On 7/1/05, Joe R. <rigdonj at cfl.rr.com> wrote: A couple of minutes with a continuity tester should establish that - OMNIBUS is AA1 to AA1 on all slots, AB1 to AB1 on all slots, etc. No serpentine, no grant lines, no CD slots. It should be clear what to test if you look at an OMNIBUS pinout and compare it to a Qbus serpentine and a Qbus CD pinout. In the case of a 12-slot Qbus CD backplane, don't bother with A and B slots - except for grant pins, they are going to somewhat resemble OMNIBUS - it's the CD pins you should focus on. If AA1 is tied to CA1, that suggests Qbus sinusoidal (if AA1 - slot 1 is tied to AA1 - slot 2, that doesn't tell you much). Repeat until the nature of the backplane is revealed - probably 3-5 scientifically-selected tests should be conclusive. -ethan