One of the most annoying problems I get with galaxian PCB's is when the sprites do not work properly. The entire circuit is a nightmare to trouble shoot and this is complicated because the sprite ram chips are becoming tricky to obtain and are not completely compatible with each other - some seem to need pullup resistors, some do not and on more than one occasion I have had to use different value pullup resistors.
Because of this (and because I had a bit of spare PCB to fill up on an order once) I created a little PCB that would allow you to replace four 27LS00 sprite rams with a single fast 2101. These are easier to obtain and seem to cause much less hassle than the original chips used.
It fits standard Midway and Namco galaxian boards, but I have had a few bootleg boards where the spacing between sprite ram is different so it will not work with those.
As with all of my projects, I (and others) have used it successfully, but I offer no guarantee that it will work for you!
Sprite ram PCB fitted on Namco galaxian PCB
n.b. you don't need to fit all of the pins as you can see above