The front screen of the VENTURE has small buttons on the back that control various screen functions like brightness. This tutorial explains what those buttons do.
Below is an image of the VENTURE front screen without the aluminum back plate (which has holes exposing the buttons). The buttons have been highlighted with a red box:
The functions of each button from top to bottom are:
Accessing the menu brings up several options including Brightness and Contrast.
The volume settings will have no effect as there are no speakers connected to the screen.