My Logitech Trackman Marble Wheel's scroll wheel is not working. I assume that the "IR transmitter / Receiver" could be faulty. How to find the correct items?. Any circuit diagrams available.? Other than the scroll wheel, all other functions are OK. Any help in rectifying this problem is highly appreciated.

 

The first step will be to open it by rotating that ring CCW to release the ball. THEN, with it open, remove the ball, and with a clean air source blow out the dust in the area of the scroll wheel. MOST of the time that is the fix. In a worst case, a bit more disassembly may be required, to gain better access to the areas that need cleaning.

 

I did once repair a computer mouse that quit working. It seems that somebody thought it was funny to stretch the cable to the computer and break the wires inside. So the mouse got a shorter tale and functioned again.
Seriously, cleaning out the dust and lint is the first thing to try. THAT has worked for my much newer pointing devices.