This method works for any 6.1 and 6.5, and even radio rom.
*** Some Kingston brand may have problem to use SD method, no solution other than use RUU method ***
0. Make sure x1 is hard-spl first
1. Make sure yr micro-sd is formatted w/ fat-32
2. rename the image file (normally "ruu_signed.nbh") to Kovsimg.nbh, copy that to the micro-sd, and put that it yr X1
3. Make sure X1 is disconnect to your PC to avoid goes to serial mode (AC power source is OK)
4. Bring x1 to boot-loader mode by turning off the x1 completely. Hold the "volume down" button on the right, and hold the power on button until you see the tri-color screen.
5. Then follow the on-screen instruction