STEC 30 Altitude hold issue

[Pa28-140]

I'm having an issue with my altitude hold on the STEC 30 autopilot. I do not have electric trim so I manually adjust to up/down trim notices. The issue is that after a few minutes I get a trim down indication that I adjust for, then a trim up indication that is followed by both trim up and trim down lights and aural alarms. Even when I turn the altitude hold completely off, the up/down lights and aural alarm continue. My shop sent the pitch computer to STEC but they could find nothing wrong. This same issue happened about 4 years ago. What solved it was a hard landing in a stiff crosswind. After that, it performed flawlessly until recently. My avionics shop pulled the pitch servo today, but they don't think that is it. Any suggestions (other than another hard landing)?

 

[bnt83]

Sure sounds like some sort of board level failure to me. I'd call autopilot central and ask

 

[Pa28-140]

Sure sounds like some sort of board level failure to me. I'd call autopilot central and ask

Thanks. I’ve emailed them several times but no response. May have to call and see if they are interested in trouble shooting the issue.

 

[flyingcheesehead]

S-TEC hands out business cards at Oshkosh with troubleshooting steps for both pitch and roll axes of autopilots. The very first item on both lists is "check your rigging." Apparently they get a LOT of autopilots back that check out just fine.

http://genesys-aerosystems.com/blog/the-ups-and-downs-of-autopiltot-troubleshooting