Electric trim relay - Where is it located????

[RocketAviator]

Hello all, sadly long time no visit to MS for me...

I am in need of some (ok maybe a lot of) help, during my BFR (yea I know they may call it something else now) this past Wednesday during a hold to an approach I utilized the CWS then disconnected the autopilot.  The electric trim never worked again. 

So today I decided to see if I could figure out why.  I was by myself and could not be in both the tail section and the cockpit at the same time but I am sure I could hear the trim motor running.  The autopilot will self test and pass like normal.  I have not attempted to see if the autopilot will function in flight.  I do not hear what I recall as the slight noise of a relay when I try to run the trim.

Today I engaged the autopilot on the ground and could hear a distinct clutch engagement of some servo but it is not the trim servo as the control wheel does not move.  Also during the self test I believe I can hear the trim servo test fwd and rev as it normally does.

As I spent most of the day removing the switch, checking the wires and connections in the yoke etc.  I disassembled the switch which comprised of a very simple set of 3 type C micro switches, fed by +12VDC, two wires on what I believe are the clutch and autopilot feedback on one switch and cross connected to the adjacent two same configuration switches in reverse settings feeding two wire to what I presume are direction control for the trim servo.  On the side I would never pay 500 - 800 for this switch it is very simple setup, I would suspect it can be easily rebuilt for 50 or less.

SW1, 12vdc center post (NO), Green wire top post (C=common), White/B wire bottom post (NC)   (I call this the clutch / power control switch)  The green wire (C) and the White/B wire must be a connection in order for the autopilot to complete and pass its test.  Does not matter the position of the Up / Dwn switch as the (C) of SW1 provides 12vdc to both of the (NO) contacts on the adjacent switches.

SW2 & SW3 have identical wiring that allows for positive and discrete contacts with used in conjunction with SW1 in either position.

What I am looking for is any info on the clutch relay or whatever is utilized to control the servo clutch on for the electric trim.  Where is it located what does it look like.  Is it the disconnect relay if you will similar to what I had on my Century Auto Pilot in my Piper Saratoga?  Any tips and recommendations on where and how to troubleshoot this problem would be greatly appreciated.

Thanks in advance,

Lacee / RocketAviator

[Cardinal767]

I had the exact issue with my KFC 200 autopilot engaging but will not trimming. I did exactly what you did. The avionic shop said it was the trim switch. Like you I didn’t want to spend $900 for a switch. I finally rang the wires out from the switch in the yoke to the connector under the panel. Bingo, where the wires come out of the forward end of the yoke shaft (under the panel) I found a broken wire. The wires come out the side of the shaft and are being worked back and forth as the yoke is turned side to side. Mine was clamped and spiral wrapped. Once I removed all this to expose the wire, the wires looked intact except for one that looked kinked. The outer cover looked good, but the wire inside was clearly broken when I moved the wire. This wire went to the RED (clutch) side of the split switch. Two minute solder sleeve repair and back together it went. $900 saved

Yes, the three micro switches in the trim switch assembly can be found. They are MIL spec switches that cost $17 each. But an avionic shop will not replace them because the assembly is a PMA’d part. FYI, the King switch had 3 jumper wires soldered between the 3 switches and two tiny straight springs that center the toggles.

Edited March 11, 2018 by Cardinal767

[RocketAviator]

Thanks Cardinal767, I carefully checked the area of the yoke tube.  I am going to reassemble the strain relief to a better angle but other than that the conductors appear to be in good condition.  I will ring them out to the first connector to be sure.

Do you know where or if the system has a clutch relay?

Thanks in advance.

[Cardinal767]

I have a King KFC 200 autopilot. I've only had this aircraft for a year, the autopilot had this issue when I bought it. I followed my ear to find the relay under the instrument panel above the pilot side right rudder pedal, near the firewall, not far from the connector the wiring from the yoke trim switch connects to. 

So here is the time line. Since I bought it, I could fly with the autopilot engage but would have to hold the CWS button down to move the trim wheel by HAND. Once I fixed the broken wire I was able to trim with trim switch BUT the autopilot would still not automatically trim. Avionics shop said it was either the computer or the trim servo. I took the cover off the elevator trim servo in the tail and found the control force sensing switch broken. I couldn't miss it, it's a small piece brass that ended up jammed between two switches. King does not sale parts to repair stations any more so guess what, I had to send it in for a flat rate repair of $1800. But I did save $900 on the trim switch.

Question. Does the elevator trim constantly trim up and down in cruise? Mine does now that everything is working.  

 

I hope this helps    

[RocketAviator]

Thanks what did your relay look like was it the typical ice cube relay or some special purpose relay?

Yes I suspect you could say my trim moves constantly in flight but the aircraft does not porpoise and you have to have your hand on the trim wheel to know it's even moving.  

[carusoam]

Hey Lacee, nice to hear from you again!

Best regards,

-a-

[RocketAviator]

Still looking for any information on where and what the relay looks like if anyone knows....

Heck is there even a clutch relay?

Thanks

[Cardinal767]

Easy Rocket Man, I had to fly today.

The picture is of the relay (grey square) ice cube I hear clicking when the trim switch is activated. The relay is at the top of the firewall on the pilot side. Windshield rivets and terminal strip on the pilot side are clearly seen. 

The PDF file is the King installation wiring schematic. No, I do not have the complete set

Your description says you can hear the trim motor running when you press the test and when you use the trim switch? Have you looked at the trim servo? If you have not notice them, open the tail access panel and look to the right.  There are two servos (black cube/cylinder) in the tail, (forward) one with a chain running to the trim tube (centered at the bottom) is trim servo and the control servo is about a foot behind and above that one. Being the trim wheel will not move when the AP is engaged, sounds like its that part is working. 

Hope some of this helps

Mooney AP disc.pdf

[RocketAviator]

Forgive my impatience Cardinal767... 

I sincerely appreciate the assistance.

I plan to see what I can find tomorrow after work.  Have a formation clinic I've committed to in San Marcos the 23rd of this month.

Your profile shows you from TX CO CA and you know me as RocketMan... So I'm assuming we have crossed paths in the past?  Did we attend a formation Clinic or the Caravan to Oshkosh together?

Thanks again.

 

[Flymac]

Had the exact same issue just corrected this past summer...electric trim stopped physically moving the tail, pressing the trim switch in either direction i could clearly hear the relay(mounted inside, upper left firewall) engaging, and i could hear the trim motor running back in tail.  Problem was also intermittent.  

There is a solenoid that engages (pulls down) a gear reduction assembly from the trim motor to the trim tube right behind avionics shelf.  I had a few of those small blue tyco/amp connectors at multiple points between the motor assembly and up to where it ultimately ran back into cabin...i checked at each point moving fwd to rear (with trim switch engaged) until i found one of those connectors dropped the 12V that closes that solenoid, the socket\female connector had simply worn loose over the years and was intermittently making contact with its mating pin! Solenoid wasnt getting its 12V to engage drive train while the other pins were still fine passing the 12V to the trim motor, as they  are split out.

sounds like you have exact same issue to me, start at your connections, or put a voltmeter on the solenoid to see if its getting power with trim engaged, if its not, work your way forward.

 

[Cardinal767]

On 3/13/2018 at 6:44 PM, RocketAviator said:

Forgive my impatience Cardinal767... 

I sincerely appreciate the assistance.

I plan to see what I can find tomorrow after work.  Have a formation clinic I've committed to in San Marcos the 23rd of this month.

Your profile shows you from TX CO CA and you know me as RocketMan... So I'm assuming we have crossed paths in the past?  Did we attend a formation Clinic or the Caravan to Oshkosh together?

Thanks again.

 

No sir, I haven’t had a chance to attend any clinics or other gathering. Sadly I’ll be in Denver the weekend of the 23rd. I live in Waco, TX but I mostly work in Denver and Carlsbad, CA. My 232 is my commuter 

[RocketAviator]

Thanks my "Call Sign" given by the Mooney Caravan was changed to RocketMan so I assumed that was the association.  

Update, I've made contact with Autopilot Central and Mooney after checking for hours..... To learn there is no interposing relay!  Last night I received and now have the complete electrical schematic for my specific model.  Still troubleshooting.  Hope to pinpoint the problem today or I may not make the 23 clinic myself.

Hope to meet you in person sometime, fly safe.

 

Edited March 17, 2018 by RocketAviator

[amillet]

The Avionics Shop at Tacoma Narrows Airport (KTIW) replaced the internal micro switches in our yoke trim switch several years ago.

[Cardinal767]

4 hours ago, RocketAviator said:

Thanks my "Call Sign" given by the Mooney Caravan was changed to RocketMan so I assumed that was the association.  

Update, I've made contact with Autopilot Central and Mooney after checking for hours..... To learn there is no interposing relay!  Last night I received and now have the complete electrical schematic for my specific model.  Still troubleshooting.  Hope to pinpoint the problem today or I may not make the 23 clinic myself.

Hope to meet you in person sometime, fly safe.

 

Fly safe also. With the schematic you can go back to the original point. Everything stopped working after you pressed the CWS button. I flew my 232 for weeks while parts were being repaired.  From your description, I’m thinking you can still move the trim wheel by hand? 

[RocketAviator]

Yes I can but don't prefer it especially when flying formation I have to take my hand off throttle... Can be done, have done it just prefer not. 

Thanks for your help and I now have several schematic for kap 150 and the Mooney specific schematic for around 25-0600 - 25-0900 I think if anyone needs them.

[RocketAviator]

Found the root problem, learned more than I ever wanted to know about the so called trim servo and the manual trim control..... for the KAP150 with the KS179 including all the pinout test points along with a great deal of the guts of this so called servo!

will post a follow up with schematics and lots of pictures when I have a chance in hopes it could help someone else in the future.

 

 

[RocketAviator]

Thanks Andrew, will check it out.  

[Phil EF]

Wow! Just read UK pilots saga. (Above link)

Really happy to have my Century 41

[larryb]

That article caused me to specifically avoid the KFC225 when I was shopping 2 years ago.