I suspect the power supply in the enclosure might be flaky, so I am looking to try a different one.
I have a rack mounting supply, from Vero Electronics, PK60A type 116-10018J. Rated 5V 6A, and +/-12V at 1A.
Needs a chunky DIN connector which I don't think I have. The mating connector will also need wiring terminated with Faston connectors, which I can obtain.
I have a small board I use for powering single STEbus masters from a wall-mounted 5V PSU. It connects the 0V and 5V from a 2.1mm power connector to the 0V and 5V of a female DIN-41612 connector. It has a 5V to +/- 12V DCDC converter, to power the RS232 buffers.
The first converter died due to the excess drain of a chip inserted the wrong way round.
Today I replaced it with a 2W version. https://www.farnell.com/datasheets/2787714.pdf
Small DCDC converters are usually poorly regulated. This one was +/- 18V unloaded. The MC1488 buffer chip is +/- 15V max. Fortunately, the rails drop to about +/-12.5 volts when loaded by this chip.
This worked but did not cure the disk failure problem.