Depends greatly on your level of experience with electronics repair. In rough order of difficulty/complexity: Simply remove the module, wipe down the connecti

Depends greatly on your level of experience with electronics repair. In rough order of difficulty/complexity: Simply remove the module, wipe down the connections with alcohol, reassemble. If there's a 'zebra strip', gently peel it off, clean both ends, reassemble. If you see improvement, repeat with care until all segments are alive again. Replace the backlight. Depends on the exact module, but sometimes they're just simple LEDs that can be replaced. Ensure the polarizing filters still work. You'll need to research LCD polarizing, it's more complicated than I care to explain in a HN comment. They can degrade and sometimes need replacing. Beyond this, you're looking at an electrical fault or the display is just dead. You'd have to start probing the display driver to examine the signals. A good starting place is to replace all the electrolytic capacitors. Barring that, you likely have a bad display module. Sometimes you can test them by connecting some pins to ground and just touching other pins with your finger. The static electricity in your body can be enough to flip segments on