Recap the logic board for start. All SE/30 logic boards need to be recapped even if the capacitors still look good, believe me they are not.

Also keep in mind that the SE/30 doesn't have a strong PSU so the drives you are connecting may be out of specs for the PSU and drawing too much power.

Termination can also be an issue with newer drives. Make sure all jumpers are set correctly on the HDD.

Try on of your hard drives in another compact mac so you're sure they are not the problem.

If after recapping the SCSI still doesn't work then you're probably gone for hours of testing traces and VIA's.

The cause are often broken VIA's, however I had one case where the SCSI chip was faulty.

Keep us posted