Hi, after i redraw a schematic by reverse engineering for the bernina sewing machine ,
I would like to know:
1- The role of the SCR (T80) in regulating the motor speed, which is already controlled by the PWM signal from the T77.

2- Is the R23, R11, and R10 network used to measure back EMF or not?

 

1. I suspect its used as a switch to completely disable the motor so not relying on T77 entirely.

2. R23/R11/R10 sample the voltage across the motor, used as a rudimentary speed feedback. You could think of it as related to back EMF generated as the motor spins.