najua kuwa s6 haina kava linalofunguks bt always imei huwa written at the back.. imei kuanza na 99 cyo tatizo kwani ziko hata zinazoanza na 01, 86 na cyo lazima zianze na 35... kama hakuna imei at the back then u must change to new one and not repair.. hata ukitaka kuwrite cert still hakuna free cert for such models na hata ukibahatisha kuipata bac haitochukua muda mrefu kabla haijawa blacklisted again so ur better option ni kununua cert which costs arround 30$ na kuwrite hyo cert u need professional tools