The problem may be either electrical or mechanical.
If replacing the motherboard did not help, the power supply will need to be tested.
The mechanical parts (clutches, belts, gears, pulleys, etc) will all need to be checked.
Let me know your ZIP code and I can recommend a repairer in your area.
Ok, do you have any experience in repairing these type of chairs, or are you looking for a repairer in your area?
(regarding payments, I am a user of this site just like you, and I have no control over what deposit you choose to pay when you ask your question)