The following shows the location of the 42pin custom IC I/O controller
"51" and the steps to replace this chip
on a Galaga or Bosconian boardset.
Note: correct orientation of the chip is essential for it to operate !
Layout of the Galaga and Bosconian CPU board are identical
Install as shown ! Correct orientation is critical !
Pin 1 is marked on th 51 replacement
Final location in place on board