i sure your problem solved by this INSTRUCTION but THANKS DONT FORGET.
stage:
1)you must provide orginal gdfs by your phone model(k800.w850...gdfs)it dont necessary CERTAINLY from your your phone just it same by your phone model.
2)conect your phone to box
3)add the orginal gdfs in misc file
4)go to the last tap(setting) and mark SWITCH (format gdfs when writing)
5)come back the frist tap and click on write gdfs
6)when it become complete without you disconnect your phone click on unlock/repair and when it complete disconnect your phone.
I CERTAINLY the phone become REPAIR
HIGH LIGHT:
if the service man say you your phone become repair by flash you CERTAINLY know your phone become damage after a time so just using from this stages.