KAP 150 problem solved

[PT20J]

It started with the autopilot failing in flight at random intervals. It would annunciate a TRIM failure and kick off. Sometimes, it would also trip the TRIM breaker/switch. Then eventually, it would intermittently fail TEST.  I sent the KC 191 computer to Autopilots Central and they eventually sent it to Mid-Continent. The problem turned out to be a cold solder joint on the connector for the internal cable that connects the two circuit boards together.

When I got it back, the autopilot worked except HDG and NAV moves were inop. I checked some voltages on the KC 191 tray connector and determined that the outputs from the Aspen ACU were bad. I swapped the ACU for one I bought on eBay and now all is good.

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[LANCECASPER]

1 hour ago, PT20J said:

It started with the autopilot failing in flight at random intervals. It would annunciate a TRIM failure and kick off. Sometimes, it would also trip the TRIM breaker/switch. Then eventually, it would intermittently fail TEST.  I sent the KC 191 computer to Autopilots Central and they eventually sent it to Mid-Continent. The problem turned out to be a cold solder joint on the connector for the internal cable that connects the two circuit boards together.

When I got it back, the autopilot worked except HDG and NAV moves were inop. I checked some voltages on the KC 191 tray connector and determined that the outputs from the Aspen ACU were bad. I swapped the ACU for one I bought on eBay and now all is good.

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Would you mind sharing what the cost was for the KC 191 repair? My KFC150 is of the same vintage (1993) as yours (1994) and although I haven't had that problem yet, I'm sure it's only a matter of time.

[PT20J]

Autopilots Central charged me $2119.78 for the KC 191 repair. They couldn't initially reproduce the problem, but found a voltage low and suspected the power supply. They replaced a bunch of electrolytic capacitors and a couple of resistors in the power supply as the capacitors are known to leak electrolyte when they get old. I'm sure this improved the long-term reliability of the computer, but it didn't fix the problem. They took it back and ran it on the bench for a month and did see the problem off an on, but could not determine the cause. At that point, they sent it to Mid-Continent and there the problem was found and fixed.  Autopilots Central handled all this additional work under warranty so I only paid the initial $2K.

If I had another autopilot problem that required taking the airplane to the shop, I would not hesitate to go to Autopilots Central or Executive Autopilots. But, I think Mid-Continent might be the better choice for repair of individual components. M-C is a BendixKing repair station and Autopilots Central and Executive Autopilots go to them when they can't solve a problem or get parts.

I talked to Aspen about the ACU and got the impression that failures are not that uncommon. It seems just a coincidence that the ACU failed while I was fiddling with the autopilot. In my case, it is probably a bad 15V internal reference since the problem affected both the CRS and HDG outputs. Good news is that I found a good used ACU for $550 on eBay and Aspen will exchange one for $660 or sell a new one for $880 (list prices, maybe some negotiating room if you do a lot of business with an Aspen dealer) so they aren't expensive as airplane parts go. This is the original ACU, not the ACU2.

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[PT20J]

Went out to test the autopilot today. Wilder ride than I had planned. Moderate turbulence ( hit my head on the ceiling a couple of times despite having the belts really cinched down, had trouble tuning radios, difficult to read the approach plate - yeah, it was rough). A/P captured KPAE 16R Y ILS localizer and glideslope perfectly. Wind picked up with ATIS advertising 160 at 20 gusting to 32. (Well, at least it’s straight down the runway). Big power changes up and down to maintain 90 kts approach speed. KAP 150 never off more than half a dot localizer or glideslope to DA. It may be old, but it’s a pretty darn good autopilot. Landing surprisingly uneventful. Bonanza following me in called it “sporty.”