Electric trim switch

[timpercarpio]

We have owned a '78 J for about a year and a half. During that time the electric trim worked intermittently. I had the trim motor checked, all the contacts checked and replaced the trim switch. This is not the split switch. It still only works intermittently. I have to push down on the switch to activate a relay, then push the switch forward for nose down or pull back for nose up. It almost always works on the ground, but not all the time while in the air. I'm taking the airplane in to trouble shoot in two days.

Any suggestions would be appreciated. Thanks.

[orionflt]

Defiantly sounds like in intermittent connection, and they are the hardest to troubleshoot. Double check your ground connection and all connectors making sure they are not loose or damaged, the next thing to look for is rubbing and chaffing of the wires. The air plane flexes in the air so and if you have a loose connection or an intermittent ground you will get the condition you are experiencing.

[jetdriven]

There are two diodes in the circuit, if its a Century trim system. Both of ours were broken and we had the same symptoms. They are located on the right side of the cockpit, inside a clear plastic tube, zip tied to the fuselage tube just forward of the door.  Check those.

[201er]

If it makes you feel any better, I keep getting problems with mine too. Finally had it fixed after spending a ton overhauling the trim motor and having switches replaced. It's a wild goose chase.

[timpercarpio]

Thanks, I'll check out all of your suggestions. I'm scheduled with an avionics shop on Wed

[ALP]

I hate chasing gremlins!!

I have a KAP150 that keeps having problems. Previous owner had trim servo serviced, and ap head sent back to Honeywell. System worked well for 6 months, I started having problems during "test" - unit would just keep beeping. Recycling electric trim switch (on panel) helped. Replaced switch and system worked great - for a while. After a while ap would not disengage w/o pulling breaker (intermittent of course). Found a bad transistor in head unit and replaced - worked great. Last week descending thru turbulence circuit breaker popped. Now the breaker trips immediately.

I'm scheduled at the avionics shop next week. I am hoping that we can find the problem since the breaker trips right away.

Which autopilot unit do you have? Let us know what you find.

[N201MKTurbo]

Mine does the same thing. Mine has a bad connection on the plug that goes to the disconnect relay. If I wiggle the plug I can make it work and not work. The contacts look good, at this point I think it is the solder joints inside the heat shrink of the plug.

[Jamie]

After seeing the price of mine, I stopped using it. And, I'm surprised to find that I'd much rather use the trim wheel anyway. $800 for a switch ('81 J) is just stupid.

[aaronk25]

Check on the bottom left side of yoke where all the wires hook up at the harness. Mine had same issue on my 77 and the wires were pulled pretty tight which caused a wire to pull back a but and cause a intermittent issue......let me know if that fixed it......

[AlanA]

I ended up replacing my switch because I like everything to work that is suppose to work, however because it was sooooo expensive to replace it ($600), I find myself afraid t use it for fear it will go out again. It works now but I mostly just use the trim wheel. Ridiculous that that part should cost so much. Must be made by NASA.

[flyboy0681]

After seeing the price of mine, I stopped using it. And, I'm surprised to find that I'd much rather use the trim wheel anyway. $800 for a switch ('81 J) is just stupid.

 

As many of you have read here, I had two (harrowing) incidents early in the summer where I had unexplained runaway trim after takeoff and it turned out to be the trim switch was intermittently sticking when applying nose down position.

 

Our repair was north of $800.

[Jamie]

My first though was "pull the breaker", but I knew when I thunk it that finding the correct breaker would be nigh impossible. I assume (hope?) shutting off the master would stop the trim motor? What is the correct procedure for that?

[flyboy0681]

My first though was "pull the breaker", but I knew when I thunk it that finding the correct breaker would be nigh impossible. I assume (hope?) shutting off the master would stop the trim motor? What is the correct procedure for that?

 

For me the situation was subtle because the motor moves slowly. I didn't really notice it until the trim was in full nose down position. If you are able to catch it in motion then simply flip the "ELEV TRIM" rocker switch (far right on J's) or override the system by turning the trim wheel in the opposite direction. This should disengage the electric trim entirely.

[Marauder]

My first though was "pull the breaker", but I knew when I thunk it that finding the correct breaker would be nigh impossible. I assume (hope?) shutting off the master would stop the trim motor? What is the correct procedure for that?

 

Put one of these on the breaker: http://www.lkdaerospace.com/media/17972/LKD_CircuitBreakerCollarsLockoutRings2013.pdf

[flyboy0681]

Put one of these on the breaker: http://www.lkdaerospace.com/media/17972/LKD_CircuitBreakerCollarsLockoutRings2013.pdf

 

This is how my CB panel looks since that incident.

[ArtVandelay]

On 9/30/2013 at 7:10 PM, N201MKTurbo said:

Mine does the same thing. Mine has a bad connection on the plug that goes to the disconnect relay. If I wiggle the plug I can make it work and not work. The contacts look good, at this point I think it is the solder joints inside the heat shrink of the plug.

I’m having same issue, can you remember where is the plug and disconnect relay?

 I realize this was 4 years ago, just to clarify, my etrim doesn’t work at all, or works fine in either direction.

TIA

[N201MKTurbo]

3 hours ago, teejayevans said:

I’m having same issue, can you remember where is the plug and disconnect relay?

 I realize this was 4 years ago, just to clarify, my etrim doesn’t work at all, or works fine in either direction.

TIA

It is on the firewall up high directly behind the pilots yoke shaft. It is a golden box about 2" square and 1.5" thick. It has one small connector coming out of the left side.

You can crawl into the pilots foot well. Turn the master on, actuate the trim switch while flexing the wires going into the connector. See if the trim starts working. You should also hear the relay click when you actuate the trim.

Good luck.

[bradp]

Here’s my story- 

You should be able to generally isolate where the fault is using a voltmeter and checking each part of the circuit - breaker - trim disconnect switch - relay - yoke switch - motor.  The mechanically manipulated thing is the most likely culprit   

 

[ArtVandelay]

It is on the firewall up high directly behind the pilots yoke shaft. It is a golden box about 2" square and 1.5" thick. It has one small connector coming out of the left side.
You can crawl into the pilots foot well. Turn the master on, actuate the trim switch while flexing the wires going into the connector. See if the trim starts working. You should also hear the relay click when you actuate the trim.
Good luck.

Wow, that’s some relay?!

[N201MKTurbo]

Looks like the hangar faries have been busy....

[ArtVandelay]

That isn’t what mine looks like at all. Mine is like Rich’s; a little gold box made by Century. 

Do you have 14 wire connections?

[bradp]

Any chance the previous owner was an electrical engineer?  Looks a bit too neat for your average hangar fairy but definitely a diy fix right there.  

[ArtVandelay]

I can order the relay and the socket for $15, for that price I’m just go ahead and order it. A schematic would be nice.

[pwhicks]

I'm troubleshooting a similar issue.  The UP trim works great.  The DOWN trim, I hear a click and the clutch engages which makes the trim wheel stick, but I can overpower it to manually trim down.

For a while it only worked in the air...now it is UP only and DOWN has a click.

My AP suggested the motor is tired.

'79 M20J has a Century II AP no Altitude Axis.

[cnoe]

The Century trim switch from that era has a stack of 3 microswitches under the yoke button that control its operation. That’s where my similar electric trim issues resided. It’s not an easy repair but following switch replacement I haven’t had a problem in 3 years now.


Sent from my iPad using Tapatalk