KAP140 Autopilot Pitch Fault

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creativewebz
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Re: KAP140 Autopilot Pitch Fault

Post by creativewebz »

Rich wrote:Grant, if you can move the trim wheel (independent of the A/P trim) and the trim tab doesn't move you've got a problem with your trim control linkage. A gunked-up damper rod alone makes the trim inordinately stiff.

(BTW, I looked up N414DS and the FAA shows it as the registered number for a Cessna 414 owned by someone in Clackamas, OR. - you might want to look into that.)
Rich, I just went to the FAA n-number look up tool and it showes my proper name and address here in New Orleans. Can you PM me the link you are looking at?
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Re: KAP140 Autopilot Pitch Fault

Post by creativewebz »

I apologize sir, I see what you were talking about now. I had the wrong number on my profile. Thanks!!!!
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Re: KAP140 Autopilot Pitch Fault

Post by 40flyer »

I may have a different situation than those listed above. Today after transitioning to slow flight while at level altitude and then resuming cruise speed I got a recurring "Check pitch trim" aural alert and a "Trim Fail" msg on the PFD. The aural alert was persistent even after cycling the A/P circuit breaker. Both the manual trim and electric trim seemed to work fine, in both directions, even when I checked back on ground after restarting the airplane after refueling. I cannot resolve the trim fail and aural alert every 3 seconds. A/P seems to work fine otherwise. Anyone know how to clear the fault??
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Re: KAP140 Autopilot Pitch Fault

Post by 40flyer »

Just an update on the previous post. Pressing the A/P disconnect switch clears the fault and the aural alert but they return after about 7-8 seconds. If it’s a switch failure it’s not clear how to remove and check the MET and A/P switches. The MET switch has 2 screws which I can remove but the switch does not come out when pulled.
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Re: KAP140 Autopilot Pitch Fault

Post by blsewardjr »

Knock on wood, we seemed to have fixed my KAP140 issue. Autopilot was refusing to go beyond PFT 3, P and R were illuminating, and electric trim had stopped working. Problem was intermediate but getting worse. Turned out to be a loose connection in the main power connection for the autopilot under the pilot's seat. Basically, the servos were not getting power. Took over an hour to get the seats back in. Tempted to do the mod to put in a hatch but several thousand dollars.
Bernie Seward, IR, AGI
2003 DA40 N377DS
KCHO Charlottesville, VA
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Re: KAP140 Autopilot Pitch Fault

Post by Steve »

Bernie:

That's great. Can you be more specific about which connector? The autopilot main power in my airplane goes directly to the KC-140 box from the Autopilot CB. I see on the schematic a large connector with about 50 pins (P2406/J2406) but don't recall seeing it under the seats.

Mine is still not working. It is not the KC-140 box, since I swapped it for a known good one last week and got the same fault. I am taking the seats out next week to R&R my KG-102A DG for overhaul. I plan to do more diagnostic work on the AP system then. I was planning to manually exercise the servo clutches and servos (via my laptop through the diagnostic port). I will have to find that big connector also. Hopefully, this will further localize the problem, but any more specific information you could provide would be appreciated.

Steve
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Re: KAP140 Autopilot Pitch Fault

Post by blsewardjr »

Steve- The one we tightened was a large, I think black, cylindrical connector that either screws together or is held together by a donut nut that you tighten. Mine was loose, probably from when the seats were removed to be re-furbished recently or from my annual which followed that immediately. If you follow the wires from the control stick it should be up near the forward bulkhead on the inboard side of the area under the pilot's seat.

Because the electric pitch trim wasn't working, we first checked the pitch trim servo, which is located under the co-pilot seat, but it was getting power. (It has a metallic connector on the floor.) Then we tested the autopilot disconnect on co-pilot side, which flows through a small white connector near the stick, but it was working. We also pulled the KC-140 box and re-seated it but that didn't change anything. Finally, we did some more thinking and decided to zero in on the connector on the pilot side because of the fact that the KC-140 box was indicating that we were having a pitch AND roll issue -- both the P and the R were illuminated. Unlike the co-pilot side, the pilot side has numerous wires flowing from the stick and elsewhere that go through the large cylindrical connector. According to my avionics guy, it was the connector where the power? commands? to all of the servos flows.

I hope this is helpful. If you'd like me to seek clarification from my avionics guy, I'm happy to do so. Bernie
Bernie Seward, IR, AGI
2003 DA40 N377DS
KCHO Charlottesville, VA
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Re: KAP140 Autopilot Pitch Fault

Post by Steve »

Bernie:

Thanks, that is helpful information. I will look for that connector and start there.

Steve
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Re: KAP140 Autopilot Pitch Fault

Post by Steve »

So, today was "work-on-the-autopilot" day (along with pull the DG out so I can send it for overhaul). After the fun part of removing the seats, i went looking for the large connector that Bernie mentioned was the problem in his airplane. Well, mine doesn't have one (in the location specified). In my airplane, that connector is way in the back of the instrument panel, behind the radio stack:
DSCN5027.jpg
Mine seemed tightly attached (no one has ever been back there, as far as I know). I was able to eventually disconnect it and spray some contact cleaner in there. No joy after reconnecting - same error on autopilot PFT test. So, I connected my laptop to the service jack under the panel, and started going through the menus. I noticed that the Discrete Inputs list was showing the Autopilot disconnect switch as "Yes", even though I wasn't pushing one of them. I was able to make enough slack in the control stick wiring harnesses to push the switches out. Turns out that they are NC switches, and that the Pilot's side was open! I used a clip lead to short it:
DSCN5028.jpg
The autopilot went through its PFT correctly! Luckily the other section of the DPDT pushbutton was good, so I just moved the wires over to that section:
DSCN5030.jpg
Sao, it turned out to be the simplest thing - a bad switch.

Steve
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Re: KAP140 Autopilot Pitch Fault

Post by blsewardjr »

So, I spoke too quickly. After several successful flight the autopilot failed to come on again, although it did so after I pulled the circuit breaker and waited approximately 10 minutes. Therefore, we opened up the pilot's side seat again and did some serious testing of the coupling that had been loose. We cleaned all nine prongs and receptors, some of which were tarnished and made sure no wires were crimped. Tested it five times with no failures and then put the seat back in. We'll see how it goes. This time I took a couple of pictures of the coupling, which is connected to the pilot's stick.
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Bernie Seward, IR, AGI
2003 DA40 N377DS
KCHO Charlottesville, VA
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