Some pins, and pads, look too dry on that old resoldering job, didn't get "wet" with a good flow of solder. I'd re-work the solder side on that board. It may not fix the immediate problem(s), but it needs to be done right, so you can move on with your troubleshooting.

Only noticed 8 fuses when I took a quick look in the manual (section XI. Parts List). 1A slo Playfield. 3/16A Sol. Driver/Voltage Reg., Rectifier 3/4A slo & 4A & 5A & 20A & 3A slo. And I only have seven fuses that I can find in my cabinet, which has the Stern SDU-100 solenoid driver board (no fuse!).

You have good taste. SI was my first solid state pinball.

First take, wow, also thinking too much color for my tastes. But I like the alien on the backglass, the way it really pops out. Imagine if the arcade had it looking like that back in the day.

Weird. Looks as if the glass wasn't fully printed, or somebody cleaned it with the wrong stuff and had to repair it. Should be a silvery masking layer everywhere except where you want light coming through, and that includes closely outlining the lettering around "Bally" and "Space Invaders". Here the masking is done roughly and it is missing in many places. Blue lettering would have been created in the small rectangular windows with that masking layer.

double post