Did you follow Keith's guide & buy the right 'revision' of the board ? If you didn't, that's probably your issue. Go back, read his guide again, and order the right part.
If you did, probably something else on the motherboard causing issues; take it to a local mobile repair shop for diagnosis - I mean, you could always replace the motherboard yourself, but that's going to be not inexpensive (not as expensive as having a Samsung service centre put a new one in, but still...), and they might find the cause of the issue requires a fix that isn't as drastic/expensive as a motherboard replacement.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Probably the best thread ever posted on XDA
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?