KFC-150 question

[Glen Davis]

I have a Bendix king KFC - 150 auto pilot in my 1984 J.  I purchased a used HSI or what King calls a PNI (Pictoral navigation indicator). I believe the model is a KI525. My aircraft is 12 volt. I’m not sure if the used unit I purchased is 12 V or 24 V. I have enclosed a picture of the unit showing the front as well as the tag on the back. Can someone tell me if this is a 12 V unit which I can just swap out for mine or is it a 24 V unit. Both 12 and 24 volts are indicated on the tag on the back of the unit.

[Rwsavory]

Pretty sure it does both voltages. The remote gyro has a switch to select between the two.

[LANCECASPER]

They are dual voltage, but make sure it is the same part number as the one you are replacing. Over the years these have had different options on them, hence different part numbers, such as bootstrapping, which would provide a heading to another device, such as a Stormscope as an example. (Example: https://www.bennettavionics.com/ki-525a-hsi-indicator/)

What makes you think that it's the KI-525? Most of the time it's the KG-102A remote gyro that needs attention. 

[jaylw314]

Search for it by part number, AFAIK you have to replace it with the same version.  The -01 has the bootstrap function.

I hadn't noticed before, but those voltage/current numbers seem to be just for the lighting  

Edited January 3, 2023 by jaylw314

[Glen Davis]

3 hours ago, LANCECASPER said:

They are dual voltage, but make sure it is the same part number as the one you are replacing. Over the years these have had different options on them, hence different part numbers, such as bootstrapping, which would provide a heading to another device, such as a Stormscope as an example. (Example: https://www.bennettavionics.com/ki-525a-hsi-indicator/)

What makes you think that it's the KI-525? Most of the time it's the KG-102A remote gyro that needs attention. 

The problem is when I engage the AP in the heading mode, shrlty after takeoff, the aircraft hunts left and right for about 5 minutes, then stops hunting.  From that point on it works perfectlty.  It's always and only when first engaged.  When I posted this problem to the group the largest majority of answers to what they thought the problem would be was the indicator. Therefore I found a replacement indicator to try before I went the more expensive route I bringing it to a shop.  Even on the ground, when I engage the AP, it hunts right and left.  After a few minutes it stops hunting.

[PT20J]

2 hours ago, Glen Davis said:

The problem is when I engage the AP in the heading mode, shrlty after takeoff, the aircraft hunts left and right for about 5 minutes, then stops hunting.  From that point on it works perfectlty.  It's always and only when first engaged.  When I posted this problem to the group the largest majority of answers to what they thought the problem would be was the indicator. Therefore I found a replacement indicator to try before I went the more expensive route I bringing it to a shop.  Even on the ground, when I engage the AP, it hunts right and left.  After a few minutes it stops hunting.

@Jake@BevanAviation would know. 

[Jake@BevanAviation]

If in just attitude mode, with heading not selected and the system has the roll oscillation, with a level ADI. My first thought is tach gen feedback from the roll servo.  If the compass system has not finished slaving the card will oscillate back and forth until it is slaved.  During the slaving operation the compass valid output will be invalid, this should keep the AP from selecting heading mode.  However, if someone has wired around the compass valid input to the flight computer you could select heading mode with the compass system still trying to slave and you would have a oscillation in flight.  Once the system slaves the problem would go away.  Something to look for during the oscillation would be is the heading flag on the HSI still in view?

Best thing to try is see how the ap system does wings level without the compass system being used, so no heading mode just FD and AP on.  If it still oscillates the compass system is not your problem. 

[Aerodon]

On 1/3/2023 at 12:19 PM, Glen Davis said:

The problem is when I engage the AP in the heading mode, shrlty after takeoff, the aircraft hunts left and right for about 5 minutes, then stops hunting.  From that point on it works perfectlty.  It's always and only when first engaged.  When I posted this problem to the group the largest majority of answers to what they thought the problem would be was the indicator. Therefore I found a replacement indicator to try before I went the more expensive route I bringing it to a shop.  Even on the ground, when I engage the AP, it hunts right and left.  After a few minutes it stops hunting.

I had something similar in my Seneca, replaced the roll servo.  I'm not sure you can test anything like this on the ground, its an issue of the servo / clutch / feedback loop not being correct.  

Aerodon

 

 

[Will.iam]

2 hours ago, Aerodon said:

I had something similar in my Seneca, replaced the roll servo.  I'm not sure you can test anything like this on the ground, its an issue of the servo / clutch / feedback loop not being correct.  

Aerodon

 

 

Jake at bevans  can they interface with the controller and the servos and can test individual components of the autopilot system. Showed me were my nav unit was sending the correct signal and the roll servo would respond to the correct signal this left the wiring harness the last component of the system as everything else worked fine with his test harness.