Another great adventure with S-Tec..  Looking for an Altitude Transducer Part #0111.  After a couple of times sending the controller (S-Tec 50) back to replace a Pico Fuse at $150 per..( Had to be a short in  the wiring harness they kept saying, so replaced harness, the system still would not hold an altittude. This whole thing has gone on for several months.. Finally, today I read the resistance values of the Altitude Transducer itself and olah !!! factory then admitted that that was my problem,  I should have done it sooner, but not being a avionics wizard..Whine     Factory wants over a Grand for a new one, no repairs.  Same deal with their servos, as they age the motors tend to get into a "groove"  , buy  a new one or for about $800 they will install a new motor ..  Wa a pretty good system to start with, BUT...
   I post all this whining for those of you still considering an A/P purchase.. Anyway, any of you good people with a reasonable source, I would appreciate a call   Don Skeele  850-626-4946  N320J

Don,

 

I have an altitude transducer available - we can talk, I will call you.  But, your story may not end there.

 

1.  I had an internal AP fuse fail some years back (I think from an unusual electrical condition created in an very peculiar cloud).  While it appeared things were fixed, 2 years of pitch sensitivity problems ensued.

 

2.  The most serious problem was a circuit failure on the pitch board that was involved with the turn coordinator gyro tach - it ALWAYS raised the necessary ten volts on the tach pin, just like the tach would if it were up to speed.  If the gyro failed, the AP would still think the data was good.  The test for this failure is to pull the T/C breaker (on the ground, of course), initiate the AP start-up procedure and, after it goes thru its' checks, turn it to ready mode - If the green light is ON, you have an AP that thinks the gyro data is valid when it is not - not good in the clouds. 

 

3. S-Tec fixed the circuit component associated with #2 but the problems didn't end there.  Altitude hold became useless in any turbulence at all.  The pitch control started to do weird things over time - even send the elevator in the wrong direction.  S-Tec said the computer checked OK twice, but eventually replaced it on my demand because of all the testing, sensor replacement and motor replacement I had done (I had built a breakout box to allow me to test any interconnection line).  I am happy with altitude hold now.  I cannot emphasize enough that S-Tec is incapable of fully testing their own equipment.  BTW, the newer design level pitch board came with a sheet outlining the 6 or 7 components that can be changed to produce over 30 different sensitivity options - and you thought you were the only one with problems.

 

 

4. While the FAA will not let S-Tec service their $800 motor, you can.  The most common problem is carbon build up on the commutator.  The simplest fix is to supply up to 40 volts DC to the motor, in both directions, for a few minutes (36 VDC = 3 12 V batteries in serial) without engaging the clutch that connects the motor to the servo.  If that does not improve operation, the motor can be opened and cleaned if you are very careful.  Look at the harness wiring for the pins to use in this test.  I think I even have a made up a D-Sub for connecting to the servo D-Sub and you could easily make one too.

 

5. My roll motor responded to the operations in I outlined in #4 but the pitch motor eventually could not be resurrected -- maybe something I did on the umpteenth cleaning after which it worked fine on the ground, but not in the air.

 

6.  If taking out the S-Tec 50 and replacing it with a Tru-Trak wouldn't leave 3 large holes in my beautiful panel, I would do it.  Maybe next year.