Have any of you experienced this sort of problem
with your S-Tec units?  What was the cause and how did you fix it?

Yes, I previously commented on this problem.

 

1. The altitude sensor can fail - mine did, check the voltage output whilst sucking on the static port.  S-Tec bulletins (at the S-Tec site) can provide appropriate info or call S-Tec.

 

2.  The servo can become less effective from a build up of carbon at the brush armature interface.  This requires an increase in voltage from the computer to cause movement and the result may be too much correction.  There are three ways to alleviate this problem:

 

a. Using your wiring diagram, pull the computer D-Sub and apply about 40 VDC to the pitch servo pins for 10 minutes, reverse the power and do it again for another 10 minutes.  This will annually improve performance.

 

b. Carefully remove the servo cover, and then the brush holding mechanism.  Clean the brush and armature. Polish the armature. Reinstall. I have done this without removing the pitch servo.  This is the "long term" fix.

 

c. Replace the whole system with a TruTrak.