This is how my Galaga looks inside

It´s one of the three cabs that I got from Paul, the others being Pacman and Ms. Pacman.
I collected it today from my temporary storage (which will be terminated tomorrow

) and I now hope that I will be able to work on it. When I got it from Paul, the game didn´t work, it gave no life sign at all. I now probablý know why, the backdoor ´power safety pin´ (?) was hanging loose and in the ´shutdown the cab´ mode

So it may be working after all, I will try it tomorrow. I already removed the game pcb some time ago and played it since then quite often in one of my candy´s and it is working 100%.
Anyway, I have a few questions:
Where is this little circuit for, mounted on the left panel:

What is this circuit, and is it normal to have such heavy burn marks:

On the transformer board there is one fuse missing, delibaretely done, because the wires are also cut. Where is this fuse for:

There is a fuse on the monitor chassis mounted where I never have seen a fuse before. What is ist for:

In general, is it always a must to have a 115V fuse for Galaga, or can I replace broken fuses with 240V ones, but of course with the right Amperage and Slow blow / Fast blow specs?