Why would a APS-80 in a Westwind II give TRIMA and TRIMB fail?

Aircraft is out of trim at AP disengage, so that means it is a trim problem, not a indication problem.



from “OldAutopilots” cd

In aircraft types that do not provide a horizontal trim rate feedback signal, the APC trim
command + output voltages are fed back into the APC trim rate input ports, and the trim system
is assumed to move when commanded. If the pitch trim system does not move when commanded, the problem will soon be apparent to the crew, because a continuous mistrim
annunciation will result.
The APC-80 contains trim monitoring circuits to determine that the trim circuits and trim system
is responding correctly. The monitors detect opposed trim, inoperative trim, or trim motion in the
wrong direction. The trim monitor provides two trim fail outputs, A and B. Each controls an
external relay, either of which removes power to the trim circuits in the APC and illuminates a
trim fail annunciator. Trim failure annunciations are latching and require correcting the problem
and re-engaging




Right side of the page.

Check 4 diodes, check trimrun relay

Check Hstab trim time stop too stop.

It is the APC that generates the trim fail, not the APA.


????how does the Main servo tell “out of trim” force….??motor current????