Electric trim not working, King KC 192 autopilot trim warming

[steve wilbur]

My manually operated electric trim intermittently failed gradually resulting in a trim failure warning on the KC 192 autopilot (which now doesn't work  ).  Manual trim still works fine.  Anyone see this before?  Is it likely a failure of the trim servo, a bad connection to the trim switch, or a problem with the autopilot computer?  Where is a good place to start looking?  If I can't sort it out, should I take it first to an avionics shop or a mechanical shop?

[carusoam]

Start at the trim servo and work your way back…

They wear… and OH isn’t a low cost affair…

There may be take-outs available… for trouble shooting…

Lots of BK APs being retired…

Best regards,

-a-

[GeneralT001]

50 minutes ago, carusoam said:

Start at the trim servo and work your way back…

They wear… and OH isn’t a low cost affair…

There may be take-outs available… for trouble shooting…

Lots of BK APs being retired…

Best regards,

-a-

So is it a DIY or do you needs a pro?

[StevenL757]

5 hours ago, steve wilbur said:

My manually operated electric trim intermittently failed gradually resulting in a trim failure warning on the KC 192 autopilot (which now doesn't work  ).  Manual trim still works fine.  Anyone see this before?  Is it likely a failure of the trim servo, a bad connection to the trim switch, or a problem with the autopilot computer?  Where is a good place to start looking?  If I can't sort it out, should I take it first to an avionics shop or a mechanical shop?

Steve,

I’ve run into this twice in my previous Ovation, and both times it turned out to be the pitch/trim servo.  The first time, I was able to replace the servo with an overhauled unit (about 4 years ago) for a relatively reasonable price - around $1,000.  The second time, the price was up over $2400 including labor, so I opted to replace the KFC150 with the GFC500 with yaw damper and never looked back.

[PT20J]

Jake @Jake@BevanAviation can probably tell you how to narrow it down. When mine did this, it was the computer. The BK autopilots will not work if anything is wrong with the electric trim system.

One nice thing about the GFC 500 is that it is supposed to revert to giving manual trim up and down annunciations if the electric trim system fails rather than locking out the autopilot (I say supposed because I haven’t personally verified this and I’ve been burned enough times by Garmin documentation that didn’t match actual operation). A GFC 500 is nice, but not an inexpensive solution.

Skip

[carusoam]

4 hours ago, GeneralT001 said:

So is it a DIY or do you needs a pro?

I would be having my avionics guy be doing the work… but identifying the culprit is often a DIY kind of thing…

I have a good Mooney avionics guy near by… who often deals in pre-flown avionics…

 

+1 for speaking with Jake… he is really helpful with identifying what the issue is… lots of experience to go with that….

 

 If you can narrow it down to which device isn’t working properly…. That is a great way to start…

PP thoughts only, not much of a DIY guy anymore…

Best regards,

-a-

[Jake@BevanAviation]

@steve wilbur If MET (manual electric trim) has stopped functioning it could be wiring issues but most commonly it is a issue with the trim voltage regulator inside the trim servo.  The KC192 actively monitors this regulated voltage and if it is out of mfg specs it will cause a PFT failure.  If there is no regulated voltage the KC192 will have no flashing trim annunciations during the pft, you will get a flashing trim fail at the end of the test and it will not allow the system to work.  Best place to start is to see if the voltage regulator is working in the trim servo.

At the trim servo pin A sends out the regulated voltage to the yoke switch, there is a parallel to the computer for the voltage monitor on P2 pin W. See prints for details.  If the trim servo has a good power source and a good ground it should regulate a voltage.  Depending on the dash number of the unit the regulated voltage for a 14V systems is 12+/-1VDC and for a 28V systems 26+/-1VDC.  If you are handy with a voltage meter check power and ground at the trim servo connector, if that looks good check the regulated voltage with the trim servo plugged in via backing pinning the trim servo connector, at the MET switch on the yoke, or at the computer connector. 

KFC 150 M20jk 14-28v.pdf