Test button in Extended Tuning page of Antenna Tracker not working

I am building an Antenna Tracker using Pixhawk as AT controller flashed with AT V1.00.
Pan and tilt servos are connected to outputs PWM1 and PWM2 of Pixhawk, and powered by 5V.

After connected to MP 1.3.61, the 2 servos do not move after moving either the yaw or pitch slider, followed by pushing the TEST buttons.

Pls advise what has gone wrong. If I replace the Pixhawk with APM2.6 as AT controller, the TEST buttons do work.

Any help is deeply appreciated.