How to know whether it is the screen or controller is dead?

[tomatessechees]

Our 3 year-old Radwagon 4 suddenly decided not to start this week, just before back-to-school when we really need it.

All connectors are fine. I have checked the battery and connections with a multimeter. The fully charged battery is delivering 54V and the controller is sending 54V to the screen (bottom 2 pins on the 5-pin connector).

Is this enough to confirm that the controller is OK, but the screen is dead?