IIRC, on Defender there is a secondary test menu that you need to enter. I can't recall right now how to get into that menu, but my recollection is that a two-blink on all 4 LEDs was a pass and that notihg remaining lit was a ROM error.
Williams had decent test menus -- I would try those first (I don't have a manual handy, but you can find them from the Restoration links in the wiki).
Cheers