Electric trim inop

[Rrawlings3452]

The auto pilot is a century II

[OR75]

if the autopilot is a Century II ....

then , do you have an S-tec 60 PSS ? or no altitude hold and just autotrim ?

if you have an S-tec 60 pss, then you probably have a S-tec trim ( split switch)

if not, it may be a century trim ( not a split switch)

[Rrawlings3452]

The ap is a century IIB does this help?

[OR75]

The ap is a century IIB does this help?

no, it is not sufficient.

the century IIb provides horizontal navigation ( heading or radial tracking)

the trim is a vertical feature. it may or may not be associated with a vertical navigation autopilot ( like the 60 pss)

in any case, your trim motor will be in the tail cone , just behind the avionics rack. easy to identify as it will have a chain going around the trim torque link

[Rrawlings3452]

There is no altitude hold it does seen like the jacks screw may need lubrication, one other concern is the seat is somewhat broken down and when sitting there may be some pressure on the trim wheel.

[OR75]

then, i am thinking it is probably a Century autotrim ( not an stec with split switch as pictured above)

best is to check your aircraft maintenance logs

[Rrawlings3452]

Since the autopilot does not have altitude hold, it would seem to me there would be no relationship between the electric trim and the ap. Thus eliminating the ap disconnect mentioned previously. I plan to run several voltage checks this week I will keep everyone posted as to what I discover for future reference.

[N201MKTurbo]

Since the autopilot does not have altitude hold, it would seem to me there would be no relationship between the electric trim and the ap. Thus eliminating the ap disconnect mentioned previously. I plan to run several voltage checks this week I will keep everyone posted as to what I discover for future reference.

Actually there is a common disconnect relay for the electric trim and the autopilot disconnect.

[NotarPilot]

Does anyone happen to know what the P/N is on the trim motor? I’ve checked my M20J parts catalog, searched Google and the maintenance manual only refers to an Allied Signal (Bendix King) electric pitch trim system but I need a part number in case I have to OH mine as it is not working either.

[carusoam]

Notar,

This thread is a confusion of different APs and add-on altitude hold/electric trim systems...  Century/Stec...

Any idea what company built your autopilot?  And what model name it has?

Best regards,

-a-

[NotarPilot]

1 minute ago, carusoam said:

Notar,

This thread is a confusion of different APs and add-on altitude hold/electric trim systems...  Century/Stec...

Any idea what company built your autopilot?  And what model name it has?

Best regards,

-a-

I have the S-Tec 30 but I wasn’t sure if the trim system was an OEM item or an after market product associated with an autopilot system.

[bradp]

Look at my old trim thread for some guidance on how the system works and there a scrap of paper I scanned in that shows the button wiring diagram.  Common issues include the switch. Relay can go but it’s a pretty robust old school  relay, so less likely.  If /both/ the yoke switches are inop it’s either the power source, the relay, or the probably auto grade non OEM switch between the two yokes.  Worse case is the trim motor is burned, but I’d expect this to have tripped a breaker before burning.  You could very well have lost power / ground to one of the components up to and including the motor.  Get friendly with your voltmeter and you can trace where the issue is.  

If the trim system is operating, and the manual wheel is “stiff” it should have popped the breaker.   

A key step to the troubleshooting is do you hear a relay click when you engage

At some point someone modified your trim setup to do the dual switches   This is not OEM and kind of unnecessary as well as creates more hassle.   You should have the copilot switch removed.   There should also be a breaker switch or a manual throw switch that turns the whole system on / off for the 1977 century II system.  The good news is you have an extra trim switch!  

Anecdotally, I had a breaker keep popping and it turned out to be a shorted solder on the switch.  Resoldered the contacts and all was good.  The key was that the relay would intermittently engage with the switch depress, but at a certain rpm / cowl flaps open there was enough vibration to short the switch / no more relay : breaker pop (only in flight, which made troubleshooting more difficult).