Today has been a loooong day for me, but tomorrow I intend to go through the entire +15v rail to test, measure and record each component, across itself and relevant to ground.
There is clearly a not insignificant problem on that rail, so some diligent detective work is on the cards (maybe I should change my user name to 'Colombo'? :)
In the meantime, if anyone has any more suggestions, I am all ears.....
James
James55