If it is indeed the display you can replace it with another 1602 lcd. They’re pretty cheap on Amazon. If you go back a few pages I also have a 1602 OLED from AliExpress that works.
Also, to clarify further:
The Astro city should have the ground wire with the connector (coming from the connector bracket) attached to the control panel, then the coin chute should have a wire coming from one of the screws (usually the left) which also attaches to the control panel. Then, two...
Pretty much any bolt that holds the control panel in will suffice just fine. You’re just trying to make a path from metal things back to earth so that if it somehow becomes energized you don’t end up being the better path to ground.
I should add my complaint to the pile I guess. He sold me “5380 keys and locks” but no key came and the 5380 locks were actually just the rip-off lookalikes. It was only $20 so I didn’t really care. But ¯\_(ツ)_/¯
It could give us a better idea of peak voltages. I'd put a color bar up through CPS2 or something and see what the peak voltages are on the scope.
With my Mistercade Versus I have to bump the brightness a bit on my MS8 monitor. That should take care of it for you.