You have done all the obvious things.
You have done the obvious things. This is a servo controlled turntable. I do not know this turntable, but I suspect it has a DC servo motor. A servo system is a feedback system. In a DC servo system the motor is driven by a DC amplifier. There are sensors in the motor, that send signals back to the amp control circuit, to keep the speed precisely regulated. Your fault could be with the motor or the control board.
In an AC motor system there is usually a square wave generator driving the motor, and the motor usually has some type of Hall Effect sensing tack that sends pulses back to the control circuit to keep everything regulated.
Both of these circuits I find put you on stretch to analyze. At least they do me, but I'm just a physician so what do I know. You need a good scope and frequency counter as well an good amplified meter at the minimum. Of course you need the circuit and service manual.
I tried to see if I could get a service manual for free on line, but I couldn't. There is a chap on eBay in Australia that has a service manual in pdf, that he will Email for $7.50.
http://cgi.ebay.com/Sansui-Rotel-Pioneer-Sony-Marantz-owner-service-manual_W0QQitemZ200174625450QQihZ010QQcategoryZ295QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
If it is the motor that is the problem, then you will likely be out of luck, if Rotel do not have one. If it is the board that is at fault it is almost certainly serviceable, unless there is an integrated circuit at fault, that is NLA. Usually however when a chip fails the motor does not run. I have found these faults are usually due to aging capacitors getting out of speck, and less often a motor problem.
If you really like this turntable you might want to pick up another on eBay as a parts machine. You might find a seller who has a motor and or control board for sale. If you can find one, I would swap out the board first.
I hope this helps.
