I think your encoder may be designed around
this or this
module.
If yours is defective it can be replaced with above..
another link for possible replacement:
https://www.robotshop.com/en/miniatu...e-encoder.html
Alternative is replacement of the whole system with OnStep or similar.
The cost is not prohibitive, it is based on Arduino h/w and steppers are also cheap.. but it involves DIY, so it's not for everyone.