Ribbed Tilt Channel balance

I am having trouble identifying my channel balance. The windows are tilt and look similar to the ribbed channel balances series 750 and 751. When viewing the videos however, this is where the similarities end. I see no easy way of getting to the balances as there are no screws either on the balance or the frame surrounding the window. Furthermore, the numbers imprinted on the hardware do not match the options for the aforementioned series numbers. The information on the hardware is: 28B BSI TO. Any assistance you can provide would be greatly appreciated, both on replacement part to order and replacement procedure.