Since F4 blew before you replaced the board the problem is downstream as Quench suggests, First thing you need to do is look at the schematic and determine what does F4 do.

Hint.......

Give up? .....

F4 is for the 43v solenoid bus. You probably have a blown coil on the playfield. Unplug the playfield connector from the PS and see if the fuse blows. If not start checking all the playfield coils.

You can narrow it down by unplugging the other connectors but generally speaking if f4 blows right away on power up it's probably a shorted bridge.