Thanks, guys. Yes I think the outer platter will move everything down to its 'correct' position. My current theory is that a worn belt is the culprit so I'm replacing it immediately.
Brilliant, thank you for that. I tried to register for VE but they're not taking new members, alas. Comparing with the arrangement in the diagram, it looks as if the base of my inner platter is not in line with the 45 section of the spindle meaning the belt pulls at an angle and slips off.
I'm unable to find a manual anywhere so I'm not sure how to change the speed from 33 to 45. Looking at the spindle, it appears the belt should be lowered to the bottom section but each time I do this, the belt slips back up to the 33 position on the spindle. Would altering the height of the...