One of my older E2000 dental chairs had a peculiar issue: The upper button that serves to raise and lower the chair would not work. The motor would hum but the chair would not move up or down. On occasion the second (middle) button would not work either. The lowest button which moves the chair to a preset would ALWAYS work- and the chair would both raise and recline to the setpoint. This meant the motors were fine. I took the switches and wiring apart and bypassed the switches and still the chair would not raise.
Ebay to the rescue. Had my eye out for a control board for the chair, and when one was available bought it. I installed it quite easily and my chair is now as good as new.
Easy peasy.
Don't be afraid to try to fix your own equipment. Its often quite easy