First you need to let one zombie alive within earlier round, why? this is game trick to make you focus in finishing the task and you are not disturbed about killing zombies. Begin from bus station in Tranzit. Start with making the turbine by getting the mannequin from map (the central one). then from area under payphone you can get a wing of toy plane. and finally you need a fan sitting by soome seats in window area.
Black Ops 2 Pack A Punch
Then take all of parts above to workbench to contruct the turbine, then go to a bus then drive it to power station (PS). To have better access to power station simply buy your way via the shed door crossway from the bus stop. After you are in PS be quick to activate the power, by collecting circuit board, zombie arm and dont forget for the lever. You can find this 3 parts in small area in small PS. Attach all of those 3 parts to power switch, done with the power.
BO2 pack a punch machine Tranzit
Now place your turbine close to a door , look at lightning bolt symbol, use that symbol to place it. then you have to be the next station with that turbine, if fail you must replace the turbine or ask other game player to help you. Next job is go to the bank, you can use ray gun or grenade to open 2 vault doors. get in the vault and you find another lighting bolt door. (This is almost same with PS door, remember?) .
Black Ops 2 Pack-A-Punch Tranzit
In this step you have to find that this lighning bolt door should be open (if your turbine in PS is still active and you put it in right position). Then go down to the bunker and pick up the battery, stool and of course the shell. Take all that 3 parts to workbench and build a pack a puch machine. This will let you purchase power ups for your weapons. Then you will have special engraving.
Beside this game guide for black ops 2 pack a punch tranzit read other call of duty BO2 game tips tricks here.