NIGHTHAWK MR5200 NO WIFI (red cross)

i have the same issue as many others , that the wifi won't work (red cross) but with lan it does.

after some experimentation i may found the root cause.

do a factory reset. then configure all the necessary settings. after starting DO NOT TOUCH the WLAN logo in the display again. everytime after doing this, the wlan was irreparable broken. now its working since two days without going broken.