Thanks to everyone for all your suggestions.
It's working again for now!
I turns out to be a mechanical problem.
I remember form years gone by that some turntables with belt drives need a helping hand to get started by pushing them gently round with a finger on the label if the belt was on it's way out.
This turned out to need quite definite shove with the heel of my hand , but then it started and played OK. There is however a grinding noise from the turntable whenever it is turning that wasn't there before.
I am guessing that something needs lubricating (maybe some bearings needing some love and attention) but the only service documentation I can find is circuit diagrams. Can anyone point me in the right direction towards what may need lubricating please?
Thanks
Simon