The assembly, even before switching on
The first reflex is to hold the screen in your hands. You check whether the hinges are properly installed, whether the gasket is correctly positioned, whether the housing has been properly re-anodised, and whether all flex cables and connectors are in good condition. The gasket must be smooth, even, and slightly higher than the bezel to protect the panel. The polariser must be perfectly bonded, without the slightest bubble or lifted area. A careless assembly here means a screen that comes back to you under warranty.
The 10-second move: grazing light along the edge — even gasket, well-aligned bezel, no flex cable sticking out or trapped under the frame.