I don't think the diode is the issue. I'm gonna assume it was for a controlled lamp in the lamp matrix. GI doesn't have a need for diodes, a string is a simple circuit wired in parallel.
Did you play around underneath with the power on? Something probably broke loose and shorted out your fuse. You may be lucky and the issue resolved with the playfield moved back. Try popping in a new fuse first.
To check a fuse, sometimes you can tell if the filament is toast visually. But sometimes that is hard on the slow blow fuses. You need a multimeter and run a continuity check accross the fuse.
I check for GI shorts by first finding the connectors associated with the blown fuse. I then pull the connectors and check ohms to ground by leaving one lead on a good ground point in the cab, and touching the pins on the connectors with the other lead. Meter should stay infinite ohms or OL, if you get a reading, there's a short on that string.