Tino Insana says:
A few minor things and one major.
Needs a new timing belt, disc tray, mat etc... but the tray won't spin for some reason, although I think the motor is fine. Tried the belt in all kinds of positions and had a play with the central 'cogs', but can't seem to get it going. Every other major thing seems fine, just that.
How's the 'disc tray' mounted? By disc tray I assume you mean the sub platter that the main platter rests on. You mention the 'timing belt' so i'm guessing it's belt drive rather than direct but i'm not sure what the 'cogs' you mention would be (except maybe for the tone-arm return if it has that feature). In the vast majority of belt drives the sub platter connects directly to the motor via the belt. Is this the case? If so then if the sub platter wont turn then it's possible there's corrosion where the bearing contacts the spindle. Or just a lack of proper oiling if it's been unused for some time. Can you turn the sub platter by hand?
It's all speculation without knowing the exact model or having a look myself though. I don't think there's many places thet offer services on old marantz t/tables anymore. Even current Marantz dealers don't have the knowledge or parts available i'm afraid.