How many background checks do you get when u are becoming a pj?

ok so im just curious, i know a guy who got his initial background check before going to meps done,and he is gunna get one when he ships out, and they booked him a job on avionics now he says he is gunna take the past test and if he pes then he is gunna have to have another Background check. is this for real? or is he just pulling my chain