On Thu, 25 Feb 2016 12:53:04 -0000 (UTC), Cursitor Doom
wrote:

snip
I didn't get the chance to find out! Began this morning trying to get
some voltage readings off the psu outputs and there was nothing there to
read. To cut a long story short, further investigation reveals something
has gone short-circuit on one of the signal boards. When the psu is
removed and run from my make-shift dummy load, it's still 'fine' with its
new diode (not quite right, but functioning to high degree). So clearly I
jumped the gun slotting it back in the scope when it still wasn't 100%
and now it's damaged something - typical!

Sounds more like you're getting closer to root cause.

Troubleshoot the (unidentified?) signal board.

RL