Next S-TEC disaster!
After the low quality servo was repaired, 40 minutes into the flight in calm air, the electric trim stopped working. The AP detected the condition and provided manual trim commands so better than the last fault.
Turned out the fuse on the trim board inside the pitch "computer" melted. I replaced the fuse and tried again. Looks like the board runs the trim servo in one direction without indication and as soon as it gets an opposite direction trim command, it shortcuts the circuit and the fuse blows. Looking at the circuit, there is no protection against driving the servo with both polarities at the same time, i.e. shortcut the circuit. Amazing design.