Greg_D

KFC 150 Autopilot Woes

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The autopilot in my 94 Ovation has been giving me trouble lately.  It did fine in the lateral modes but tended to porpoise during climbs and descents with altitudes set in the pre-selector.  Last week I couldn't get the flight director to come up duding the autopilot test.  It's been several years since the KI256 was overhauled, so I thought it might be due again.  After installing the overhauled unit today, I have the same result: an unsuccessful AP test.  I don't get a warning beep that shows a pitch trim failure...in fact, I get no sounds or lights at all after the test button is pushed.  I'm wondering if anyone else here has had a similar failure and what the ultimate fix was.  I spent over $10K on this AP several years ago.  The shop I used basically just replaced/overhauled parts one at a time until they finally replaced the trim switch on the yoke.  That fixed the problem.  I don't want to go down that road again!  Any advice on where to look 1st would be helpful.  Maybe it's time to rip out the King stuff and replace it with Garmin.

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Sounds like the KC 192 computer has a problem. Mid-Continent is probably the best bet to repair B-K components. They are an B-K authorized repair center. Autopilots Central and Executive Autopilots send the units there that they can't repair. Mid-Continent recently repaired my computer - works like new.

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33 minutes ago, PT20J said:

Sounds like the KC 192 computer has a problem. Mid-Continent is probably the best bet to repair B-K components. They are an B-K authorized repair center. Autopilots Central and Executive Autopilots send the units there that they can't repair. Mid-Continent recently repaired my computer - works like new.

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Any idea how much they charge to bench test/diagnose?

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It cost me about $2K. IIRC they charge about $3.5K for an overhaul/exchange. If the repair price gets up to that level I think they cap it there, but best to call them as things may have changed.

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Any idea how many hours on each component?

One thing to consider is what skill is it missing, when does it happen...

The BK autopilot uses a tube to the static system for holding and controlling Altitude change...

The start-up test communicates with all the servos...

Failing the start-up test may be a hint of what to try first... cleaning a lot of connections might be helpful...

The servo That gets the most activity is probably the elevator control... there is a clutch that can get a bit worn and slip causing some funky altitude sinusoids... often initiated in turbulence...

Autopilots Central gets high marks around here...

PP thoughts only, no deep AP experience...

Best regards,

-a-

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I also had a few KFC150 woes before the GFC500 went in. Most times it was a broken wire or pins on the tray connector that have lost their springiness.  The sly hold issues could also be a cold solder that does funky things when the unit heats up.  

Related, I have a working KFC150 setup minus the HSI that I’m going to list for sale soon.  

We all know that the 500 is great kit, but I’ll maintain that some of the biggest un-sexy benefits of going with the 500 is the opportunity for new wiring and intuitive diagnostics on potential failures.  

 

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3 hours ago, 81X said:

...We all know that the 500 is great kit, but I’ll maintain that some of the biggest un-sexy benefits of going with the 500 is the opportunity for new wiring and intuitive diagnostics on potential failures.  

 New wiring, better connectors, digital interconnections, digital fault diagnostic reporting and NO spinning gyros should all help. 

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9 hours ago, PT20J said:

It cost me about $2K. IIRC they charge about $3.5K for an overhaul/exchange. If the repair price gets up to that level I think they cap it there, but best to call them as things may have changed.

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$2K seems crazy expensive just for them to look at it.

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8 hours ago, carusoam said:

Any idea how many hours on each component?

One thing to consider is what skill is it missing, when does it happen...

The BK autopilot uses a tube to the static system for holding and controlling Altitude change...

The start-up test communicates with all the servos...

Failing the start-up test may be a hint of what to try first... cleaning a lot of connections might be helpful...

The servo That gets the most activity is probably the elevator control... there is a clutch that can get a bit worn and slip causing some funky altitude sinusoids... often initiated in turbulence...

Autopilots Central gets high marks around here...

PP thoughts only, no deep AP experience...

Best regards,

-a-

The KI256 was just overhauled.  Everything else has about 250-300 hours on it.  Which connections do you suggest cleaning?  I'm guessing everything in that connect to the AP.

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12 hours ago, Greg_D said:

The autopilot in my 94 Ovation has been giving me trouble lately.  It did fine in the lateral modes but tended to porpoise during climbs and descents with altitudes set in the pre-selector.  Last week I couldn't get the flight director to come up duding the autopilot test.  It's been several years since the KI256 was overhauled, so I thought it might be due again.  After installing the overhauled unit today, I have the same result: an unsuccessful AP test.  I don't get a warning beep that shows a pitch trim failure...in fact, I get no sounds or lights at all after the test button is pushed.  I'm wondering if anyone else here has had a similar failure and what the ultimate fix was.  I spent over $10K on this AP several years ago.  The shop I used basically just replaced/overhauled parts one at a time until they finally replaced the trim switch on the yoke.  That fixed the problem.  I don't want to go down that road again!  Any advice on where to look 1st would be helpful.  Maybe it's time to rip out the King stuff and replace it with Garmin.

If you spend 20-30 minutes on the phone with this guy he will walk you through your KFC150 problems without throwing parts at it. He is the King AP whisperer.

Bob Weber
WebAir Consulting
616 822 1999

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3 hours ago, Greg_D said:

The KI256 was just overhauled.  Everything else has about 250-300 hours on it.  Which connections do you suggest cleaning?  I'm guessing everything in that connect to the AP.

So few hours on everything, it probably isn’t a wear issue...

Mr. Weber and Jake @Bevan Both come with great reviews...

Since the KI256 is an integral part of the AP system, it may be the source of an errant signal...

Being only one person, and only able to follow one path a time...

1) A call to the guys that OH’d and installed the KI256... to see if anything has gone wrong with the last thing that got touched...

2) A call to Bob Weber... because he is an Long time resource for complex BK instruments...

3) A call to Bevan... because they are a great resource for servo OH for BK APs...

90s computers were really good for their time... but without a display, it doesn’t have a way to communicate the failure that it has found...

The beeps that come at the end of the start-up test may tell something... but I have no way to to know what the beeps mean... other than they signal the end of a successful start-up test...

Hope that helps...

PP thoughts only, not an instrument tech...

Best regards,

-a-

 

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5 hours ago, Greg_D said:

$2K seems crazy expensive just for them to look at it.

Sorry, I wasn’t clear. $2k is what it cost to fix it. 

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48 minutes ago, PT20J said:

Sorry, I wasn’t clear. $2k is what it cost to fix it. 

I had same experience with my KFC 150 about a year ago and at about the same cost, except repaired by one of the other authorized repair centers, Duncan aviation. Works rock solid now. It was the main circuit board if I am getting that correctly, and one or two other things. I guess if the auto pilot worked great for 20 years and then needed a grand or two thrown into it, I can’t really complain too much!

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Lots of great advice and apparently many good shops.  My '89 TLS Bravo's autopilot self tested good, but could not hold heading in either HDG ot NAV mode - only alitude.  Took it to Autopilot Central on advice of many. Was in and out in four days.  Right wing roll servo was dead except for responding "ok" on the self test, appeared to have a strange yellowish sludge around it.. They rebuilt it, did complete system checkout, test flight and no issues for the past two years.  Very reasonable cost around $2k.  Completely explained and showed me what they found and what they did.  Would definitely go to them again.

Edited by Cayman44
clarification

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1 hour ago, Cayman44 said:

Lots of great advice and apparently many good shops.  

I think that was true 25 years ago, but I would say that there are a handful of shops that really thoroughly know what they’re doing on the KFC150. Many of the shops will make it worse than it was. My first call, as mentioned in my previous post would be to Bob Weber. He will narrow it down and then refer you to a shop.

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5 hours ago, Greg_D said:

Are the KC192 units dual voltage?  14/28V?

 

I believe it depends on the dash number. 

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I talked to Bob Weber today.  $150 to talk to him, but worth it if his hunch is correct.  He seems to thinks it's the connectors on the mounting rack.  There is a product called Stabilant that can he brushed onto the connectors  that will clean them and enhance the connections.  I'm going to give that a shot and see what happens.

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11 minutes ago, Greg_D said:

I talked to Bob Weber today.  $150 to talk to him, but worth it if his hunch is correct.  He seems to thinks it's the connectors on the mounting rack.  There is a product called Stabilant that can he brushed onto the connectors  that will clean them and enhance the connections.  I'm going to give that a shot and see what happens.

Well, that's certainly worth a try. While you have the unit out, look at the connector in the tray with a flashlight. The individual pins are crimped to the wires and then inserted in the connector shell. A little tang holds them in place and I'm told by my really good avionics tech that sometimes the tang doesn't set right and the pin gets pushed back in the shell where it doesn't make good contact with the computer.

Let us know what you find.

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Greg I looked at the pictures, all the pins look like they are seated properly, the other thing I'm looking for is any of the contacts that don't spring back. I can't see any in the pictures, take a good look as well. Stabilant 22 is great for any connector, I use it on everything I touch.

 

Bob Weber

WebairConsulting.com

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Definitely the computer.  I swapped mine out with another unit and everything worked perfectly.  I guess I’ll be sending mine off next week for a repair estimate.

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Some of the older BK autopilots have a couple of large-ish capacitors in the control box...

Capacitors don’t age very well after a couple of decades... and in BK’s boxes, they sometimes fall out of their mounts...

Based on things I have seen around MS...

Best regards,

-a-

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On 5/17/2019 at 11:33 PM, Greg_D said:

Definitely the computer.  I swapped mine out with another unit and everything worked perfectly.  I guess I’ll be sending mine off next week for a repair estimate.

I recommend Jake at Bevan Aviation. You won't find a sharper or more honest person to deal with.

 

Bob Weber

WebairConsulting.com

616 822 1999

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On 5/18/2019 at 1:33 PM, carusoam said:

Some of the older BK autopilots have a couple of large-ish capacitors in the control box...

Capacitors don’t age very well after a couple of decades... and in BK’s boxes, they sometimes fall out of their mounts...

Based on things I have seen around MS...

Best regards,

-a-

Flux capacitors?

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