There are users of the Mr Beam machines who have had problems with the LCD screen fitted into the control panel. The issue being that the adjustable resistor, a tiny potentiometer on the back of the display (img1) has broken off, often leaving the display at its highest or lowest setting and unable to display text with any clarity.
On the single row of pins (NOTE there are three rows, the top two are used to connect to the Raspberry Pi) on the back of the board as can be seen below (img2) two of the pins can be shorted to bypass the broken resistor and set the display to a 50/50 setting, allowing text to be displayed.
A standard PC motherboard jumper can be used to jump (counting from the right!) pins three and four. These pins could also be soldered for a more permanent or durable fix.