297b preselect

[pkofman]

Today In the Bravo my 297b  altitude preselect decided to go to a black screen. I had several episodes  of black screen then working screen etc.  it was working then "poof" black screen .I dont recall any event that would have caused this .. I was not sure it the 297b was  still providing an input to the autopilot , but it was black then it came back to life then it died again. This is my second replacement unit .  there seems to be no warranty on the unit.. Ive changed most of my old radios and gps in this plane  but Im tired of  chasing the old stuff. the radios work great when they  work,, but if they fail it is a difficult situation. Does anyone have any immediate quick fix solution. Is there a reset for that unit given the screen is intermittent, and is there another product I can get to replace that box. ( Garmin or other ).... I still have the king kap150  autopilot in the plane

It would be nice to find an alternative ( updated avionics ) for  the preselect box if I could find one

thoughts??

 

Peter

[LANCECASPER]

There is no plug-and-play alternative unit to the KAS-297B other than replacing the KAP150 with a Garmin GFC500. However the KAS-297B can be repaired at a shop that does component level repairs.

 - - - 

If you're in a hurry this looks like a nice one: https://www.ebay.com/itm/185001689662

[mike_elliott]

Bevan Rabel fixed mine up many years ago for the same thing.

They are on the list I believe

 

 

 

[LANCECASPER]

18 minutes ago, mike_elliott said:

Bevan Rabel fixed mine up many years ago for the same thing.

They are on the list I believe

https://bevanaviation.com/location-contact/

@Jake@BevanAviation

[Pinecone]

Shade the display and see if it just is very dim.  I thought mine was dead when I did my transition training, but realized it was just stuck in dim.  You can also shine a flashlight (cell phone works fine) at the photocell at the top left and see if it brightens.

If so, it needs the photocell replaced.

Larry at Sarasota Avionics (Sarasota location) can do this repair.  I recently had him fix mine while there for some other work.

[Jake@BevanAviation]

We do not work on the KAS-297B.  I would suggest Mid-Continent Instruments, Duncan Aviation, or Southeast Aerospace for evaluation/repair.  To my knowledge the only box that works in place of the KAS-297B is a GAD43e that is paired with the G500/600 glass displays.

[pkofman]

Hi @Jake@BevanAviation do you know if the 297 is failing or in error would it cause the test cycle ( pushing) the trim button to fail and not complete. In my case the display will go black or it’s on and readable. But since this started the a/p (trim) button test does not always complete.  Would a failure of the 297 cause this response from the a/test cycle? 
thank you peter

[Jake@BevanAviation]

@pkofman I have not personally seen an instance where a failed KAS-297B would cause the KC19X flight computer to not pass PFT. The alt pre-selector was an optional system that could be added to the KFC150 system. It does get information from the flight computer system for oscillator and digital data. There is the possibility that if the unit were pulling the oscillator low that it could cause the flight computer to fail a PFT. If you wanted to isolate the KAS-297B out, I would just unplug the unit and then try the PFT on the flight computer.

I would not be surprised if the flight computer you have has capacitor leakage in the power supply circuit. This is a known issue with units manufacture from 1993-1998. Are you getting the 12-13 flashes of AP on a successful completion of the PFT? Also, when the unit fails the PFT do you get the flashing trim fail annunciation or is the unit completely dark?

 

[Will.iam]

Also check your trim switch on your yoke. Might just be coincidence of the 297b My trim switch was worn to the point that the switch would not return to center and the autopilot would fail the test. Once i got the switch repaired I haven’t had a test fail since. 

[pkofman]

Thank you all for the advice.

I had it checked out at the shop and the end result was surprisingly simple,  The connector had come loose on the back of the unit,  but not detached, ( ever so slightly  loose ) and because there is so much stuff back there, one shop found it, and another did not! It took someone who knew the plane ,an a mirror, to get a good visual on the connector ! From what i understand the intermittent nature of the failure on final had something to do with the weight of the cable when descending, which would pull down on the harness causing the power to come off, and my screen to go black. That is why it seemed ok in flight, but i lost the screen when on approach. I dont know if that is correct of not, but maybe it will help others in the future...By the way  this turned out to be the cheap  fix option, and that does not happen for me  very often!

[carusoam]

Great follow-up PK!

Thanks for sharing the details.

Best regards,

-a-