tlscapital wrote:Before you do anything, did you clean the pulley, the platter's side and the belt with some isopropyl ?
No, it's never been cleaned.
Well this little isopropyl clean is always welcome from to time. The belt force in order to work need some grip. Naturally with time, grease/dirt will add up and induce too much "slip". And where all that is needed is horizontal pulling force if too much slide comes in, the whole game will be challenged vertically as well.
But if the height adjustment of the motor pulley and/or platter is either too high or too low,this will set the belt working off it's horizontal axe in regard to the required pull/tractation force/action and the belt will be force to drop either down or up. Surely with the curved tracks on the platter this can be easily adjusted by the eye.