KFC 200 Trim Issue

[Northern Mooniac]

I just spent a small fortune getting all the services in my KFC 200 replaced, including the trim servo.

Now when I turn on the trim via the panel rocker switch it seems to work 50% of the time.

Sometimes it works perfect, sometimes I get a flashing trim light.

If I toggle the yoke trim switch I can hear clicking, so I think it's working ok.

Seems like the panel rocker switch is having issues, has anyone else seen this?

[ThorFlight]

I had been having a similar issue with my KFC 200. It had been happening ever more frequently over the past three years. Sometimes it would fail (flashing trim failure annunciation) immediately after disconnecting the AP, sometimes it would immediately fail immediately after startup, but then work later in the flight if I recycled the AP breaker + trim rocker switch. It was very frustrating as there wasn't a clear pattern of failure.

Over this period we pulled the trim servo, which tested fine, cleaned connections, switches etc., but the problem would continue. After again bringing it up with my avionics shop a month ago, they suggested that we try replacing the trim interrupt switch (the big red one). When they pulled it, they found it failed intermittently when bench tested. Since replacement I have had no issues.

FWIW the trim interrupt switch turned out to be a bit more sophisticated than I thought. As I understand it, in the normal (not pressed) state, trim current is directly routed via this switch to the trim motor. When depressed it opens the circuit to the trim motor to stop motor operation, and simultaneously closes a circuit to the KFC 200 signaling it to disconnect the AP+FD. When released the reverse happens, so in either state the switch must be functioning properly to avoid a trim failure.

[carusoam]

Great explanation, Thor!

Thanks for sharing all of the details...

Best regards,

-a-

[Steve W]

Yea, the trim interrupt/disconnect switch is a known issue on the KAP/KFC series. Here's the thread with the tear-down of mine from the KAP-150 which has basically the same failure mode:

https://mooneyspace.com/topic/25173-king-autopilot-disconnect-switch/

Edited December 14, 2019 by Steve W

[tmo]

18 hours ago, Northern Mooniac said:

I just spent a small fortune getting all the services in my KFC 200 replaced, including the trim servo.

Out of curiosity, have you considered the cost delta with ripping it out and replacing with GFC500 or some such?

meow!

[Bob Weber]

On 12/13/2019 at 11:11 AM, Northern Mooniac said:

I just spent a small fortune getting all the services in my KFC 200 replaced, including the trim servo.

Now when I turn on the trim via the panel rocker switch it seems to work 50% of the time.

Sometimes it works perfect, sometimes I get a flashing trim light.

If I toggle the yoke trim switch I can hear clicking, so I think it's working ok.

Seems like the panel rocker switch is having issues, has anyone else seen this?

Regretfully this is all too familiar. I can help with this, there are some simple checks that may point to the culprit quickly.

One of the most critical components of that system is the wiring and all associated components, switches, connectors, etc..

A thorough understanding of what the computer is looking for and what will cause the fail will go a long way here.

email some panel pictures to me if you would like, bobweber@webairconsulting.com

I think I can help you fairly quickly figure it out with a voltmeter, rather than more  unnecessary spending or time wasted.

Bob

[natdm]

Reviving an old thread here.

Had the exact same issue with my M20K 231 with KFC200. AP was working fine. I had always just turned off AP via the panel. This time I decided to try the disconnect on the yoke. It worked fine, but the next time I went to test the AP, it beeped 3 times, and then trim wasn't working, and had a flashing red trim light.

After working with my mechanic and looking at everything, I found this thread. Clicked the interrupt switch a few times, and it started to test OK again on the ground. Very weird. 

That said.. anyone have a replacement part number? (I don't believe it's the 633-MB2061SS1W01CC number from the 150). Bonus for a place to buy one.. It seems like I'd be fine if I don't use it, but I'd also prefer it to just be in good health and not intermittent, especially for IFR flight.