Samsung Galaxy Z Flip 4 (F721) - Black Screen Repair Guide

The problem

Screen Goes Black After Replacement After replacing the screen on the Samsung Galaxy Z Flip 4 (F721), the display may turn black shortly after powering on, even though the phone is still running.

Why it happens

The replacement screen frame may have a different or incompatible magnet, which can interfere with the phone's fold detection sensor and cause the display to turn off.

How to fix it

Locate the magnet in the replacement screen frame, as indicated by the red circle in the image below. Remove the magnet from the replacement frame. Transfer the original magnet from the customer's old screen frame to the same position. Secure the magnet in its original orientation and test the phone before completing assembly.

n frame.This can resolve black-screen issues caused by incorrect magnetic fold detection. If the issue persists, further diagnosis is required.