Gee thanks clutchc, I suppose that after 4.5 years I should be grateful. Can you recommend a current replacement ?
With everything disconnected except the CPU it now turns on and off for about 10 seconds at a time. It is definitely caused by the board grounding the power-on pin and then letting it float again, during which time the power ok pin is high and all the voltages are correct.
I can ground the power on pin to keep the psu on, but it doesn't then boot.
I am sure it is a simple fault, the system ran for 9 hours yesterday just fine, after the delayed start.