S-tec 55x Installation Manual !!link!! Site

Apply power. The manual’s Table 4-2 lists BI light sequences. A steady “S-TEC” light means success. Flashing indicates a specific failure (e.g., rate gyro disconnected or servo stalled).

| 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) | S-tec 55x Installation Manual

With power off, measure resistance between each servo motor lead and ground. The manual specifies >1 MOhm. Any lower indicates a short. Apply power

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). Flashing indicates a specific failure (e

Introduction: Why the S-TEC 55x Installation Manual Matters

| Pin | Signal | Function | Wire Gauge | |------|----------------------|-----------------------------------|-------------| | 1 | GND (Power) | Chassis ground | 18 AWG | | 3 | +14V or +28V | Aircraft power (through CB) | 18 AWG | | 12 | NAV/GPS Valid | Input from GPS (active high) | 22 AWG | | 14 | Heading Bug CW | Potentiometer wiper | 22 AWG shielded | | 27 | Pitch Servo CW | Motor drive output | 20 AWG | | 38 | Yaw Rate (Gyro) | Analog voltage (1.5V +/- 0.2V at level) | 22 AWG shielded |

Connect power and ground first. Then connect the gyro, servos, and annunciator. Leave NAV/GPS connections for last.