The SCSI2SD v5.0a has a built-in terminator in the form of a resistor pack.
I've tested the voltages of the analogue board and both 12v and 5v are just fine.
It's possible that the problem is actually the SCSI2SD's CD-ROM emulation because I've been copying files from a Floppy Emu and that's...
Well I don't have a PC that takes the same amount of RAM but I can certainly work on the other things. The logic board was recapped, but the analogue board was not.
Thanks for your advice.
I have a recently recapped SE/30, and I have installed a SCSI2SD (v5.0a) inside it. I don't have a (working) CD drive, and the floppy drive is broken, so I configured SCSI device 3 to be a CD-ROM drive, and put the System 7.5.3 installer inside it, along with a copy of the patched "HD SC Setup"...