Help troubleshooting autopilot pitch oscillation

nickmatic

Pre-Flight
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Aug 8, 2013
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Amsterdam, Netherlands
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Nickmatic
Troublesome problem here. I have a 1986 Mooney 252, equipped with a KFC 150 autopilot with KAS 297B altitude preselect. There's also a roll-steering adaptor but I don't have the model number handy.

For about a year once in a while (approx. once per flight) I'd get an excessive pitch up during climbout (vertical speed mode) or level flight (altitude hold). Sometimes I'd cancel autopilot and sometimes I'd just wait and it would come back to normal after a few seconds. Unnerving.

On my last flight in altitude hold mode the AP kept making pitch oscillations and corrections. Up for a few seconds, then down to correct, then back up again. Probably up and down 50-100ft each time. Not good.

Where would I start in troubleshooting this? Anyone seen this before?

Electrical connections? Autopilot itself? Rigging? Any advice appreciated!
 
Bad transducer or servo. My best guess is transducer if the servo runs smooth during trim.
 
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