Jake@BevanAviation

@steve wilbur If MET (manual electric trim) has stopped functioning it could be wiring issues but most commonly it is a issue with the trim voltage regulator inside the trim servo. The KC192 actively monitors this regulated voltage and if it is out of mfg specs it will cause a PFT failure. If there is no regulated voltage the KC192 will have no flashing trim annunciations during the pft, you will get a flashing trim fail at the end of the test and it will not allow the system to work. Best place to start is to see if the voltage regulator is working in the trim servo. At the trim servo pin A sends out the regulated voltage to the yoke switch, there is a parallel to the computer for the voltage monitor on P2 pin W. See prints for details. If the trim servo has a good power source and a good ground it should regulate a voltage. Depending on the dash number of the unit the regulated voltage for a 14V systems is 12+/-1VDC and for a 28V systems 26+/-1VDC. If you are handy with a voltage meter check power and ground at the trim servo connector, if that looks good check the regulated voltage with the trim servo plugged in via backing pinning the trim servo connector, at the MET switch on the yoke, or at the computer connector. KFC 150 M20jk 14-28v.pdf

@DonMuncy Sounds like you are having some issues with the snap domes. This issue can be resolved by removing the motherboard assembly, removing the old snap domes, cleaning the contacts, and replacing the domes with new ones. If you would like a rough estimate on repair cost give us a call and ask for Mike. He should be able to provide lead time and a repair estimate for you. 316-946-4870

Make sure the STEC 40 is configured for the correct compass system per the install for the Aspen. It should be a KCS-55A (KI-525A). There should be a placard on the system 40 that says what compass system it is configured for. If the old compass system was not a KCS-55A the unit will have to be modified per the STEC drawing.

The KAP/KFC150 system would not be happy if trim power was removed but if it is interrupting the regulated voltage from the trim servo after the parallel to the computer it should continue to work. However, this would not conform to the install manual . More information about the system in the aircraft is needed to determine if it is operating correctly.

@bcbender10 Sounds like the voltage regulator in the trim servo has failed. When this happens you will have no MET (manual electric trim) and the flight computer will not pass PFT. I would suggest doing the normal power and ground checks on the servo connector and if that checks good have the trim servo bench checked. Also, if you get no flashes of the trim annunciation during PFT that is a good indication the voltage regulator has failed. During PFT there should be 4 flashes of the trim annunciation if the systems passes you should get a flashing AP light for approximately 12-13 times. Anything else would indicate some kind of failure detected. One last thing, if the flight computer was manufactured within 1993-1998 those units are known to have capacitor leakage issues that will cause some weird issues. The -15 units can only be serviced at certain shops (Mid-Continent, Duncan, Honeywell) the older -2 (14V) and -3 (28V) units can be serviced in the field if the shops have the necessary equipment and MM documentation. KFC 150 M20jk 14-28v.pdf

@DCarlton 088-00866-0001 should be the part number for the knob. I am sure you can find some online cheaper than a new one from Honeywell.

@tim417 If you would like to give us a call and ask for Mike or Bill. They should be able to give you a rough idea on possible repair cost or maybe a exchange as we do have some used units available. 316-946-4870 Thanks

@Scottknoll If it was wired correctly it should not engage with the amber cats eye illuminated, indicating a EA100 failure. If the EA100 goes down in flight and it is the source of the attitude information to the KFC150 with no disconnect you will have a very interesting ride. See print for details. Aspen EA100 to KFC150.pdf

@spayne59 A 1hz oscillation can also be a product of a bad tach generator inside the pitch servo. Without a negative feedback from the tach generator the servo will run at full speed all the time. This ends up causing over corrections that lead into a constant oscillation. It is also possible if the gyro alignment procedure was not done that is outlined in the Garmin IM it could cause issues. If the pitch gain is incorrect it can cause the A/P system to react to pitch changes incorrectly. Ask your shop if they did the gyro alignment procedure outlined in the Garmin IM (5.7.2.2). If this has not been done, it must be done before anything else is looked at. If they have access to the KTS158 flight line test set the process is very simple. If they don't they will need to build a harness per the IM. That is where I would start.

@Richard Allen .6 DC drive voltage at the servo connector is way low. My guess is something failed on the pitch board possibly drive transistors.

@Htmlkid My guess would be the TC valid to the system 50 is dropping out causing the system to disconnect. It sounds like the valid flag is what you are seeing in the indicator come into view. I would call Mid Continent (316-630-0101) and ask for Doug in the gyro shop. Tell him what you are seeing and see what his suggestion is.

If you have tested the motor and it works my guess is something went wrong with the drive transistors on the pitch board assembly. I would check the pitch servo connector using the up/down buttons and see if you get any DC drive voltage at the servo connector.

Depends on the failure of the unit. I am currently waiting on boards from Century to fix a C2000 that is already here. Century said lead time was 4-6 weeks for board assemblies. There is a capacitor that likes to short that will cause a pico fuse to open and render the unit INOP. If you have a better description of the failure that might give me a idea of what the problem could be.

For a ground check as long as the model number and voltage are the same you should be fine.

@Greg_D See image for connector pin-out. If you were going to swap computers you would have to make sure the part numbers were the same, the same voltage, and the same adapter chips if you were going to try and fly on it.

If the FD bars respond to heading bug changes with HDG mode selected my guess is roll servo problem possibly bad motor or transistors. If you are handy with a voltage meter you can check the drive voltage from the computer at the roll servo connector pins D and L. With the computer on, a level attitude gyro, and hdg mode selected moving the bug should create a positive or negative DC drive voltage (left or right of lubber line) if the meter is across pins D and L. Under the lubber the voltage should be close to 0VDC. This would break it down to bad computer if you get no voltage or bad servo if you get the drive voltage at the meter.

You might give us a call and ask for Mike or Bill, they should be able to give a rough estimate on what you would be looking at for a repair. Biggest problem with the KX155-165 units tends to be display issues and cap leakage.

I have seen a 55x fail on auto-trim and be thermal related. When the unit was cold everything worked, add a little heat and it would stop driving in one direction. Sent the unit back to S-Tec and they replaced the board assembly.

@Pierre07Sounds like the alt hold board has some issues, possible transducer failure. Normally when they fail they drive hard up or hard down but always the same direction, fast and aggressive. There is a slight possibility the static line to the transducer could be plugged. You can unhook the line and try selecting alt hold on the ground with the gyro close to level and FD mode active. If the bars drop rapidly my guess is there is a fault in the flight computer. If you can use the vertical modifier in the control head to set a climb or descent and the aircraft maintains that attitude most of the system is working. If using CWS to establish level flight with everything in trim and then you add in ALT hold the FD bars deviate and the computer chases, everything points to the alt hold board.

@FloridaMan Bulbs are 14 or 28V. King part numbers are 037-00032-0008 (14V) 037-00032-0010 (28V).

@carusoam Alt hold is accomplished by multiple components working together as a system. Pitch servo, trim servo, Flight computer and attitude gyro. If one component has issues the system will struggle at maintaining alt hold. For example if the slip clutch for the trim servo is weak it will struggle to trim the aircraft in flight, it might work fine on the ground but with the added load in flight it will slip early and not properly adjust the trim. Slip clutches do wear, they are composed of spring washers, friction plates and carbon disks. With use the carbon disk will glaze the surface of the friction plate and slippage can occur. Most commonly when there is a excessive use of spray lubricant and it works its way into the assembly it will contaminate the disk and it will slip. Depending on the servo series 100 vs 200 the slip clutch assembly will be part of the servo (100) or part of the servo mount (200). Other things like high servo start-up voltage, broken trim springs, and faulty micro switch in the pitch servo will cause problems as well. If the OP knows they have a issue with auto trim I would start with doing a good ground test of the auto trim system. Depending on the outcome of the test that should lead them in the direction of the problem. One thing that has got me in the past with Mooney is if the trim servo is struggling to trim on the ground it will be worse in flight, things like added resistance to the trim system can cause oscillations in flight. Also, if there is a issue with the attitude gyro like stiff bearings causing slow rotor speed it will cause issues as well. Sometimes you can induce a vibration to the gyro in flight and if it starts to oscillate the AI might need to be looked at . Something to always look for on a mechanical AI is when the gyro starts to spin up is does the attitude card shake out or is it slow to erect? If it is slow to erect that is a sign the bearings are getting stiff.

So for science I hooked up a KC295 and trim servo to my bench tester and if you hold CWS and use MET it will run the trim servo and not disconnect. I even went and tried in in a 58P that is in the hangar. Personally I have never tried this in flight cause I know that you cant have both at the same time (auto trim and MET). In a normal operation without CWS being used you will get the system to disconnect 100% when using MET with the AP on.

CWS is used to release the solenoids so the pilot can control the aircraft as long as the switch is held. When released the system will sync to the current pitch attitude but the roll axis will try to follow the heading bug or course pointer if the individual mode is selected and the bug/pointer is not under the lubber line. You can not have autotrim and MET (manual electric trim) at the same time. If the computer is engaged and you move the left side of the spilt rocker it will disconnect the system. Things that will keep a KFC 200 from engaging are listed below failure of the power supply triggering the power monitor circuit left side of the split rocker not returning to a neutral position open current path for the holding coil in the control head compass valid missing when selecting a lateral control mode failure of autopilot disconnect relay broken engage lever switch The key to quickly breaking down the system is does the engage switch latch? If so do the solenoids engage? Do you get the AP on annunciation in the remote annunciator? If the switch does not latch can you hold it closed and the system try to respond to input changes?

@philip_gWith a Century 41 if you have a flashing NAV, APPR or GS annunciation it typically means the computer is not seeing a valid signal for navigation and will continue to flash the associated mode till the signal is valid. Depending on what mode of operation you are wanting, the computer should be getting a lateral flag valid for lateral tacking and a vertical flag valid for vertical guidance. These connections should be depicted in the IM for the associated Garmin interconnect. The valid information should come out of the GDU to the C41 computer.

I apologize, I referenced the wrong system in my initial reply to the OP. The KFC 150 still uses LBT but the circuit is vastly different from the KFC 200 system. The KFC 150 uses microprocessors, digital converters and multiplexers to generate a composite roll command signal. This composite signal is what is used to drive the servo amplifiers. There is a nav deviation null pot inside the computer used to adjust a offsite nav signal before it goes to the multiplexer and summed with the course error. There are two additional pots located on the front face of the unit labeled RN and RC. RN for roll null, used to null the AI roll error, RC is roll centering that can be adjusted for track discrepancies . A word of caution, be very careful when adjusting the RN or RC pots as you can damage the pot. Use a long small flat blade jewelers screwdriver to adjust the pot. Make small adjustments and wait for the computer to settle before adjusting again.