Proform treadmill repair. Speed keeps changing, it is not stable. How to solve?

In this video, we can see clearly the motor speed is changing very quickly and it doesn't respond to regulation from console. The problem may be likely in the speed sensor. In fact removing the speed sensor at all, the problem worsen. Another option may be that the treadmill board may be regulated (see blue trimmers). Last (worst option) is that there is a broken motor, controller, or display.

Another video with slightly different conditions

You should check the trimmer first (please note it may be in different position and have different colour as board layout may vary). And speed sensor.

Please also check all connections of the mc2100 board. See additional details pictures below

Connection of Proform controller mc2100

Top view Proform motor housing, it is similar in Weslo, Healthrider, Nordick Track 

Some details of treadmill speed sensor and drive belt vega x pj598

Closer view of treadmill controller connections

If you need these or other replacement parts for Weslo, Nordick track & Proform, check on www.partsfortreadmill.com