Greetings! Has anyone else successfully used a Fox Delta ST2 interface with a Yaesu G5500DC?

With the ST2 unit off and the GT5500DC on, I have having issues with high voltage (~15V) on GND and +VE, around 2.2V on GND and AZ, and then only about 1.1V on GND and EL. The ST2 will calibrate for AZ, but nothing at all on the EZ side. When I plug in the USB and power up the ST2, the voltage on EZ drops even further to about 0.8V

The Yaesu AZ and EL meter readings on the controller have been just fine throughout.

Any help or suggestions appreciated!