Quick question re ProForm 830QT treadmill that stopped working.

Own an older ProForm 830QT. When we went to use it yesterday, the belt would not start. I’ve examined as follows: motor works and turns the belt when 20 volt power supplied to it. Display works fine, and incline works fine. Clearly the signal is not getting from the mother board(s) to the motor. Have checked wire connections, which appear okay. Any advice, other than having to replace either of the boards? I assume there’s some type of relay or switch that supposed to send a signal to the motor. If I have to replace mother board, probably not worth repair costs. There are two "boards," and I'm not sure which is the one to replace, if I did.