brianucsf Posted April 27 Report Share Posted April 27 I purchased a 1980 M20J six months ago with a KFC200 controlled by an Aspen EFD1000 via an EA100. Twice over that time I had the autopilot fail to engage (switch wouldn't stay up and AP light blinked) but after a few minutes of hand flying if I tried again it would behave properly. A few flights ago, however, the autopilot wouldn't engage and hasn't done so since then. If I push and hold the test button when on the ground, all lights go on except the trim light never turns on nor do I hear a tone. However, I hadn't ever used the test button before (I just ground tested by moving the heading bug and pitch rocker) so I wasn't sure what to expect on my unit. After reading about the potential flaky switch latch mechanism, I tried a ground test by holding the switch in the on position and moving the heading bug - the yoke moved in the expected direction so I thought perhaps a faulty switch was the problem. While flying, I held the switch in the on position with a rubber band and it flew like it was on rails for at least 10-20 minutes with both GPSS heading and altitude locked in. Suddenly, however, it started making a left bank (when the FD display was showing straight and level). I shut it off and tried one more time in heading mode (holding the switch in the on position since it wouldn't latch there), but it continued to want to bank left even when the heading bug was directing a right turn or level flight. Any thoughts on what the problem may be? I'm handy enough with troubleshooting and a multimeter, but I'm by no means an A&P or avionics guy. Is there additional troubleshooting I could do to help narrow down the issue? One final note, which I think is unrelated, is that occasionally two hours or so into flights the EA100 system will glitch, I will receive an aural alert to "Check EFIS", and the autopilot will kick off. Thanks to the wisdom of MooneySpace, I now know to pop the EA100 breaker, wait a few seconds, reset it, and a minute or so later everything would work like a charm. This seems like a completely different issue (which I can manage with the circuit breaker trick) but wanted to mention it in case it was important. Thanks in advance for any assistance. Quote Link to comment Share on other sites More sharing options...
GMBrown Posted April 27 Report Share Posted April 27 For your KFC 200 nightmare to end, contact Bevan. (Jake@BevanAviation) 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 27 Report Share Posted April 27 Nice problem statement Brian! sounds like something needs to be cleaned… there are so many independent parts to the system that are all interrelated… @Jake@BevanAviation Jake is a good guy for this… always use the test function of the AP…. It tests all the things better than we can from the left seat … One thing the older BK APs have in common… aging capacitors… and servo motors… and, if you forget to turn the electric trim system on… good luck with your next steps… PP thoughts only, not an avionics guru… Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
anthonydesmet Posted April 27 Report Share Posted April 27 I have same configuration and I’ve had that happen before. Mine was related to the plug in the back of the Aspen due to lose connection. My connector would back out of the Aspen….connector side springs were old and warn. before you fly next time get under the panel, reach up and push that connector in. You might not feel it move much but if it’s off a little some pins might not be making contact. Quote Link to comment Share on other sites More sharing options...
PeteMc Posted April 27 Report Share Posted April 27 I'm with @carusoam... Go into your avionics shop and have them clean and reset all the cards and see if that resolves the issue. If not, then I guess you need to talk to them about finding out what the issue is. 1 Quote Link to comment Share on other sites More sharing options...
LANCECASPER Posted April 27 Report Share Posted April 27 I had an Ovation with two Aspens and a KFC225 autopilot. One thing that I learned that I had to do was make sure the Aspen AHRS was up and I had a valid horizon on the PFD before powering the autopilot. Otherwise it would fail the test every time. I added that to my checklist and was good to go. If that doesn't do it, @Jake@BevanAviation is your go-to guy. 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 27 Report Share Posted April 27 Also keep in mind… how ancient and limited the computing power of the KFC is… Think IBM XT desk top as a superior computer… fresh from the 1980s… it will do basic things well… But it doesn’t have much capacity for error checking beyond the start up phase… the order of turning things on, and timing of the steps, can be important… and there is no feed back of what it found wrong… no color screen to give any advice… Think 1980s while doing the trouble shooting. And when you find out what steps work… be sure to write them down… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Jake@BevanAviation Posted April 28 Report Share Posted April 28 @brianucsf With the Aspen PFD and the EA100 if the PFD gets a red X on the display, the EA100 will cause the flight computer to disengage. The EA100 is interconnected with the flight computer in a manner that it will not allow you to engage the system with a invalid attitude signal. Typically, you will get a amber fail annunciation from the annunciator tied to the EA100 somewhere in the panel. Normally they are within pilots view of the PFD. Refer to the Aspen IM for details. The Aspen ACU provides the flight computer with input errors like heading, course, left/right deviation, up/down deviation, GPSS, ect. If something fails in the ACU the flight computer will follow the failure. For example, if the heading output from the ACU was to fail and get stuck at a constant voltage the computer will not respond to heading bug changes correctly. ACU failures can happen just not frequent. All King servos can have motor, tach generator or drive transistors issues at some point. Typically when the drive transistors fail you will only get drive in one direction, or constant drive one direction. One thing I always ask is how are the FD bars responding to input changes. If the FD bars respond correctly to input error changes that checks about 95% of the drive circuitry inside the flight computer. There is one op amp stage left in the flight computer the generates the servo command voltage. This op amp can fail but a simple voltage check at the servo connector will tell us if the computer is the problem or the servo. The control head a/p engage lever is know to have issues and is a pretty common failure. Inside the unit the lever switch holds a small piece of metal. When you engage the system there is a coil inside that will become a electromagnet when voltage is passed. If the plastic tabs break on the lever that holds the metal piece there is nothing for the electromagnet to grab and the switch will not latch. The coil can fail but it is much more common for the plastic tabs to break. There are several other things that can cause issues and after reading your post it sounds like you have a couple of issues. If you would like to give me a call Monday I can tell you what I would look for. Quote Link to comment Share on other sites More sharing options...
brianucsf Posted April 28 Author Report Share Posted April 28 Thanks for all the helpful feedback. I will try to reseat the connections later this week and then proceed from there. Quote Link to comment Share on other sites More sharing options...
brianucsf Posted May 27 Author Report Share Posted May 27 I finally got a chance to dig into this a bit further today. I did some troubleshooting suggested by Jake and found: 1) The harness from the computer out at the roll servo is sending out expected readings across the D and L pins. When the autopilot is held on and heading bug is turned in one direction the voltage is positive, in the other negative, and when my 11 year old son centered the heading bug as well as he could, it ended up close to zero. ALso, the FD bars on the Aspen showed the expected banks. From all that I assume that the computer is working well, and the problem is the roll servo. 2) I cleaned the contacts on the main connector between the servo and the computer, to no avail. The ground from the servo looked a bit suspect, so I cleaned that as well, and again, it didn't fix the issue. 3) When the radio master is turned on (but not the autopilot) there is a whirring noise from the servo but the cable doesn't turn. It sounded like a fan, but I don't know if there is a fan in that unit. 4) In the past, when holding the autopilot in the up on position, it would show the FD correctly for the heading bug location, but would actually pull the ailerons full left. Once I cleaned and reassembled, the servo would move perhaps 1/8 turn and seem to sort of stall. Once it stalled, even if I had my son rotate the heading bug, it didn't really move. 5) I'm not sure if I have a KS178 or KS201 roll servo. I tried to remove the two bolts closest to the access panel, but the servo unit didn't want to come out after that. I was afraid I would somehow mess up the aileron control, so I didn't keep experimenting. I've attached a few pictures showing the bracket. So my questions are: 1) Do you agree that it sounds like the roll servo needs to be removed and serviced/replaced? 2) Do you know of a instruction manual explaining how to remove whichever roll servo I have (or, is it tricky enough that it is best left to the professionals)? Thanks so much for your advice. Brian Quote Link to comment Share on other sites More sharing options...
LANCECASPER Posted May 27 Report Share Posted May 27 20 hours ago, brianucsf said: I finally got a chance to dig into this a bit further today. I did some troubleshooting suggested by Jake and found: 1) The harness from the computer out at the roll servo is sending out expected readings across the D and L pins. When the autopilot is held on and heading bug is turned in one direction the voltage is positive, in the other negative, and when my 11 year old son centered the heading bug as well as he could, it ended up close to zero. ALso, the FD bars on the Aspen showed the expected banks. From all that I assume that the computer is working well, and the problem is the roll servo. 2) I cleaned the contacts on the main connector between the servo and the computer, to no avail. The ground from the servo looked a bit suspect, so I cleaned that as well, and again, it didn't fix the issue. 3) When the radio master is turned on (but not the autopilot) there is a whirring noise from the servo but the cable doesn't turn. It sounded like a fan, but I don't know if there is a fan in that unit. 4) In the past, when holding the autopilot in the up on position, it would show the FD correctly for the heading bug location, but would actually pull the ailerons full left. Once I cleaned and reassembled, the servo would move perhaps 1/8 turn and seem to sort of stall. Once it stalled, even if I had my son rotate the heading bug, it didn't really move. 5) I'm not sure if I have a KS178 or KS201 roll servo. I tried to remove the two bolts closest to the access panel, but the servo unit didn't want to come out after that. I was afraid I would somehow mess up the aileron control, so I didn't keep experimenting. I've attached a few pictures showing the bracket. So my questions are: 1) Do you agree that it sounds like the roll servo needs to be removed and serviced/replaced? 2) Do you know of a instruction manual explaining how to remove whichever roll servo I have (or, is it tricky enough that it is best left to the professionals)? Thanks so much for your advice. Brian I wouldn’t let just any IA do it. I would let someone who works on autopilots do it. I definitely wouldn’t do it myself. Quote Link to comment Share on other sites More sharing options...
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