From what I see: You have a 20 amp fuse blowing, and that is a lot of current. Most likely a direct short somewhere - a bad socket, a socket shorted against something else or something like that. No sound is likely a separate problem, as sound is generated in the backbox, a separate circuit from the GI. Solve one problem at a time and you should be fine.

Sound needs the G.I. ac functioning to work. I just had a call where the 20 amp fuse holder metal was very much discolored and needed to be replaced.

Not saying this is the OPs issue at hand.

Ahh, didn't know that. Grabs gen illumination bus to make -5V rail. That changes things a bit, since the problem could be there. I'd probably disconnect that connector that feeds in, troubleshoot the GI (if still failing) then examine these few entry components before reconnecting.

Did you pinch the ground strap in the head against one of the GI wires for the back glass? That's a nice dead short.

You accidentally shorted the GI when you put the game together. Make sure none of the GI braid wires are accidently sorted to the Switched Illumination bus wire or ground shorted.

Have you checked the GI VAC from the transformer? It may have shorted internally?

Remove all plugs except for the main transformer to the power supply board and see if it blows?

I must start with referring to the GI having a Bridge Rectifier related to it, my apologies, I was wrong and thinking of the Switched Illumination.

I have just had exactly the same thing in a Bally Vector, the green slime on one pin.

I believe it to be the 'breakdown' of the cable insulation itself.

I used a cotton bud with methylated spirits, an alcohol.

If you are unable to remove the pin that is.

And also a small stiff haired paint brush or baby screwdriver with a rag on it to get in and around the pin.

But, that won't be causing the fuse to blow, but still should be cleaned up IMO.

Also just my opinion, but I see the four 100ohm in parallel resistors to give you your 25ohms, I'd be swapping it out and the 600ohm and raising them off the board, but this isn't necessary for your game to work.

As your GI has proved good, I'd be plugging the connectors onto the power supply board one at a time to see what part of pinball is causing your 20A GI fuse to blow.

A pic of the reconditioned power supply
VPS (resized).JPG

well done, great to hear it's all sorted