Kudos to the RaidSonic customer service team over in Germany. Replied within a couple of hours to my "is it possible to get replacement system boards for my icy box enclosure" email.
Unfortunately for me, the answer, after providing the serial number, was "that’s from first generation and old. We can’t replace this PCB".
Fortunately for me, I have replacement capacitors, and voltage regulator IC in the post, so fingers crossed I can coax it back to life.