I've got a box full of various models of AHA2940
and 3940 that don't work
in all
systems, and most of them don't work in any system at all. Most of them
exhibit
one of two symptoms. (1) they don't work in systems with a bus clock >25 MHz,
or (2) they don't find any SCSI devices, irrespective of the fact that other
2940's, among others, find them just fine. The longest I've ever had a 2940AU
(the only type that seems to work in all applications) last is 6 months.
Fortunately, the old 152x types and 151x types seem to keep on going ...
Adaptec has a 5 year warranty on the 2940 cards, just RMA them.