Its really very common for the control belt to fail , I am having these made as the original ones are not very good and fail all the time.
This part of the unit lifts up the heads etc
When you you put a new belt on you need match the pointer up to the through hole in the metal so that its in the right spot, there is not so much info on this, but its straight forward.
But here is the rub, what if the control arm is broken ( common if you put it in the wrong place) how do you know where to put the thing in the first place
So this is for my own information as much as anyone elses
This photo says it all, the control control pot is turned fully clockwise and this is the postion of the arm when thats in that postion, now you can set it how you need.
They are widely used in Teac Tascam kit so this I hope is useful information, later they went to another drive.