Aircraft is a 1976 PA28-181 with a Autocontrol IIIB (Century IIB). The radio coupler is connected to a G5 using the GAD29D per the Garmin STC. This was installed as well as a replacement Attitude indicator (overhauled by AQI) around 6 months and 150hrs ago. It has worked phenomenally well in that time. I recognize this is an old unit but it does 90% of what I want and I'm not sure if I want to spend the ~$10k on the GFC500 at this time so I would like to fix this.
Here are the symptoms:
- In the ground and in the air, with the AP switched on at the console and HDG OFF, the yoke rolls hard over to the right.
- This occurs regardless of the position of the roll command knob.
- If heading mode is enabled, no movement of the heading bug in any direction will impact this.
- From the bottom of page 31 of this service manual, the troubleshooting guidance indicates to "check console amp's output and horizon". This was what I expected based on my understanding of how the unit functions but I also would consider that the servo or roll signal filter could have failed.
Here are my questions:
- Is there a way to "check the console amp" without special tools? Is there a common failure that can be checked visually or with a multimeter?
- Is there a way to check the AI output or roll signal filter without special tools? Example - if CD18 (from console to roll signal filter) is unplugged from the roll signal filter should the roll command be nullified or would it be expected to go hardover?
- Is there a failure mode not noted here where the servo may get stuck trying to deflect in one direction?
Here are the symptoms:
- In the ground and in the air, with the AP switched on at the console and HDG OFF, the yoke rolls hard over to the right.
- This occurs regardless of the position of the roll command knob.
- If heading mode is enabled, no movement of the heading bug in any direction will impact this.
- From the bottom of page 31 of this service manual, the troubleshooting guidance indicates to "check console amp's output and horizon". This was what I expected based on my understanding of how the unit functions but I also would consider that the servo or roll signal filter could have failed.
Here are my questions:
- Is there a way to "check the console amp" without special tools? Is there a common failure that can be checked visually or with a multimeter?
- Is there a way to check the AI output or roll signal filter without special tools? Example - if CD18 (from console to roll signal filter) is unplugged from the roll signal filter should the roll command be nullified or would it be expected to go hardover?
- Is there a failure mode not noted here where the servo may get stuck trying to deflect in one direction?
Last edited:
