Missing Chip. This was a converted moon cresta board. The IC at 1.2S (shoehorned in sideways between rows 1 and 2 by the sprite ram) was missing. This was not featured on any schematics I had, so I traced the connections to see what it could be. It basically takes the output from the sprite rams via 1U and passes them on to the usual connections. The purpose of this may not initially be obvious, but it allows you to invert the signals being output from the sprite ram. If you use D2125 ram, then you put a 7404 into this slot to invert the output. If you use 27LS00 sprite ram then you use a 7407 instead.

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