What is this ?

This is a small, pre-assembled board meant to be used as a replacement for faulty NEO-257 custom chips on SNK NeoGeo systems like the MV2B...

How to install

Remove the faulty NEO-257 chip with hot air, remove the remaining solder on the PCB pads with solder braid if the surface isn't perfectly flat. Clean up the eventual flux residue with IPA or acetone. Place the NEO-257 replacement board in the right direction (see pin 1 mark), align it precisely, solder the 4 corners using a generous amount of flux, then drag-solder all the sides. The small castellated contacts will "attract" solder by capillary action. Make sure none of the contacts are bridged.

If you decide to install the board with hot air, make sure you don't knock off the board's own chips when the solder will reflow.