S-tec 55x Installation Manual Best Info

| Symptom | Manual Reference | Likely Cause | Solution | |---------|----------------|--------------|----------| | Autopilot rolls left constantly | Section 6.3.2 | Rate gyro drift | Re-zero gyro voltage (adjust R22 on SC-55x) | | No NAV capture | Section 5.2.7 | Missing “Valid” signal from GPS | Verify GPS output (Pin 12 voltage >4V) | | Pitch oscillation (“porpoising”) | Section 8.1.4 | Pitch gain too high | Adjust gain pot (clockwise decreases gain) |

With power off, measure resistance between each servo motor lead and ground. The manual specifies >1 MOhm. Any lower indicates a short. S-tec 55x Installation Manual

Cut all wires to length per the “Aircraft-Specific Addendum” (usually not in the base manual but provided separately for your tail number). Use Tefzel MIL-W-22759/16 wire. Solder D-sub pins per manual’s crimp specifications (do not use generic automotive crimps). | Symptom | Manual Reference | Likely Cause

Start with the rate gyro. Use a digital protractor to verify alignment. Then mount the computer and servos. Torque servo mounting bolts to the manual’s specification (e.g., 25 in-lbs for roll servo clamps). Cut all wires to length per the “Aircraft-Specific

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