Thanks for the update
I copied the files to a spare disk, reformatted the disk, and then copied the files back to the pool
All is now OK and the larger PSU (15 disks, 650w vs 450w) is making a big difference - less disk startup retries !!!
But be careful, the pin settings of the cables supplied with modular power supplies vary by manufacturer
And you should not just plug the old cables into the new psu