So if you go they the pinwiki or for us old schoolers clay’s guide, you are half way home as the board has booted. After the initial flicker (meaning the MPU booted) the first flash your not getting is the ROMs booting. I see 2 unmasked roms which have a chance of getting blanked when exposed to any source of uv light. Also the sockets stern used were notoriously bad. I would start there