Problem with autopilot KFC-150: need help
 

Hi everybody. Maybe somebody can help me out.

I have a PA46 with a autopilot KFC-150 installed. I have a intermittent, occasional problem with the autopilot. After staying for sometimes on the parking, the autopilot fails the startup test: the trim indicator fails and the autopilot disconnects.

After resetting the breakers, the problem persists. I have to fly the plane manually.

This is how it goes:
The avionic specialists from Piper have spent quite some time on fixing this mistake, but no success. The wiring and servos are Ok. The autopilot itself was tested on a stand: no mistakes. The HSI and AI were tested as well.

I appreciate any comments or advice to solve the problem.

This could be a defective trim interrupt/AP disconnect switch. Has the system been tested with the flight-line test set connected so you can measure everything live or have the components been tested individually on the bench?

Thanks for your clue. I believe all system components were tested individually. What is the difference when you test it with the inflight set connected?

What circuit breakers are you pulling. The autopilot CB's or the autopilot and electric trim CB's ? If you are not pulling the electric trim CB's then you should try that as well.

The other thing to do is shut down the engine, turn the master off and on and then try the reset.

I am pulling both the AP and electric trim breakers. Then I have the same problem. After shutting down the engine and resetting the system, I have exactly the same problem.

The computer was tested on the stand. It seems, the a/p computer and the wiring are Ok.

The switch behind the red button on the yoke is a notorious weak point of all these autopilots. We had a similar problem with our Trinidad that worked out to be that issue.

HI
 

Hi, i start to experience the same issue with the KFC-150. They told me was the Trim servo, I changed but still is the same.

Did the Yoke controls fix the issue? (Trim, Red Button)

Thanks

KFC 150
 

Also, have you tried press FD and AP and pull the yoke (in ground), check if the trim rotates, then push the yoke and check trim again.
Mine dosent roll the trim when i pull the Yoke and also i have the AP test fail.

Another problem I have seen with these is the jack socket wiring for the serial connection - typically above your shin/under the panel. The pins can short in the back to each other, joining tx/rx and busying out the unit.