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...
I have been asked this a few times You have to put a spanner to hold where is the thread (there is a shaved off part to Grip) then grab the end with a pair of grips and twist anti clockwise when back to you, its stiff so as often they used loctite to lock it. Dont loose the little magnet there here is some photos to explain
I often get asked about these door and if they can be swapped etc the answer is no The 144 has a bigger door, the 244 246 have a different catch Lad called Tom sent me this photo TASCAM 244 door on top, 246 door on bottom. Note how large 244 hinges are and latch on opposite side. 246 door about 3mm wider.
I had an MSR-24 in to break but my lad managed to break the rear bus in taking them off, but i have just had a customer with same problem, it seems these bushes suffer from the same fatigue as the TSR-8 ones in that they warp a little and its impossible to get them off As a solution you can use the A3440 ones and cut them down at the back they are a perfect fit