The X-FADE/GATE is an audio/CV crossfader with a built in gate (VCA).
This module features CV over the crossfade between channel 1 and channel 2 along with a manual parameter to set an initial crossfade setting.
CV on the overall volume/attenuation is also a key feature with a manual control to set the initial gain setting.
This module is AC/DC coupled allowing it to process audio and cv signals. You can select AC or DC coupling with the onboard switch.
LM13700 IC's can be found HERE
Measure each sides voltage output with no source plugged. Turn the crossfader knob to the left, adjust trim pot until the output reads 0V. Repeat the process for the right side.