Hi xcell,
You commented about getting someone to attempt repair. Assuming that of the 4 that you have, you want two to work, have you considered simply switching the working electronics and camera/lens. This picture:
Suggests to me that such swaps may be more practical than trying to repair the microscopic electronics. In other words, take the optical section from a dead unit and transplant into the unit that has a dead pixel, etc. If you knew how to solder tiny stuff, that does not look impossible. I think board repair (i.e., getting all four working) would be virtually impossible without specialized equipment and an inordinate amount of time.
In terms of the cost of repair, I suspect a competent person might expect at least $50/hr as a hobbyist to do the swapping. But, I would not be surprised if the cost is $80 to $100 per hour. I am not an engineer nor do I have experience in commercial repairs, but as a rule of thumb for non-hobbyists doing contract work, charges should be about twice what you would expect for salary. At least it was that way in my business.
Finally, I checked Schick/Sirona Dental and at least software support is available for the Schick USB model (current model is the USB4). Maybe there are non-Sirona entities that can attempt the repair.
John