PCB, ASSY, STX INVERTER I/O BOARD I/O Inverter Board. Input/Output Inverter board. Allows the transmitter Inputs to be controlled by positive logic. Needed with Gen II if you want to invert logic. Not needed in STXe units.
STX-LP Gen 2 GPIO requires a negative logic / signal to ground for remote control. To use this transmitter with a positive logic / +5V signal system, such as the FA-2 Main Alternate Controller, the +5v signal must be converted to GND.
The 919-4001 I/O Inverter Board accomplished that task.