[Mondial]

That turntable uses a rubber idler wheel to transfer motion from the motor shaft to the turntable platter. The wheel with the rubber "tire" at the rim is the idler. Check and see if the rubber surface is not hardened and glazed, which would make it slip. Also check if the motor shaft turns freely. This is the small shaft under the idler in the photo. Sometimes the oil in the motor bearings gums up and prevents it from turning.