Stec 55x

[lifendet]

Having trouble with my Stec 55x Autopilot in my J. Havent done any trouble shooting but all ideas are considered helpful. When in nav gpss mode or nav alone it doesnt follow my Gps flight plan anymore. It just wonders off on its own and also when I select Hdg it doesnt follow my bug either. In Alt and Vs mode it works but thats it. On start up the internal check shows no faults but it might be checking the control face itself and not the servos or maybe its just a electrical check to everything. Any ideas? Hoping my roll servo is not the fault..

[PaulM]

Have you run through the  POH pre-flight checks and the maintenance manual checks?

http://www.gvm.ch/documents/avions/pa32/sys55Xpoh.pdf
http://www.aeroelectric.com/Installation_Data/S-Tec/S-TecServiceManual.pdf

I would suspect a bad roll servo.. since all horizontal modes are bad.   But it could be your turn coordinator signal as well.   

With the standard test tools listed in the service manual a tech should be able to isolate it quickly. 

The tests in the manual (HDG hard left and right) with no yoke movement will probably be the servo. 

Also, when activated does it restrict the yoke?.. or no friction?..   No friction is definitely  the servo. 

[Marauder]

Having trouble with my Stec 55x Autopilot in my J. Havent done any trouble shooting but all ideas are considered helpful. When in nav gpss mode or nav alone it doesnt follow my Gps flight plan anymore. It just wonders off on its own and also when I select Hdg it doesnt follow my bug either. In Alt and Vs mode it works but thats it. On start up the internal check shows no faults but it might be checking the control face itself and not the servos or maybe its just a electrical check to everything. Any ideas? Hoping my roll servo is not the fault..

 

What’s providing the GPSS signal?

 

 

Sent from my iPhone using Tapatalk Pro

[lifendet]

4 minutes ago, Marauder said:

 

What’s providing the GPSS signal?

 

 

Sent from my iPhone using Tapatalk Pro

The gpss signal is direct from the 55x..

[lifendet]

10 minutes ago, PaulM said:

Have you run through the  POH pre-flight checks and the maintenance manual checks?

http://www.gvm.ch/documents/avions/pa32/sys55Xpoh.pdf
http://www.aeroelectric.com/Installation_Data/S-Tec/S-TecServiceManual.pdf

I would suspect a bad roll servo.. since all horizontal modes are bad.   But it could be your turn coordinator signal as well.   

With the standard test tools listed in the service manual a tech should be able to isolate it quickly. 

The tests in the manual (HDG hard left and right) with no yoke movement will probably be the servo. 

Also, when activated does it restrict the yoke?.. or no friction?..   No friction is definitely  the servo. 

When activated, once I notice it's not following my GPS I am able to use the yoke and control the Aircraft without disabling the modes or Autopilot. No friction whatsoever or fight against it. 

[Cruiser]

will it intercept and track a VOR signal ?

[PaulM]

33 minutes ago, lifendet said:

When activated, once I notice it's not following my GPS I am able to use the yoke and control the Aircraft without disabling the modes or Autopilot. No friction whatsoever or fight against it. 

In roll and pitch?...    Well if there is no friction and no difference if you hit the A/P disconnect then I'm going to say servo. 

It isn't clear if there is friction in the beginning, and it works for a while... then once you notice that it isn't tracking there is no longer friction.   

Run though the test sequences.. see what works and what doesn't. 

the GPSS signal would come from the GPS NAV... 430? 530?.. anyway since it doesn't work in all 3 horizontal modes I doubt it is the inputs.. but the outputs. 

[sgrooves]

Had a similar issue with my Stec55x. Turned out to be the ACU driving the Stec from my Aspen unit was bad. The ACU was replaced under warranty, labor wasn't cheap though.

[Mooney in Oz]

Had this happen to me too a couple of years ago. It turned out the roll servo over time had somehow loosened and come off it's mount in the left wing.

[mike_elliott]

6 hours ago, Mooney in Oz said:

Had this happen to me too a couple of years ago. It turned out the roll servo over time had somehow loosened and come off it's mount in the left wing.

That thing is a B*tch to R&R, very likely someone "neglected" to install the B*tch bolt. 

[thinwing]

That's why I love BK servos...the moter portion unbolts with two 7/16 bolts  leaving capstan still in place...

[lifendet]

Had some time today to figure out the problem. Opened the underwing panel and found the connector for the roll servo disconnected. Guessing some ruff turbulence shook it apart. Glad I took a look instead of having a Technician charge me..