The Adaptec model 2940UW is High Voltage Differential (HVD) and the (LW) suffix on the Seagate HDD you have connected indicates that this specific drive is Low Voltage Differential (LVD). You should never mix the different technologies. You should be using the 2940 U2W Controller. The flex cable wiring is different between the two. HVD uses single signaling, and LVD uses twisted pair signaling.
i suggest to stay away from HVD devices such as your Adapter, it is to be avoided in most peoples opinions. Not compatible with any other scsi devices(power wise)that are more the main stream and are backwards compatible with most other modern scsi devices. Reason why HVD is outcast is they require a big power supply which makes them undesirable and fatal to all other devices, was an atempt at something different that really was a white elephant in the end.