Nokia Lumia 520 Memory Card Not Accept Error Solution
https://gsmfixer.blogspot.com/2014/11/nokia-lumia-520-memory-card-not-accept.html
Nokia lumia 520 MMC corrupted problem creates when memory card filter ic damage and not works properly. If you have new ic then problem can be solved by changing mmc ic only. If ic not available then remove mmc ic and apply jumpers to solve this problem.Here is a diagram in which all points are traced and shown with different color lines. Observe diagram and apply jumpers like diagram below.
Diagram source : www.mobilerdx.com
Nokia 520 memory card ic jumper diagram is best solution to solve this problem.