Jake@BevanAviation

To piggyback on what @LANCECASPER said, I would specifically ask the shop how they aligned the Aspen to the King autopilot and what method did they use. If they mention using the EA100 tool I have seen problems when using that method and I do it a different way. Normally when the alignment is off you might see a slight yoke pump. It's mostly an annoying yoke movement, very minor change in attitude from what I have seen. If it is a larger oscillation around 1-2 hz that could be a tach feedback issue. Typically, when the tach feedback is bad the system is overly aggressive in corrections causing oscillations and noticeable in all modes of flight.

Check the disconnect voltage at the flight computer P2 pin B to aircraft ground. See print for details. KFC 150 M20jk 14-28v.pdf

088-00762-0000 is the part number for the button. Shows active on Honeywell's website but only request for quote. I do not have any stock of this button.

Depending on the dash number for the flight computer it could have the electronic transducer assembly which is known to fail for alt hold functions only.

Good to hear the issue has been resolve and at a decent repair price. If you have any additional issues in the future just let me know.

Century is out of business, getting new parts for the 41 system is practically impossible without support from the manufacture for ribbon cable and other special parts. Unfortunately, any support you find for the system is going to be extremely limited due to part availability. Most common issues with the system was drive transistor failure for the servos, ribbon cables failing, and the transducer failing for alt hold functions. I would try and contact Executive Autopilots and see what support for this system looks like with the manufacture being out of business.

Pretty common failure, the control head needs a new lever switch. The plastic switch gets brittle with age and breaks. Hopefully, you found the little piece of metal that floats between the contacts. Trying to glue the switch back together does not always produce reliable results. The switch contact is designed to float for alignment to the electromagnet. When you glue the contact in place it can no longer self-align to the electromagnet and produces poor latching. The current list from Honeywell is $678.53 for the lever switch. I do have stock and will honor the old price of $241.00 plus labor. However, when I have to order more, I will have to go to the current list from Honeywell. My current lead time is 5-7 business days.

Any time the attitude gyro is repaired or replaced, the system needs to be aligned to the attitude source. This requires the KTS150 test set, you can make an adapter to run the KI256 with the flight computer to be aligned on the bench. The KTS150 comes with harness to align it in the aircraft with the attitude gyro on a tilt stand.

See attached for interconnect. KFC200 M20J-K.pdf

Wrong IM, you need the one for the KAP/KFC 200 system.

Start with checking the S-Tec unit strapping for the compass system, it needs to be strapped for a KCS-55A (KI-525A). If this is not done the system will not work correctly. After that check servo rigging and start-up voltage. Ideally the start-up voltage needs to be under 2VDC, the lower the better. Also, depending on what was removed (DG/HSI) you might want to double check that the unit is still getting the L/R radio error. The GAD29B only provides the Heading/Course error. L/R radio deviation (analog) has to come from the primary navigator to the S-Tec unit.

MET (manual electric trim) has separate circuitry vs autotrim. MET can be functional but have a issue with autotrim functions and still be related to the trim servo. Easiest way to see where the issue is by unplugging the trim servo and monitor the drive lines from the computer for autotrim functions with a DC volt meter. Do a autotrim test (can be push/pull or use the UP/DN switch in the KC290) and monitor the DC volt meter. Ideally without the micro-switches being closed in the pitch servo the computer should generate no drive. When a micro-switch in the pitch servo is closed and remains closed there is a 3-5 second delay before the computer will issue a autotrim command. The autotrim command from the computer will stop when the micro-switch is opened. If the computer checks out with the closing of the pitch servo micro-switches and autotrim drive being issued, the issue is with the trim servo. In normal operation if the computer detects a trim runaway condition (trim feedback) without a autotrim drive command being issued it will issue a trim fail warning. Copies of the IM can be found in the download section for interconnect reference.

It will engage but it will not be happy and will have a constant trim warning.

The logic in the computer for the mode buttons is pretty simple, 5VDC pull up resistors tied to the button switch that pulls the line low when the button is depressed. After that it runs into 8bit shift register IC and then the microprocessor. If I had to guess maybe a issue with the shift register or possibly the microprocessor. I would try and isolate out the KAS297B and see if the issue stops. Also, KC192 computers manufacture between 1991 and 1998 have capacitor leakage problems. There should be a red or black stamp on the side/back of the unit that has a 4 digit code for example 1393 would be the 13th week of 1993. I would try to see if your unit falls in the manufacture range. When the capacitors leak they can cause some really weird issues with the flight computer.

Without the compass valid I believe it will pass pft, but when trying to select a lateral mode it will not allow it. With the heading flag in view it should not allow any lateral modes. If the system is engaged in a lateral control mode and you loose the compass valid the system should disengage. It will allow you to engage with FD and a vertical mode but you will not be able to select a lateral mode.

Record the state of the failure, any flashing lights, what part of the system is INOP. There is a trim fail light in the bezel of the flight computer. During PFT test the trim light will flash 4 times. If the regulated trim voltage is missing you will not get any flashes during PFT and it will have constant flash at the end of the test. KC192 manufactured from 1991-1998 have issues with capacitor leakage and can cause some weird intermittent issues. They tend to fail when they are thermal cycled, they will work when cold but tend to fail when the unit has been running. m20 j kfc 150 interconnect.pdf

If the system will not let you select a lateral mode of operation my guess is you are loosing the compass valid input to the flight computer.

KFC 150 system has a trim monitor circuit that looks at the regulated trim voltage. If for some reason the regulated trim voltage is dropping out or the trim servo is loosing power/ground the regulator will stop functioning. When this happens the system will not pass pft and have a constant flashing trim light. If you could get a video of the failure that might help a little. Weak return springs in the MET (manual electric trim) switch have been known to cause intermittent issues especially the left side of the split rocker.

Nope, you can have a failed transducer board and it will pass PFT.

If the issue is related to alt hold functions only it might be an issue with the transducer board. This board only does alt hold functions. If you can set a climb and descent rate and the aircraft auto-trims properly with power changes I would guess the servos are probably ok. A good test of the auto trim function might not be a bad idea as well. Typically when the transducer boards fail you get a hard up or a hard down when selecting alt hold and they will not level out.

To remove the bezel the unit will have to be removed from the rack and the static line disconnected. There are 4 screws on the side of the unit that hold the bezel to the frame and 4 screws on the inside of the unit that hold the bezel to the motherboard. To remove the 4 screws on the inside you have to take the top cover off and take the screws out of the top motherboard.

@MisfitSELF You could try and swap the lamp with a different one and see if the problem follows the lamp. If the lamp fails to illuminate during PFT the lamp has failed. If the problem doesn't follow the lamp it could be a logic problem with the flight computer.

Servo start-up voltage is super critical on these servos. Ideally it needs to be under 2VDC (the lower the better). Typically, after servicing a unit the start-up is around 800mvDC. If the start-up voltage is too high, the servo is slow to respond causing issues with oscillations or poor tracking. Checking servo start-up voltage is probably a good idea if the servo has not been looked at for some time.

@rocketman if the top and bottom adapter modules match the specific modules needed for the aircraft in theory you should not need to swap. However, it would be nice to know if when the unit was bench check was the aircraft modules installed or were the test modules used? The only servo the system cares about for PFT functions is the trim servo. Specifically, the regulated trim voltage and the feedback from the drive motor. It might be worth it to swap the modules as you have no known history of the ones in the as removed unit. If the modules in the as removed unit had broken pins it could explain why the unit will not PFT. If the shop used the "test modules" there is a good chance the unit worked just fine.

@Fly Boomer Yep, the flight computer needs to have the top and bottom modules installed to start a PFT test. Checked this on the bench with a test KC191 (KAP-150). Without the modules the unit will not PFT. Only the trim annunciation stays lit.