Problem
Tilemap layer corruption:
Diagnosis
With Raiden II and similar Seibu PCBs, the first thing I check for are loose legs on the various fine-pitch customs. Despite some mild corrosion on the legs, all were fine.
Probing around the area in the upper left corner where the BG-1/BG-2 mask ROMs area, I noticed weak signals on data lines D4-D7 of SRAM U067:
Piggybacking a known-good RAM onto U067 improved the corruption somewhat:
U067 tested bad out-of-circuit. Replacing it fixed the corruption entirely:
Fix
Replace CXK5863P-35 SRAM at U067
