have retired. Only the name is the same.

Just had my KAP 150 repaired by them and couldn't be happier. They diagnosed the problem and turned it around quickly at a fair price.

[KSMooniac]

Try Bevan-Rabell in Wichita too. Great bench techs.

Sent from my VS985 4G using Tapatalk

[KLRDMD]

25 minutes ago, flyboy0681 said:

Just had my KAP 150 repaired by them and couldn't be happier. They diagnosed the problem and turned it around quickly at a fair price.

Good to know, thanks -

[carqwik]

+1 on Bevan-Rabell.  They fixed a KX-165 and a KI-208 for me in September.  Can't comment on their A/P skills though...but I'd trust them if they say they can!

[KLRDMD]

A bit of an update. This afternoon my avionics shop finally had time to look at the autopilot. It is failing in a way he has never seen in 40 years of doing this (of course). He's calling his guru at Honeywell tomorrow morning but thinks it is the main box itself, not a servo. It fails before it even gets to the self test. I tried to explain that to him last week but he wasn't getting it. After seeing it firsthand today he says he now understands what I was describing 

[kortopates]

On 11/26/2016 at 6:04 PM, LANCECASPER said:

These people have an FAA repair Station and repair servo motors. I have not used them, but they posted on here a few years ago.

http://www.bigwoodselectric.com/

The KFC servos' have become insanely expensive to repair because of the unavailability of the electric servo motor. Bendix King has long since run out of them. Not all servo issues are due to an electric motor though and only if the armature has gone do you really need to have new one built. A couple years ago you were totally out of luck if the issue was the motor. But thank fully we have a few places that can build new servo motors. AP Central now quotes $5K to have their source rebuild the servo motor!

If you send your servo, or any component to BK for repair, their policy requires them to apply every past mod to the unit before they even get to repair. That could be a several mods. Some of those mods are very expensive, some aren't but you don't get choice other than to deny the the repair estimate and go elsewhere.

When you are confronted with a huge repair estimate one of your better options is to find a salvage servo and have a shop yellow tag it for you and also re-set the clutch tension. The problem is that you are looking specifically for a Mooney BK servo, because nobody but BK has the ability and data to legally convert a Beech or Piper BK servo to the Mooney configuration.  And at the age of our BK AP components its very unlikely you'll find a Mooney Servo sitting at salvage yard anymore. I am sure they're gone fast.

[KSMooniac]

The Tru Trak and Trio autopilots cannot get here soon enough!

Sent from my VS985 4G using Tapatalk

[KLRDMD]

Update: The avionics shop diagnosed it as a bad autopilot computer. A yellow tagged one was delivered and installed yesterday and I flew it today. All is well.

[carusoam]

Any idea if it had a bad capacitor? Or anything like that?

Somebody had posted a picture of a capacitor that has migrated out of place.  I can't remember if it was an AP issue or not...

searching for the word capacitor, they seem to be a common electronics challenge in Moonies...

Best regards,

-a-