Galaxian is pretty good in that it has free play built in, so you don't need to keep crediting up the game to play it. Bad thing is that when it's in free play mode, it stays on a static screen waiting for 1 or 2 player button to be pressed.
I've spent a bit of time going through the Galaxian code and have made a little hack that will let the game do its attract screen, but doesn't need coining up to play, just press 1 or 2 player start and the game will begin.
It reads the "unused" DIP switch, if the switch is on, the hack is enabled, if it's off, the hack is disabled and the game runs as normal.
No need for a screenshot as there's nothing to see!
All you need to do is modify 2 ROMs as below (use HxD or similar):-
ROM - galmidw.u
Address 03D7 - change code to C3 00 26
ROM - galmidw.z or 7L (depends on whether you're using Midway or Namco code)
Address 2600 - change code to 3A 12 40 CB 5F 3A 02 40 CA DA 03 3A 11 40 CB 47 3E 01 20 0F 3A 11 40 CB 4F 3E 02 20 06 3A 02 40 C3 DA 03 32 02 40 C3 DA 03 E1 93
