If you removed your chip you won`t be able to play backups,just originals unless you are using swapmagic disc set to load backups,most likely spot for a bridge to happen is the bios chip which is a fairly large ic with fine legs on it,and all chips have wires soldered to the bios chip [
excluding dms4 lite and pro E.Z.I series chips which are solderless ] and this is were bridges happen it just take a very little solder to make a bridge,it would be a good idea to take a magnafying glass to make sure of no bridges around the bios chip,and also check the other area`s that you unsoldered to make sure no solder is crossing any components.Also make sure that all connectors and ribbon cables are plugged in securely also,but if to much heat is given to components they can burn out.The newer slimline PSTwo`s seem to have a better laser`s than that first batch of slimline consoles.Hope info helps.