Thank you for your replies.

I disconnected the output from the PSU when measuring the voltages as I didn't want it to cause any further problems while I was testing.

I did a bit more investigating. I took off its case, discharged its main cap with a large resistor just in case it still had 400v.

Now I can see its a XP POWER ECM40UT31 so ordered one from Farnell. I see it has a small pot next to the outputs. I don't know if Meridian adjust it in any way.

G61RSL, 598, DSP5200SL, DSP5200HC, DSW