I have tried with two SCSI drives with the same result. They are not working with this logic board, but when I try with another board from a working SE/30, both SCSI drives are OK and everything is working. Same AB, PSU and cables. So the problem should be in the logic board.
After replacing the the Bourns filter RP10 from another board: same result , no progress.
I measured the voltage on the external floppy drive with the different boards with the same result. Replaced the ROMSIMM from the working logicboard: not better.
Maybee its time to replace the SCSI chip???