envirogeek has some good suggestions.

Can you boot from floppy and run SCSI Probe with the existing devices attached?

How long is your SCSI cable? Shorter is better.

My instinct is to suspect that SCSI termination power is absent, simply because it is a 68000 compact. Do you have an external hard drive that you can place in the chain which might deliver Term Power? You could even try using a SCSI Zip or Syquest drive.