Multicore checksum mode error solution in J series
It tested in J1/J2/J5/ mini & 100% success
download this file
Put the mobile in download mode (volume down+home key+power).
You can see A menu then press volume up key.
Connect your phone to the PC
Now open ODIN and attach download file to PDA option then click on star.
Wait to finish. When finish mobile reboots and free from multicore checksum mode.
Some set need to flash after this operation then flash your phone with correct firmware.