KAP140 off track and heading

Axelaxe wrote:

Any idea what this might be?

Hidden somewhere will be a turn co-ordinator which supplies the roll rate signal. With the aircraft level in roll and aircraft powered-up, check that it shows wings-level and that the slip ball is centred. What happens is that an error/offset in the TC output will result in a compensating offset in the mode you’re in. This is exactly the same as happens with an S-TEC autopilot

Then carry out the roll null adjustment per the maintenance manual (the pot is on the face-plate to the right of the display):

For the roll and pitch axis null adjustments, adjust the pot until 0 +
.020 volts DC is measured across the servo drive pins D and L of the
roll servo and the pitch servo harness connectors. This is
accomplished as follows: First, allow the FCC to pass pre—flight test;
then unplug the servo connector from the aircraft harness. Next
apply an aircraft ground to pin K of the harness connector. Now
connect the digital multimeter across the harness connector pins D
and L to monitor the servo drive voltage.
1. Engage the autopilot by pressing the “AP” button on the FCC. The default ROL mode
must be selected, i.e. the HDG, NAV, or APR modes are not engaged. Using a DMM,
measure the DC voltage across pins D and L of the roll servo harness connector.
Adjust the pot until a value of 0 + .020 volts is measured. If you reach the end of the
pot travel before nulling the servo drive, disengage the autopilot, turn the pot fully to
the opposite stop, and re—engage the autopilot. The roll null adjustment emulates a
four—turn pot by allowing this method of “resetting” the pot adjustment range. This
adjustment compensates for offsets in the roll axes, including the turn indicator.
Continue turning the pot to null the voltag