The power jack had been twisted due to the power lead having had a knock which left the plug emerging from the back panel at an angle less than 90 deg. and very intermittent contact. The power supply is the earlier type (mains tx and bridge) and if the plug on the end of the lead was faulty I would just replace the plug; this was why I wanted instructions for removing the main panel to enable replacement of the power jack.
I have been away for the weekend and haven't had chance to look at it again yet. I will let you know what I find.