KFC-200 INOP in Flight Only

[John J]

First time Mooney owner and proud 201 owner!...first post on what else my INOP KFC-200 :-)

I have a KFC-200 with KI-256 and Aspen Pro Max. The AP and FD appears to work fine on the ramp - in both pitch and roll the yoke will follow the FD cues. Avionics tech believes torque to be appropriate on yoke. The roll servo motor has been replaced, cleaned, bearings replaced, and likely eliminated as cause. However, in flight the AP will not move the yoke despite the FD showing correct motions both in KI-256 and Aspen. Initially I was focused on roll not following HDG, but it does not seem to follow in pitch either when ALT engaged.

Has anyone seen this situation before or have ideas on cause? Thanks!

[LANCECASPER]

1 hour ago, John J said:

First time Mooney owner and proud 201 owner!...first post on what else my INOP KFC-200 :-)

I have a KFC-200 with KI-256 and Aspen Pro Max. The AP and FD appears to work fine on the ramp - in both pitch and roll the yoke will follow the FD cues. Avionics tech believes torque to be appropriate on yoke. The roll servo motor has been replaced, cleaned, bearings replaced, and likely eliminated as cause. However, in flight the AP will not move the yoke despite the FD showing correct motions both in KI-256 and Aspen. Initially I was focused on roll not following HDG, but it does not seem to follow in pitch either when ALT engaged.

Has anyone seen this situation before or have ideas on cause? Thanks!

Paging @Jake@BevanAviation, the expert on this subject.

[Jake@BevanAviation]

With the A/P engaged and the A/P lever switch in the up position on the KC290 control head, the lateral axis and the pitch axis should have the controls locked in place if you try to move the yoke.  The controls are locked when the solenoids in the servos latch.  The solenoids should latch when the autopilot is engaged.  With a KFC200 system there is a single solenoid engage voltage that is sent out of the computer and paralleled to all the solenoid's.  Do you happen to know if you have the 100 series servos or the 200 series servos?  

Inside the KC295 on the power supply board are two transistors that develop the solenoid engage voltage.  These transistors can fail and there is a very small trace that runs down the edge of the board that can open with high current pull.  I would have the avionics tech look at the system interconnect and verify the engage voltage from the computer.  If the engage voltage is there and the solenoids are latching the next check would be the slip clutch in the servo capstan and the bridle cable tension to the push rod/bell crank.

Edited January 28, 2025 by Jake@BevanAviation

[John J]

I do not know which series of servos I have, but I will ask. Thank you for the insights!