The 4 amp slow blow is the fuse to the rectifier.
Why would that blow? The downstream 2 amp fuse should have gone first.
Did you drop something / short something out? You may have a bad rectifier, or one that is going bad if you didn't. Look for any arc (dark spots) damage on your PC board, or any "fallen" parts laying on the board.
Fuses don't usually just blow. Something is making this happen. You need to find it, or you'll find your 4 amp slow blow glowing and blowing again.
Watch this fuse after you power the game up. If it starts to glow orange, it's about to blow - turn the game off and start looking for the fault.