There are mainly 3 parts on the cell phone screen you need to consider when determining screen damage:
- Glass panel: the protective glass layer adhered to the rest of the screen.
- Digitizer (Touch Pad): The sensor for your touch input, it look like a thin layer of metal that goes around the screen, and it have a flex cable coming out of it.
- LCD: The actual display that shows you all the colorful pixels.
You want to look for LCD damage first, turn your screen on and switch between different color backgrounds, some damage is more obvious on top of one color than another.
This LCD have a huge area that's broken.
This one here has a black spot on the LCD:
This one also has a black dot, but it is behind some broken glass and is harder to see:
To fix LCD problem like these, you will need to replace the whole screen.
Most Samsung devices have a testing mode you can use for testing screens, you can open it by dialing *#0*# in your phone app.
Not only you can change the screen color here, you can also use this to test the digitizer as well:
If you have an iPhone or any other brand, you can try drag an icon around the screen to test your touch input.
If your input isn’t responsive, or it breaks off at a certain area on your screen, then you need to change the digitizer and the glass panel.
If you didn’t find any display issue, or touch issue, the only thing broken is the glass panel, then all you need to do is to replace the glass panel.