The logic board is the DVD drives motherboard, not really a smaller word but maybe that describes it better for ya? By swapping the boards between the drives (must be the same make drive) you are bypassing having to mess with the FW key and such since that's on one of the ICs that are on the board. This will also tell you if the problem is on the board or if it's the laser. If the original drive was broken by you messing with the FW or fried by plugging it in wrong or has some other thing wrong wit it then swapping the logic board isn't going to resolve anything and you'll have to get the key from the original drive. Also, if the problem is the 360 it's not going to matter what ya do to the drives. That new DVD drive should work fine in your 360 and play CDs and DVD movies with no issues, that's a perfect test of that, the only thing it will not play are any game discs because of the key not being the correct one.