[Bob Cook]

400 and 400A have basically the same computer and both are two axis I believe.

In any case, by pulling using the knob only steering, everything is eliminated as far as directional control.

If you cannot HAND steer it with the knob and pilot engaged then there are a few things to look for.

1) power supply +/- voltages at the computer.
2) reference voltage (going to feedback pot at the servo) which is -10V.
3) broken or bad connection between the feedback pot and computer or a dirty and intermittent feedback pot at the servo.

Sounds like dirty connectors or dirty pot. You can swap the electronics from the elevator servo to the roll servo as they are the same.

Give me a computer part number and servo part number and I will give you more feedback.

As mentioned earlier the power supplies gave problems. It could also be dirty contacts on the printed circuit boards in the main computer itself. The computer should be located at the back of the aircraft, in the headliner behind the pilot and behind the flap actuator motor.

The engage switch is in fact a solenoid that is actived by an archaich series of "and gates" one of which is power. If you are having problems engaging the switch and staying latched it is most likely the power supply.

check the connectors.

bob