I've done further checking.
The machine is rated for use in the UK at 230V,and the main selector voltage switch is set correctly and the two fuses are rated correctly (2.5A and 0.5A).
I checked the +20V, -10V and -40V regulated outputs using a triggered scope and they seem to all ok although some to not reach final voltage before the PSU cuts off.
I have checked the *inputs* to the three regulators and found the following:
TP4 +20V? Input spec = 23V +/- 2.3V? ?Actual = +21.66V (in spec)
TP5 -10V Input spec = -13V +/- 1.3V? Actual = -12.2V (in spec)
TP6 -40V Input spec = -45V +/- 4.5V Actual = -55.2V @220V and -56.3V @ 230V (not in spec)
So it seem likely that VR2 (57.5V zener) is tripping the over voltage circuit.
I can't see why one rail would be out of spec if the others are ok. There is not much between that and the rectifiers from the main inverter. I have checked the smoothing cap C11 and replaced it (although it tested fine). If R11 has drifted higher than 110k, could that make so much difference?
thanks for all suggestions - the help on this group is great.
Tony
