A fuse under the playfield like that is most likely to be protecting solenoids. Do any of the coil windings look burnt or damaged? Does anything 'kick' in the moment before the fuse blows up?
Early Gottlieb solid-state games used a mixture of control methods for solenoids; many are switched by transistor devices on the driver board, but slingshots retained an electro-mechanical type of switching. The switches closed by the rubber bands complete the coil circuit, with the Game Over relay providing a cut-off when not in play. Thumper bumpers I'm not sure about, though. Later Gottlieb games have a small (credit-card size) circuit board under the playfield for each bumper, but the earliest type doesn't, as I recall. Look at the contacts of the bumper switches - if they're really heavy contact points, and there's another separate switch operated by the bumper linkage, they're similar to the slingshots. If the switching contacts are small, gold-plated ones, the bumpers are transistor controlled.